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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12047
Experience:  25+ yrs. experience
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I have a Yamaha 1978 xs750 that I've been trying to fix up.

Customer Question

I have a Yamaha 1978 xs750 that I've been trying to fix up. I got it started however as soon as it fires up the engine revs up to 4000-6000 rpms while idling in neutral. What does that mean? Can I fix it?
Submitted: 1 year ago.
Category: Motorcycle
Customer: replied 1 year ago.
I tried restricting air flow through the three filters (it's a triple) and that seemed to work but after about 3 mins of idling it revved back up and then shut off
Expert:  Louie replied 1 year ago.
Hi and welcome to JustAnswer,
Thank you for the question and your patience. Should you still need assistance for information purposes only...
Initially, proposed preliminary checks (if have not been tried):
• carefully remove the sparkplug;
• check the burn color of the ceramic at the tip end;
• results would indicate:
- if black/sooty, then rich and/or vacuum leak issue (most likely);
- if light brown to whitish, then lean and/or an air leak concern (least likely);
• check if the tip is wet with fuel;
• results would indicate:
- if overly wet, then fuel delivery issue; check the carbs, linkages, throttle cable (likely).
Please post back results / observations of the above once tried.