# 21hp B&S



## dynodon (Nov 20, 2009)

Hello all, 
I'm new to this forum. I thought I'd give it a try to help solve a performance problem.
I have a 21hp B&S lawn tractor that runs rough, and then runs smoothly with the choke partially closed until it's under load and well up to normal operating temperatures. I have always maintained clean oil and clean fuel system. Each season I install new plugs,air filter and fuel filter.
Regretfully I've lost my onwers manual... The carb does not have the adjustable main jet as with older models...but instead has an electronic (?)two wire connector plugged into the bottom of the float bowl ?? where the adjustable main jet would have been? I normally use 89 octane and a fuel stabilizer during winter storage (inside). The mower ran fine all summer but just started this problem as I was ending the last of yard work for the season.
Spark plugs indicate an uneven color. The left bank indicates fouling or an overrich mixture. The right plug shows very clean burning. I switched the plugs (left to right and right to left) and the same colors are present. If I pull the left plug wire off at idle...the engine will keep running. Reverse the process...pull the right plug wire off at idle and the engine will eventually slow and stall? I haven't tried a compression test yet...sorry 
Can't think of anything else to add to this...Will greatly appreciate any suggestion.


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## 30yearTech (Sep 14, 2006)

Model, Type and Code numbers would be helpful.

I would suggest checking the valve lash on both cylinders. 

You may have an issue with the carburetor not feeding fuel on the side that's not running good. The part on the bottom of the carburetor with the wires coming out of it, is an after fire solenoid. The solenoid just restricts the flow of fuel through the main jet, when you turn the ignition key off.

You could also have a weak or failing ignition module on the side that giving you problems.

You should be able to find an owners manual for your engine at the Briggs web site.


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## dynodon (Nov 20, 2009)

Whoops? Here's the engine data.

MOD: 407777

TYPE: 0167 E1

CODE: 011029YG


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## terry82 (Dec 3, 2009)

i would pull the plug wire off.put a spark plug on the end of it .now try to start.look at the spark in the spark plug. is it the same on both sides?i use seafoam in all my motors once a year


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