11HP Briggs and Stratton, gas blowing out the carb!

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Old 04-14-09, 10:38 AM
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11HP Briggs and Stratton, gas blowing out the carb!

I've got a Briggs and Stratton 11 HP L head (horizontal) on a mower I'm trying to fix.

When I check the valve clearance at 1/4" past TDC I have the correct clearance .007 (aluminum block), however, during the ENTIRE compression stroke, the intake valve is open a few hundreths and it's blowing the fuel out of the carb. How could this possibly work? How could the engine ever NOT blow its combustion mixture out of the carb?

I've heard of a easy-start system that releases the compression when rpms are low (during crank) but I'm not sure if this engine has that. I pulled it off the mower and opened up the bottom end, and I don't see any mechanism in there that would do any such thing. Also, I thought those mechanisms worked on the exhaust valve. Anyway, on the cam, I only see the two regular lobes.

I've checked to make sure the flywheel key is in good shape, and the two dots on the cam are lined up the way they should be.

HELP, I don't know where to go from here!

Model 252707 Type 0621-05 Code 91081611.

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Old 04-14-09, 10:38 PM
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The easy spin setup does hold a valve open a little, and I think that's all you're seeing. On those engines, it's not a mechanism...it's just the grind of the cam lobe. How much compression does the engine show, and will it start if you put some gas into the cylinder? Is the spark plug wet? Maybe getting too much fuel?
 
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Old 04-15-09, 06:35 AM
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Originally Posted by cheese View Post
The easy spin setup does hold a valve open a little, and I think that's all you're seeing. On those engines, it's not a mechanism...it's just the grind of the cam lobe. How much compression does the engine show, and will it start if you put some gas into the cylinder? Is the spark plug wet? Maybe getting too much fuel?
I did some more research last night, the easy spin, from what I can tell is only used on the exhaust. Then again, I was reading a pretty generic briggs manual that covered a bunch of different types.

I don't have the equipment to check compression, but I can tell by spining by hand and watching what the valve does, that the intake doesn't close until near the top of the compression stroke. Where on the compression stroke should the intake valve close? Shortly after the stroke starts, and not near the top, right?

Also, good theory about getting too much gas, I'll have to experiment. I'll have to put the thing back together first of course! Is there a starter fluid aerosol that I can spray directly into the intake and leave the carb off? (just thinking out loud here, that would be an easy way to diagnose a carb problem, eliminating it)

Yes the plug was wet, but I assumed that was normal when a motor doesn't start.

Thanks Cheese! I'll have some tinkering to do tonight!
 
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Old 04-16-09, 08:40 AM
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Originally Posted by oilstain View Post
I did some more research last night, the easy spin, from what I can tell is only used on the exhaust. Then again, I was reading a pretty generic briggs manual that covered a bunch of different types.

I don't have the equipment to check compression, but I can tell by spining by hand and watching what the valve does, that the intake doesn't close until near the top of the compression stroke. Where on the compression stroke should the intake valve close? Shortly after the stroke starts, and not near the top, right?

Also, good theory about getting too much gas, I'll have to experiment. I'll have to put the thing back together first of course! Is there a starter fluid aerosol that I can spray directly into the intake and leave the carb off? (just thinking out loud here, that would be an easy way to diagnose a carb problem, eliminating it)

Yes the plug was wet, but I assumed that was normal when a motor doesn't start.

Thanks Cheese! I'll have some tinkering to do tonight!

Wasn't able to get any work done, my garage flooded! Hopefully today I'll get some time.

I'll let you know what happens.
 
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Old 04-20-09, 07:04 AM
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Originally Posted by oilstain View Post
Wasn't able to get any work done, my garage flooded! Hopefully today I'll get some time.

I'll let you know what happens.
Alright!
I threw it back together and tried to start it with just the starter fluid. It wanted to kick over.

I leaned it way down (rebuild kit is coming) and got it to run!

Thanks so much Cheese!
 
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Old 04-20-09, 11:10 PM
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Great! Glad I could help! Thanks for the update.
 
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