QuestionI just bought a vintage 84 Yamaha Venture with 30,000 miles. The seller delivered the bike to me making a trip of 120 miles yesterday.It has a intermittent cylinder misfire and uneven idle (with vibration) but seems to clear up while accelerating a higher speeds. Freeway speeds seems fine.
I don't know what kind of performance to expect. The previous owner changed the exhaust to 2 Jardine turndown type mufflers but never changed any carb settings. He tried to sinc the carbs but didn't have the right tool. He put in a new battery. The running voltage meter was at 13.1 to 13.5 he said. The bike is quite hard starting!
The inside of the gas tank only shows traces of rust (from what I can see). I suspect carb varnish or slight restriction of the carb jet(s) or carb adjustment issues ... or rejetting? It seems to have a fair amount of power at the higher speeds but a lousy idle with misfiring. I will try to run a can of Seafoam carb cleaner thru it. After that ... what do you suggest I try? Local mechanics say there are very few carb parts for this model and most won't work on it!
AnswerHi Dennis,
I think your diagnosis is spot on, Sir.
The pilot fuel circuits are what becomes obstructed in the early stages of varnishing. A good indicator of this condition is the engine starts and runs with choke, but stalls or runs poorly off choke. Also, engine runs more normal like above 1/4 throttle openings.
Many dealerships will not service MC's older than 10 or even 5 years old. Finding parts may take time, but they're not obsolete.
Send me your email address as requested. I'll return tech files that will help you.
Standing by...
Respectfully,
Mark Shively
