Comments for My vintage two-stroke Yamaha idled really fast then died

Contact

Comments for My vintage two-stroke Yamaha idled really fast then died

Mar 07, 2012

Yamaha R5 or RD or what?
by: Judy

You need to be a lot more specific. I own nearly a dozen vintage 2 stroke Yamahas, from an RD60, RD125 to two RD350s and two RD400s, along with a couple RZ350s. I've worked on them all for a couple of decades and may be able to help.

The larger bikes (350+) have Mikuni VM28 roundslide carbs, which are pretty simple ones. If you email me more information, when I get back home after caring for my Dad I can email you information from the Factory manuals. Unfortunately I'm stuck out of town for awhile, hopefully not more than a few more days.

If you bike's idle suddenly shot up to redline unexpectedly, that's usually caused by a slide sticking. The slide is a round piece that the jet needle sits in the middle of. The slide can stick if the throttle cable binds up. If the slide doesn't return to the bottom and has remained stuck, the carb cannot operate properly to start. If you want to learn just how it operates, I suggest going to the Sudco/Mikuni website and ordering their manual on carb jetting/tuning. It allows you to make sense of how each part of the carb has a play in idling, lower speeds, middle speeds and top end, based on the position of the throttle when each part of the circuitry (pilot jet, needle jet/jet needle/main jet comes into play for fuel flow and how they overlap.

Here is a link to the website where you can order the carb manual. It's only about $10 or so. Money well spent:

http://www.sudco.com/manual.html

BTW if you tap on the carb bodies the slide might unstick itself, if that's the problem.

Sorry I can't help you more right now, but if you want to email me you can do so @ Quicklimegirl@hotmail.com. and I can get back to you when I return home, hopefully soon.

Click here to add your own comments

Return to My vintage two-stroke Yamaha idled really fast then died.

Return to Ask (or answer) a Question CLOSED.