QuestionMy 97 Yamaha big bear 350 is well maintained and low hours/miles. It used to have excellent torque in all gears but now has no bottom end. When I'm climbing a hill (especially with a load) or in mud I'll find myself bogged out suddenly and have to shift
all the way down to first gear to get the engine to rev way up in order to continue. I've changed plugs, cleaned the air filter, checked all manifold clamps, had the carb apart (no evident varnish or green) sprayed carb cleaner throughout. It starts and idles well, doesn't seem to smell rich, and doesn't burn any oil. It just doesn't have any torque any more.
Should I rebuild the carb? Is the valve lash set wrong? What should I do to get my torque back?
AnswerHi Randall,
I suspect the main jet vibrated loose. Check the carburetor and see if the main jet in the bottom of the float bowl. Clean the carb while at it.
Read the spark plugs. They can indicate problems with the air-fuel mixtures in the carburetor, and about what's occuring during combustion.
Measure cylinder compression and perform a leak-down test to determine the sealing properties of the combustion chamber (condition of the engine).
Valve clearances and cylinder compression must be within service limits before the carb will work properly. Measure valve clearances and adjust accordingly.
If you need further assistance, send me your email addres as requested in my instructions. I'll return tech files to you via email.
Respectfully,
Mark Shively
