Cold start issues 1981 Briggs 11hp model 25

[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.

 

[artemjemmy]

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.

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.

 

[350Rocket]

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.

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.

 

[artemjemmy]

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.

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.

 

[350Rocket]

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.

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.

 

[350Rocket]

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.

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.

 

[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.

 

[artemjemmy]

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.

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.

 

[bertsmobile1]

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.

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 .

 

[350Rocket]

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.

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.