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Cold start issues 1981 Briggs 11hp model 25

#1

3

350Rocket

https://photos.app.goo.gl/nzQs7vEqYxtctRd9A
Cold start issues first start of the day. Runs perfectly after that. Thought the choke was too lean so tried bending the choke rod to shorten it.. didn't help. Not sure why it's smoking so much while cranking when it never smokes while running normally. I'm an old car guy but not a small engine expert. The first video was after 3-4 attempts to start and I realized I should record it. It started this several weeks ago seemed to coincide with temperature drop which made me think it was choke adjustment. Before it would start first try every time.
History is it sat for 3 years after a mouse chewed the ignition coil and the previous owner gave it to me. Upgraded to electronic ignition and cleaned mouse nest from fan blades, ran almost perfect. Has leaked gas out of carb for many years which probably saved the carb before it sat. I started shutting the valve when parked. Maybe it's still flooding internally after parking for the night?
Any ideas are appreciated.


#2

A

artemjemmy

On your first video when it finally starts running do you have it at full throttle? Seeing it take a long time to rev up without any load immediately indicates to me low compression. I have seen it many times on tecumseh 5hp snowblower engines, never on a briggs. Also, that is not smoke, that is atomized gasoline vapor from the carb. That combined with the low compression symptoms makes me think you have a leaking intake valve seat or you need to adjust the intake valve lash, which on those flatheads is only possible by grinding the valve down.


#3

3

350Rocket

artemjemmy said:
On your first video when it finally starts running do you have it at full throttle? Seeing it take a long time to rev up without any load immediately indicates to me low compression. I have seen it many times on tecumseh 5hp snowblower engines, never on a briggs. Also, that is not smoke, that is atomized gasoline vapor from the carb. That combined with the low compression symptoms makes me think you have a leaking intake valve seat or you need to adjust the intake valve lash, which on those flatheads is only possible by grinding the valve down.
Click to expand...
Hopefully Thursday night with my friends help I will know more. I took off the float bowl and sprayed the needle and seat, reinstalled and now I can't get it to stay running without external fuel. Unfortunately there was a few things at play here and I don't know what caused it. It was running great Besides leaking oil like a sieve. Several years old spark plug looked like new. I think the engine is good besides the oil leaks.

I installed a fuel filter in line with the carb after noticing a ton of dirt in the tank...this was after cold start issues began but before it failed to stay running at all...messed around with my new line and fuel filter and adjustment of the screw in the bottom of the float bowl...none of that seemed to be the issue.

Will look at it further Thursday night but I suspect it's either something I did, or dirt in the carb that I moved to a worse spot when trying to fix the original cold start issue.

I've never seen oil smoke from the exhaust even under heavy load or start up. And it runs crazy smooth for an ancient single cylinder so it's hard to believe any major engine issues.


#4

A

artemjemmy

350Rocket said:
Hopefully Thursday night with my friends help I will know more. I took off the float bowl and sprayed the needle and seat, reinstalled and now I can't get it to stay running without external fuel. Unfortunately there was a few things at play here and I don't know what caused it. It was running great Besides leaking oil like a sieve. Several years old spark plug looked like new. I think the engine is good besides the oil leaks.

I installed a fuel filter in line with the carb after noticing a ton of dirt in the tank...this was after cold start issues began but before it failed to stay running at all...messed around with my new line and fuel filter and adjustment of the screw in the bottom of the float bowl...none of that seemed to be the issue.

Will look at it further Thursday night but I suspect it's either something I did, or dirt in the carb that I moved to a worse spot when trying to fix the original cold start issue.

I've never seen oil smoke from the exhaust even under heavy load or start up. And it runs crazy smooth for an ancient single cylinder so it's hard to believe any major engine issues.
Click to expand...
All you have to do to confirm or deny carb problems is shut off the fuel and drain the float bowl to ensure the carb can't contribute in any way, then spray starting fluid, carb cleaner, or brake cleaner into the intake and see how well it starts. If it still has trouble starting and revs up sluggishly like I saw in your video, then the carb is almost definitely not a problem. That fuel mist puffing back out the intake so much is definitely a concern to me.


#5

3

350Rocket

artemjemmy said:
All you have to do to confirm or deny carb problems is shut off the fuel and drain the float bowl to ensure the carb can't contribute in any way, then spray starting fluid, carb cleaner, or brake cleaner into the intake and see how well it starts. If it still has trouble starting and revs up sluggishly like I saw in your video, then the carb is almost definitely not a problem. That fuel mist puffing back out the intake so much is definitely a concern to me.
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The last time I messed with it after confirming my fuel filter and new fuel line wasn't the issue...it stayed running on external fuel....despite fuel being present at the clear fuel filter.... at this point choke adjustment needs to be redone since I bent the rod trying to get it to close similar to what I would want on my 38 years old Oldsmobile....

However there were times prior that I got black smoke out the exhaust like it was too rich. Combine that with too many changes since the problem started and before it got worse... it's hard to say.


#6

3

350Rocket

artemjemmy said:
All you have to do to confirm or deny carb problems is shut off the fuel and drain the float bowl to ensure the carb can't contribute in any way, then spray starting fluid, carb cleaner, or brake cleaner into the intake and see how well it starts. If it still has trouble starting and revs up sluggishly like I saw in your video, then the carb is almost definitely not a problem. That fuel mist puffing back out the intake so much is definitely a concern to me.
Click to expand...
I will have my friend bring his compression tester when he comes....if it is a valve issue think it could just be carbon buildup? Not really a huge deal to clean it all up and fix the oil leaks over the winter if the rest of the engine is a good as o think it is...


#7

A

artemjemmy

350Rocket said:
I will have my friend bring his compression tester when he comes....if it is a valve issue think it could just be carbon buildup? Not really a huge deal to clean it all up and fix the oil leaks over the winter if the rest of the engine is a good as o think it is...
Click to expand...
When tecumseh flat head engines get the low compression problem it is because the valve lash (gap between stem of valve and tappet) is either way too small or they are literally touching (measured at TDC compression), so the valve (either intake or exhaust, in your case it seems like intake) will stay open and blow out compression gas. I have theorized that this valve lash changes because the valve seat actually sinks lower into the block over time, causing valve lash to get smaller, but I can't prove it really.


#8

A

artemjemmy

350Rocket said:
I will have my friend bring his compression tester when he comes....if it is a valve issue think it could just be carbon buildup? Not really a huge deal to clean it all up and fix the oil leaks over the winter if the rest of the engine is a good as o think it is...
Click to expand...
I have no idea what compression would be considered "acceptable" on those big briggs flatheads, but I would personally use a leakdown tester, not a compression tester on small engines. Any good engine with minimal leakage should really have at least 2/3 of the pressure on the secondary gauge as compared to the first gauge when measuring leakage. If it is really leaky you should be able to hear air leaks out the exhaust/intake/crankcase


#9

3

350Rocket

artemjemmy said:
When tecumseh flat head engines get the low compression problem it is because the valve lash (gap between stem of valve and tappet) is either way too small or they are literally touching (measured at TDC compression), so the valve (either intake or exhaust, in your case it seems like intake) will stay open and blow out compression gas. I have theorized that this valve lash changes because the valve seat actually sinks lower into the block over time, causing valve lash to get smaller, but I can't prove it really.
Click to expand...
One more day until I find out for sure... But if it's a valve issue it has to be due to buildup causing it to stick and not wear from a sinking valve seat... because it started as a cold start issue...then wouldn't run at all, then ran like new again for several minutes before dying again and refusing to start. I can see a sticking valve but not a worn part.


#10

A

artemjemmy

Also, does the engine idle, or does it die out immediately when you move the throttle to "slow"? If it does die, is it very difficult to restart? Can you see roughly what the position of the throttle plate is off of the carb idle stop screw when you have it running at full throttle no load? If the throttle plate is quite far off of the idle stop screw, that would be a problem. These are all checks and symptoms of low compression.


#11

3

350Rocket

Well she seems to be fixed. I assumed you were probably right about a valve issue... unfortunately I don't have a before compression test result. Last night I pulled the plug and sprayed a bunch of cleaner on and in behind the valves the best I could, spun it over a few times and sprayed more cleaner...let it sit until tonight. We sprayed one last dose of combustion chamber cleaner in and then some oil and trans fluid mix, then spun it enough to get rid of the excess... did a compression test...about 151psi...I didn't think these engines even made that much compression? Put the new plug in and with a ton of smoke it reluctantly fired up and stayed running.....let it clear out and adjusted the main jet screw until it ran the smoothest and mowed some grass with it. So far it's running perfectly. I'll see how it is on a cold start since that's where the issue originally started. Thanks for the advice.

Attachments





#12

A

artemjemmy

350Rocket said:
Well she seems to be fixed. I assumed you were probably right about a valve issue... unfortunately I don't have a before compression test result. Last night I pulled the plug and sprayed a bunch of cleaner on and in behind the valves the best I could, spun it over a few times and sprayed more cleaner...let it sit until tonight. We sprayed one last dose of combustion chamber cleaner in and then some oil and trans fluid mix, then spun it enough to get rid of the excess... did a compression test...about 151psi...I didn't think these engines even made that much compression? Put the new plug in and with a ton of smoke it reluctantly fired up and stayed running.....let it clear out and adjusted the main jet screw until it ran the smoothest and mowed some grass with it. So far it's running perfectly. I'll see how it is on a cold start since that's where the issue originally started. Thanks for the advice.
Click to expand...
Now that I look closer at the second video, it is very possible that the engine is just flooding out overnight from a slowly leaking carb. Does it make quite a bit of white smoke on cold starts? A spark plug fouled with gas will make the same symptoms as that slow running and dying in the first video. Now that I look at the second video, the engine revs up way too quickly from a low speed for it to have low compression, and it also seems to idle well too.


#13

3

350Rocket

artemjemmy said:
Now that I look closer at the second video, it is very possible that the engine is just flooding out overnight from a slowly leaking carb. Does it make quite a bit of white smoke on cold starts? A spark plug fouled with gas will make the same symptoms as that slow running and dying in the first video. Now that I look at the second video, the engine revs up way too quickly from a low speed for it to have low compression, and it also seems to idle well too.
Click to expand...
Normally no smoke out of the exhaust even on cold starts where it was having trouble starting. I think I read that this model of 1 piece Flojet carb only leaks externally when the needle and seat is sticking..which is consistent with the puddle it leaves on my garage floor if I don't shut the fuel off when I park it.


#14

A

artemjemmy

350Rocket said:
Normally no smoke out of the exhaust even on cold starts where it was having trouble starting. I think I read that this model of 1 piece Flojet carb only leaks externally when the needle and seat is sticking..which is consistent with the puddle it leaves on my garage floor if I don't shut the fuel off when I park it.
Click to expand...
This still has the potential to flood the engine on cold starts because if gas can leak out of the carb from the float bowl gasket or the bowl vent, it definitely has the potential to leak gas into the intake manifold, which can still cause starting issues. I am doubting that you had an inherent compression issue now, with a reading like you showed.


#15

3

350Rocket

artemjemmy said:
This still has the potential to flood the engine on cold starts because if gas can leak out of the carb from the float bowl gasket or the bowl vent, it definitely has the potential to leak gas into the intake manifold, which can still cause starting issues. I am doubting that you had an inherent compression issue now, with a reading like you showed.
Click to expand...
This must be the problem. It's back up to 61 degrees Fahrenheit after being almost down to freezing this morning...just started it up and it's doing what the problem started as....several cranks to get it to start. Could see a slight bit of black smoke a few times. After the first couple start/stall with choke on I took choke off and it would still start/stall and each time run slightly longer...up to several seconds until it finally stays running and runs nice and smooth. Cranking the throttle up when it's still cold makes it bog and near stall but after about 5 minutes idling it revs nice and quick. I'm guessing the carb is flooding like you say and there never was a compression issue. The plug may have been too fouled which caused it to completely fail to stay running and the new plug fixed that.


#16

3

350Rocket

artemjemmy said:
This still has the potential to flood the engine on cold starts because if gas can leak out of the carb from the float bowl gasket or the bowl vent, it definitely has the potential to leak gas into the intake manifold, which can still cause starting issues. I am doubting that you had an inherent compression issue now, with a reading like you showed.
Click to expand...
I'm still having a hard time understanding where it's getting into the engine... float bowl gasket will leak onto the ground.... I'll have to look at it closer to see the bowl vent but since my first attempt to clean the float/needle and seat didn't work I may just take it to a guy I used to work with who retired from the ford dealership and works on small engines now. It's not worth fixing myself this season since we have one or 2 more mows before frost and snow take over and it will be parked until late spring.


#17

R

Richard Milhous

150 psi??? I've had cars that blew 120 or less and ran fine, minus a little oil. I had a Briggs 3.5 that was blowing 35 psi when I retired it because the deck was rusted out.


#18

A

artemjemmy

350Rocket said:
I'm still having a hard time understanding where it's getting into the engine... float bowl gasket will leak onto the ground.... I'll have to look at it closer to see the bowl vent but since my first attempt to clean the float/needle and seat didn't work I may just take it to a guy I used to work with who retired from the ford dealership and works on small engines now. It's not worth fixing myself this season since we have one or 2 more mows before frost and snow take over and it will be parked until late spring.
Click to expand...
Put an inline fuel shut off on the fuel line to the carb. When you are done mowing, shut the valve off. The next time you use it, turn the valve back on and try starting it. If it starts fine, carb leaking is definitely what was causing the starting issue.


#19

B

bertsmobile1

350Rocket said:
I'm still having a hard time understanding where it's getting into the engine... float bowl gasket will leak onto the ground.... I'll have to look at it closer to see the bowl vent but since my first attempt to clean the float/needle and seat didn't work I may just take it to a guy I used to work with who retired from the ford dealership and works on small engines now. It's not worth fixing myself this season since we have one or 2 more mows before frost and snow take over and it will be parked until late spring.
Click to expand...
EPA has mandated that no fuel shall be leaked to the outside world
Thus the bowl vent is on the engine side of the carb, usually in the flange
So the fuel that you would see & smell leaking and fix right away completely drains the tank into the sump
You pull the starter, & hydro lock the piston breaking the rings, bending the rod or blowing the gasket
So now you have 3 quarts of fuel contaminated oil in the engine add another 4 cups for 2 oil changes to remove the fuel all waste.
SO the fuel comtaminated oil sits in a pan & the fuel evaporates into the atmosphere
Never really understood what it was supposed to achieve apart from wasting a lot of fuel , oil & mower parts .


#20

3

350Rocket

artemjemmy said:
Put an inline fuel shut off on the fuel line to the carb. When you are done mowing, shut the valve off. The next time you use it, turn the valve back on and try starting it. If it starts fine, carb leaking is definitely what was causing the starting issue.
Click to expand...
I mentioned above that it has this from the factory, I've been shutting it off which is why I don't know how it could flood the carb.


#21

3

350Rocket

bertsmobile1 said:
EPA has mandated that no fuel shall be leaked to the outside world
Thus the bowl vent is on the engine side of the carb, usually in the flange
So the fuel that you would see & smell leaking and fix right away completely drains the tank into the sump
You pull the starter, & hydro lock the piston breaking the rings, bending the rod or blowing the gasket
So now you have 3 quarts of fuel contaminated oil in the engine add another 4 cups for 2 oil changes to remove the fuel all waste.
SO the fuel comtaminated oil sits in a pan & the fuel evaporates into the atmosphere
Never really understood what it was supposed to achieve apart from wasting a lot of fuel , oil & mower parts .
Click to expand...
Did they make this change before 1981? The previous owner had a gravel floor in his shed and the gas would be completely empty when I came back several weeks later to mow his lawn..oil always looked perfect (but it was always being topped up as it leaks like a sieve). No smell of gas. In my concrete garage or wooden shed if I notice I forgot to shut the valve, 24 hours later I'd have a large pool of gas under it.
I guess whatever is left in the bowl would be enough to flood it slightly so I should shut the valve and let it run out? I guess with gravity feed in the morning it should fill up quickly enough for fuel to be present for a quick startup to confirm it was flooding?


#22

3

350Rocket

Richard Milhous said:
150 psi??? I've had cars that blew 120 or less and ran fine, minus a little oil. I had a Briggs 3.5 that was blowing 35 psi when I retired it because the deck was rusted out.
Click to expand...
I've searched online for typical compression results and it's tough since most of the newer engines have ACR which lowers cranking compression. I don't know if the model 25 Briggs has it (it does not say "easy spin" on it like our old 74 8hp did). Either way I haven't seen anyone with 150 psi on a small engine like this.


#23

3

350Rocket

bertsmobile1 said:
EPA has mandated that no fuel shall be leaked to the outside world
Thus the bowl vent is on the engine side of the carb, usually in the flange
So the fuel that you would see & smell leaking and fix right away completely drains the tank into the sump
You pull the starter, & hydro lock the piston breaking the rings, bending the rod or blowing the gasket
So now you have 3 quarts of fuel contaminated oil in the engine add another 4 cups for 2 oil changes to remove the fuel all waste.
SO the fuel comtaminated oil sits in a pan & the fuel evaporates into the atmosphere
Never really understood what it was supposed to achieve apart from wasting a lot of fuel , oil & mower parts .
Click to expand...
So I just did another cold start...took about 15 tries to keep it running again. Then I shut off the fuel again and let it run out and die for tomorrows cold start.
Then I pulled the plug cause I figured maybe it's fouling the plug slightly with whatever way left in the bowl. I'll attach a picture of the plug. It looks pretty dry to me at the electrode. A bit of black around the edge but it still had cleaner/oil in the combustion chamber when started and smoked like uncle bucks car for the first several minutes. Only has about an hour run time on the plug.

Attachments









#24

R

Richard Milhous

bertsmobile1 said:
EPA has mandated that no fuel shall be leaked to the outside world
Thus the bowl vent is on the engine side of the carb, usually in the flange
So the fuel that you would see & smell leaking and fix right away completely drains the tank into the sump
You pull the starter, & hydro lock the piston breaking the rings, bending the rod or blowing the gasket
So now you have 3 quarts of fuel contaminated oil in the engine add another 4 cups for 2 oil changes to remove the fuel all waste.
SO the fuel comtaminated oil sits in a pan & the fuel evaporates into the atmosphere
Never really understood what it was supposed to achieve apart from wasting a lot of fuel , oil & mower parts .
Click to expand...

Like those stupid gas can spouts that make it difficult or impossible to refuel. Sooner or later they cause a massive fuel spill, but we're spared the tiny amount of vapor that would have escaped from normal spouts!


#25

3

350Rocket

Richard Milhous said:
Like those stupid gas can spouts that make it difficult or impossible to refuel. Sooner or later they cause a massive fuel spill, but we're spared the tiny amount of vapor that would have escaped from normal spouts!
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I'm not a big EPA fan, my daily driver 3 of the 4 seasons is an 84 Oldsmobile with a 350 V8 from a 75-76 Cutlass. My work truck and winter beater is a 2005 Silverado. The less technology the less things to mess up imo.


#26

R

Richard Milhous

350Rocket said:
I'm not a big EPA fan, my daily driver 3 of the 4 seasons is an 84 Oldsmobile with a 350 V8 from a 75-76 Cutlass. My work truck and winter beater is a 2005 Silverado. The less technology the less things to mess up imo.
Click to expand...

Once upon a time there was a need for the EPA. Garbage, raw sewage, and all sorts of industrial waste were dumped into rivers. Coal power plants spewed millions of tons of fly ash and sulfuric acid. Cars added huge amounts of carbon monoxide, nitric oxide, and hydrocarbons.

Now that things have been cleaned up, we have the same problem with EPA as we do with a thousand other agencies and programs: They are immortal. It's almost impossible to cut the funding of a government program, let alone shut it down. EPA has to do *something* to stay funded, so they chase after any fantasized problem, like a germophobe that scrubs their hands until they rake the skin off.


#27

B

bertsmobile1

Yes & No Richard .
It is needed now more than ever to clean up the environmnt
However it has to front up against companies like Monsanto & McDonalds with a bigger petty cash account than the EPA's entire operational budget.
Thus they concentrate on the easy targets like lawn mowers & chain saws rather than agrcultural chemicals , avaition & marine .
Congress takes numbers as proof so 1,000,000 meaningless prosecutions carrys more weight than a single industral one that actually makes a difference.


#28

3

350Rocket

So, after running thrcfurk
bertsmobile1 said:
Yes & No Richard .
It is needed now more than ever to clean up the environmnt
However it has to front up against companies like Monsanto & McDonalds with a bigger petty cash account than the EPA's entire operational budget.
Thus they concentrate on the easy targets like lawn mowers & chain saws rather than agrcultural chemicals , avaition & marine .
Congress takes numbers as proof so 1,000,000 meaningless prosecutions carrys more weight than a single industral one that actually makes a difference.
Click to expand...
Yes. They could do a lot of good but they just waste money.


#29

R

Richard Milhous

bertsmobile1 said:
Yes & No Richard .
It is needed now more than ever to clean up the environmnt
However it has to front up against companies like Monsanto & McDonalds with a bigger petty cash account than the EPA's entire operational budget.
Thus they concentrate on the easy targets like lawn mowers & chain saws rather than agrcultural chemicals , avaition & marine .
Congress takes numbers as proof so 1,000,000 meaningless prosecutions carrys more weight than a single industral one that actually makes a difference.
Click to expand...

I know all too well, I've worked for government 15 years. But there's no denying things are a lot damn cleaner than they were sixty years ago. Even though they still let ships burn bunker oil.

Congress don't know numbers from a hole in their *ss unless those are written on a check.


#30

B

bertsmobile1

Richard Milhous said:
I know all too well, I've worked for government 15 years. But there's no denying things are a lot damn cleaner than they were sixty years ago. Even though they still let ships burn bunker oil.

Congress don't know numbers from a hole in their *ss unless those are written on a check.
Click to expand...
And consider jet air travel to be essential regardless of the volume of unburned fuel that pours out the exhaust during take off
One jet would put more Jet 1 into the atmosphere on a single heavy take off than every 2 stroke in the country .
And then there is water , both in lakes & streams as well as artesian water polluted by fracking etc etc etc


#31

3

350Rocket

bertsmobile1 said:
And consider jet air travel to be essential regardless of the volume of unburned fuel that pours out the exhaust during take off
One jet would put more Jet 1 into the atmosphere on a single heavy take off than every 2 stroke in the country .
And then there is water , both in lakes & streams as well as artesian water polluted by fracking etc etc etc
Click to expand...
Most things come down to money. Yes it makes sense to create more efficient/lower emissions equipment as time goes on. Fixing the old gear and not having to scrap it and manufacture the replacement machine is probably a lot better for the environment even if the old machine creates more emissions. But that doesn't help the economy at all does it?


#32

3

350Rocket

350Rocket said:
So I just did another cold start...took about 15 tries to keep it running again. Then I shut off the fuel again and let it run out and die for tomorrows cold start.
Then I pulled the plug cause I figured maybe it's fouling the plug slightly with whatever way left in the bowl. I'll attach a picture of the plug. It looks pretty dry to me at the electrode. A bit of black around the edge but it still had cleaner/oil in the combustion chamber when started and smoked like uncle bucks car for the first several minutes. Only has about an hour run time on the plug.
Click to expand...
Yesterday I shut off the fuel and let it completely run out (took like 60 seconds at least idling before it finally died - maybe the shutoff isn't sealing perfectly?) This morning I turned on the fuel and immediately tried to start it ..still the same thing, fires briefly and stalls...over and over again firing a little bit longer each time before dying. No real noticeable smoke or smell despite being in my garage. I ordered a new Chinese carb from the states so I guess that's my next attempt to fix it. I've been driving carbureted cars for 22 years since I was 16 and this behaviour seems odd to me, but obviously a single cylinder Briggs with manual choke is not the same as a V8 with a 4 barrel with electric choke.
I accidentally stopped the video I was recording at 1 second...so I'll just post the one from yesterday. The issue is much worse the longer it sits...after the first few failed starts ...it seems to prefer around 3/4 throttle but it will start at any throttle position except choke once it's get a tiny bit of heat into it. My original thought was not enough choke closing but that doesn't seem to be the case.
photos.app.goo.gl

Start up attempt - 10 hours parked

New item · Album by Mike Kennedy
photos.app.goo.gl photos.app.goo.gl


#33

A

artemjemmy

350Rocket said:
I mentioned above that it has this from the factory, I've been shutting it off which is why I don't know how it could flood the carb.
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You have no way of knowing that the fuel shut off is actually working anymore. I just changed an in-line fuel shutoff that was leaking last week. Sure, mine was plastic and yours is metal, but it is still definitely possible that it is leaking, especially being almost 40 years old.


#34

3

350Rocket

artemjemmy said:
You have no way of knowing that the fuel shut off is actually working anymore. I just changed an in-line fuel shutoff that was leaking last week. Sure, mine was plastic and yours is metal, but it is still definitely possible that it is leaking, especially being almost 40 years old.
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How long do you estimate it should take to empty the float bowl? It eventually shuts off and will not restart but it could be leaking a small amount.


#35

A

artemjemmy

350Rocket said:
Yesterday I shut off the fuel and let it completely run out (took like 60 seconds at least idling before it finally died - maybe the shutoff isn't sealing perfectly?) This morning I turned on the fuel and immediately tried to start it ..still the same thing, fires briefly and stalls...over and over again firing a little bit longer each time before dying. No real noticeable smoke or smell despite being in my garage. I ordered a new Chinese carb from the states so I guess that's my next attempt to fix it. I've been driving carbureted cars for 22 years since I was 16 and this behaviour seems odd to me, but obviously a single cylinder Briggs with manual choke is not the same as a V8 with a 4 barrel with electric choke.
I accidentally stopped the video I was recording at 1 second...so I'll just post the one from yesterday. The issue is much worse the longer it sits...after the first few failed starts ...it seems to prefer around 3/4 throttle but it will start at any throttle position except choke once it's get a tiny bit of heat into it. My original thought was not enough choke closing but that doesn't seem to be the case.
photos.app.goo.gl

Start up attempt - 10 hours parked

New item · Album by Mike Kennedy
photos.app.goo.gl photos.app.goo.gl
Click to expand...
So in the video the main thing I am noticing is just how slow it is running once it does start popping, and then dies. Once these engines start running, within about a second they should immediately be running up at full throttle speed. It almost seems like the throttle plate isn't open all the way. This is why I believed it had bad compression to begin with, but your 150 psi reading shows otherwise. Can you please drain the float bowl, then leave it for a while and try to cold start it with just starting fluid, to see if it does exactly the same thing? This will eliminate the possibility of any carburetor problems and narrow this down.


#36

A

artemjemmy

350Rocket said:
How long do you estimate it should take to empty the float bowl? It eventually shuts off and will not restart but it could be leaking a small amount.
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Really difficult to say, since basically all carburetors have minute differences that will have big changes in AFR over different fuel level bowl heights. I would say anywhere from 45 seconds to 3 minutes you should start to notice lean running symptoms as fuel level drops. To really be sure, can you disconnect the fuel line all together?


#37

3

350Rocket

artemjemmy said:
So in the video the main thing I am noticing is just how slow it is running once it does start popping, and then dies. Once these engines start running, within about a second they should immediately be running up at full throttle speed. It almost seems like the throttle plate isn't open all the way. This is why I believed it had bad compression to begin with, but your 150 psi reading shows otherwise. Can you please drain the float bowl, then leave it for a while and try to cold start it with just starting fluid, to see if it does exactly the same thing? This will eliminate the possibility of any carburetor problems and narrow this down.
Click to expand...
Will do that next. The weird thing is after multiple attempts it eventually comes to life like a switch turned on and it revs up quickly. Then it has plenty of power for mowing and towing once it's warmed up a minute or two.


#38

A

artemjemmy

Also, I will be honest in that I highly doubt 150 psi is possible on these engines, so I somewhat doubt that compression reading you showed. Nothing personal, but that number just seems significantly too high.


#39

3

350Rocket

artemjemmy said:
Also, I will be honest in that I highly doubt 150 psi is possible on these engines, so I somewhat doubt that compression reading you showed. Nothing personal, but that number just seems significantly too high.
Click to expand...
The cylinder would still have had some of the oil and transmission fluid I squirted in....so it would have been probably somewhat inflated by that. But I'm thinking that would typically only make a difference of like 10-20 psi usually.


#40

B

bertsmobile1

Cylinder compression in PSI is roughly 14 ( atmospheric pressure ) x the compression ratio
So 150 / 14 = 10.7:1
very few mowers run better than 9:1 unless they are EFO engines and computer controlled .
Most are in the 7:1 to 9:1 for OHV and 6:1 to 7:1 for side bangers
Some of the older ones are as low 5:1
So 150 PSI does sound more like an error than an accurate reading


#41

A

artemjemmy

bertsmobile1 said:
Cylinder compression in PSI is roughly 14 ( atmospheric pressure ) x the compression ratio
So 150 / 14 = 10.7:1
very few mowers run better than 9:1 unless they are EFO engines and computer controlled .
Most are in the 7:1 to 9:1 for OHV and 6:1 to 7:1 for side bangers
Some of the older ones are as low 5:1
So 150 PSI does sound more like an error than an accurate reading
Click to expand...
I agree with this. I think since the air is being heated as it is compressed the actual pressure produced for a given compression ratio (assuming the air in the cylinder is at atmospheric pressure to begin with), could possibly be a little higher, but yeah there is no way you could hit 150 psi. That pressure is what modern car engines with compression ratios of 10:1 make.


#42

R

Richard Milhous

bertsmobile1 said:
Cylinder compression in PSI is roughly 14 ( atmospheric pressure ) x the compression ratio
So 150 / 14 = 10.7:1
very few mowers run better than 9:1 unless they are EFO engines and computer controlled .
Most are in the 7:1 to 9:1 for OHV and 6:1 to 7:1 for side bangers
Some of the older ones are as low 5:1
So 150 PSI does sound more like an error than an accurate reading
Click to expand...
Gauge pressure for isothermal compression should be about 14.7 * (compression ratio - 1). Minus whatever is lost from valves and rings. At cranking speeds, a compression gauge will read close to isothermal compression. 150 psi would indicate >11:1 compression ratio. Which is a damn lot for a small engine, even with perfect rings.

Carbon buildup can increase compression ratio.


#43

3

350Rocket

bertsmobile1 said:
Cylinder compression in PSI is roughly 14 ( atmospheric pressure ) x the compression ratio
So 150 / 14 = 10.7:1
very few mowers run better than 9:1 unless they are EFO engines and computer controlled .
Most are in the 7:1 to 9:1 for OHV and 6:1 to 7:1 for side bangers
Some of the older ones are as low 5:1
So 150 PSI does sound more like an error than an accurate reading
Click to expand...
I've seen inaccurate readings before but they always had read low due to leakage at the valve...also this formula must not apply to car engines since they typically get around 150 psi with 8.5:1 CR, and about 130 psi on my 8.0:1 V8? I believe the camshaft also affects the "dynamic" CR? I'm not trying to argue with it, just want to understand since I've seen a ton of compression tests on automotive engines and didn't understand why small engines had so much less (and also aircraft engines it seems). I'll see if my friend can lend me his tester again and I'll redo the test and if I get the same I'll throw it on my Oldsmobile...if the previous 130 becomes like 170 clearly the gauge is bad.
The other possible cause is major carbon buildup. I had an 89 Chevy Caprice with 535,000kms on it. 9.3:1 CR 305 had 150 psi on 6 cylinders and 180 on the last 2. My guess was carbon buildup on those 2.


#44

3

350Rocket

artemjemmy said:
I agree with this. I think since the air is being heated as it is compressed the actual pressure produced for a given compression ratio (assuming the air in the cylinder is at atmospheric pressure to begin with), could possibly be a little higher, but yeah there is no way you could hit 150 psi. That pressure is what modern car engines with compression ratios of 10:1 make.
Click to expand...
1980s V8 engines in good health make it with 8.5:1 CR. I have less experience with newer engines but likely the increase in compression ratio is also accompanied by higher lift cam profile which probably offsets the higher compression giving a similar dynamic compression ratio. It's been a long time since I read up on this so hopefully I'm explaining it right.
Edit: I researched it again and it's only the intake valve closing point that has an effect (as far as camshaft profile) along with the static compression, atmospheric pressure, oil temperature, cranking speed (my battery was just charged up and it cranks extremely fast), whos compression tester you use, and many other factors. It sounds like it isn't a real reliable or consistent test anyway and a leakdown test is a better indicator of engine health. I would almost bet my compression test was a fluke and I could check it tomorrow and get 110 or something like that. Either way I'm not worried about the engine health at this point. Hopefully the new carb fixes the cold start issue.

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#45

A

artemjemmy

350Rocket said:
1980s V8 engines in good health make it with 8.5:1 CR. I have less experience with newer engines but likely the increase in compression ratio is also accompanied by higher lift cam profile which probably offsets the higher compression giving a similar dynamic compression ratio. It's been a long time since I read up on this so hopefully I'm explaining it right.
Edit: I researched it again and it's only the intake valve closing point that has an effect (as far as camshaft profile) along with the static compression, atmospheric pressure, oil temperature, cranking speed (my battery was just charged up and it cranks extremely fast), whos compression tester you use, and many other factors. It sounds like it isn't a real reliable or consistent test anyway and a leakdown test is a better indicator of engine health. I would almost bet my compression test was a fluke and I could check it tomorrow and get 110 or something like that. Either way I'm not worried about the engine health at this point. Hopefully the new carb fixes the cold start issue.
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Your last sentence says you bought a new carb. Did you do the starting fluid test like I said or no?


#46

3

350Rocket

artemjemmy said:
Your last sentence says you bought a new carb. Did you do the starting fluid test like I said or no?
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I haven't had a chance yet. It needs to sit overnight and I leave in the dark for work in the morning. For the price of the carb I figured I should get it ordered ASAP so I might have a chance to put it on before it's so cold that it wouldn't be worth doing. (not going to adjust it for cold weather usage). I will do that test next chance I get but I've got a ton of jobs to do around the house before winter unfortunately.


#47

3

350Rocket

artemjemmy said:
Your last sentence says you bought a new carb. Did you do the starting fluid test like I said or no?
Click to expand...
The closest I had to starting fluid or gasoline was a bottle of mass air flow cleaner (labelled "very flammable" so I used that tonight as I needed the tractor to move some sod with my trailer...it still took several tries but definitely fired off quicker than by itself. Not sure if it would have been different with actual gas or starting fluid. As usual it ran great after I got it going.

I also forgot to turn off the fuel tonight and when I remembered a couple of hours later it hadn't dripped any so I must have fixed the leaking needle and seat when I removed the bowl and sprayed all of it with cleaner.


#48

3

350Rocket

artemjemmy said:
Your last sentence says you bought a new carb. Did you do the starting fluid test like I said or no?
Click to expand...
Finally an update.... broke the choke cable installing the new carb and the new one is different than what was on there..... couldn't figure out why it was still not wanting to cold start when I manually operated the choke and throttle....tried it again today in near freezing temperatures and it became immediately apparent. Oil and smoke puffing out from the head gasket when I crank it. It must have been sealing up with heat from combustion until the temperatures got colder.
So I will be getting the engine completely resealed this winter since it's otherwise in good health.


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