Question-------------------------
Followup To
Question -
I have a 1998 Yamaha YZ 125 bought used. It has recently been exhausting excessive white smoke out of the exhaust. Compression is 120. Carb adjustments done according to manual. Performance not noticeably affected. Mixed fuel/oil at 30:1 per manual. Any help or insight would be appreciated.
Thank you.
Answer -
Hi Patrick,
It appears that all is in order. Have you switched premix oils or fuel recently? What adjustments were made to the carburetor? Describe the air cleaner that's in use and it's condition. Describe the appearance of the spark plug.
Respectfully,
Mark Shively
Mark...thank you for a prompt response.
The premix oil and fuel are the same as was being used before. The carb adjustments I did were just to follow directions in the manual for the idle and pilot air screw. The spark plug was black and a little wet. Also, the crankcase oil was down a few ounces. The air cleaner is in fine shape, clean, and in proper place.
Thank you again for any guidance.
AnswerThe spark plug indicates a overly rich air-fuel mixture. This may be due to the carb adjustment, engine starting attempts, riding out of the powerband (lugging the engine), ignition problems, or restricted air intake.
Oil being low is a concern. Compression tested 120 which is decent for any cylinder (not sure of service limits for this model). I would perform a leak-down test (presure test)to check crankshaft seal integrity. The white smoke is indicative of oil burning. crankcase oil being a bit low is not uncommon, but with the smoking exhaust, I would check inner seals. Seals may be worn and leaking causing the smoking.
Send me an email and I'll return test and repair files that will assist you. My email address is: mshively1@woh.rr.com
I'll check email again late tonight.
Respectfully,
Mark Shively
