Questionfirst off, I understand you don't really deal with ATV's but let's speak generally as a "4stroke" question. This 2000 model 125cc 4stroke 4wheeler made by Carter Bros. runs ok driving it in circles around the yard, but if you go 50yds or so it starts a sputtery backfire and will eventually die if you keep. Going long enough. I just bought me and my son dirtbikes and my daughter this 4wheeler and I feel terrible that hers won't work. Any ideas of what causes backfirring like that in a four stroke ???? Anything would be helpful.... I'm a 2stroke man so I'm outta my element here. Thank you so very much!!!
AnswerAdrian, 4 stroke engines back fire from either the exhaust or the intake.
Backfiring in the intake and dying on full throttle or prolonged acceleration sounds like it is running out of fuel to me or has a bad air leak on the intake side.
It is 9 years old, so has been sitting a long time, I imagine. You have to go through the whole fuel system from the gas cap vent hole to the bottom of the float bowl and clean everything. I have no idea of what kind of carburetor it has, so it is hard to be more specific about carburetor settings.
Once you know that the fuel system is clean, check the intake manifold for any air leaks between the carb and the cylinder head.
Also, have someone check the valve clearances. If the valves are too tight, they will not close fully when the engine heats up and cause compression problems.
Check the fuel tank petcock screen for blockages, while you are checking out the fuel system. Sometimes gunk builds up in the bottom of the fuel tank and restricts fuel flow to the carb.
Bill Silver
