Small Engines (Lawn Mowers, etc.): Vanguard 6 hp., internal engine components, briggs and stratton

Question
I have a Briggs and Stratton Vanguard 6 hp. engine that is about 2 years old. Model is 118432 and type 0036E1. Since it was new this engine has surged up and down at full throttle and will not run at low throttle settings without having the choke partially closed. Seems to be running lean. The carb was replaced under warranty with no real change. I have plenty of experience with small engines but there does not seem to be a good solution to this problem since the carb is not adjustable except for idle air. Is there a different carb out there that will work for this engine or what is the solution?

Answer
No alternate carbs.  Looking at the parts list there is a main jet and a pilot jet.  Are your jets brass?  If so then you can modify the jets.  All you need is a carb or very small drill bit set.  Sears used to sell a small little pencil tool with very small drill bits.  I bought mine years ago.  Anyhow, use a wire gauge tool set, like welders use, to measure the current jet hole size.  Record the size.  Then drill out the jet one size larger.  Test.  If you mess up you can always buy another jet or use solder to fill the hole and re-drill like many racers and tuners do.  You shouldn't have to modify the jet but sometimes it's the only option.


Have you checked the valve clearance and made sure nothing is warped causing a very small air leak leading to the lean condition?  Do you have a leakdown tester to check the condition of the internal engine components?

Eric