QuestionBike idles roughly, slight hesitation at low RPM
acceleration. Checked spark plugs and the #2 & #4
are fouled (smelled gas and blackish ) I checked for spark and got good fat bluish spark. I did a compression test and got the following results.
#1=125psi, #2=82psi, #3=123psi & #4=85psi.The two
front cylinders read a lot lower than the two rear cylinders.I also tried putting a bit of oil into the cylinders that were low in compession and got a high comp at 135psi, Whats the problem?
AnswerHi Rusty,
From the limited information provided in the description, I suspect the problem may be a variety of causes. I would need to be present and perform several checks to accurately determine the source(s) of the problem(s).
Cylinder compression is too low on 2 & 4 cylinders. I suspect worn cylinders, vlave clearances out of service limits, or worn/defective valves.
For best results, check compression with engine at operating temperatures. Use a quality compression test tool. Cheap tools yield innacurate test results. Open throttle wide open during the test. Crank engine until gauge needle stops moving, but avoid cranking longer than about 10-15 seconds to prevent starter motor from overheating.
Next, perform a cylinder leak-down test. This will determine the sealing properties of the combustion chambers by measuring air pressure in percentage. Defective or excessively worn parts will allow air to escape. A hissing sound can be heard and help determine source of air leak/faulty parts.
Reference the poor idle/acceleration problem. Cylinder compression and valve clearances must be within service limtis for the carburetors to work properly. That's why a good tech always checks compression before performing a tune-up or other work.
It's also possible that the carbs need cleaned and/or tuned, too. It would be fruitless to spend the time and cash to fix carbs if the cylinders need repaired.
Respectfully,
Mark Shively
