Cold start issues 1981 Briggs 11hp model 25

350Rocket

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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.
 

artemjemmy

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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.
 

350Rocket

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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.
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.
 

artemjemmy

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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.
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.
 

350Rocket

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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.
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.
 

350Rocket

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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.
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...
 

artemjemmy

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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...
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.
 
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artemjemmy

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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...
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
 

350Rocket

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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.
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.
 

artemjemmy

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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.
 
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