1995 Yamaha RT 100 - Revving high non-stop...



RT 100

2 Stroke


My RT 100 is staying revved all the way up once cranked.  It kicks just fine, cranks in 1 to 3 kicks, compression seems good (top end was just rebuilt), and carburetor is brand new.  I premix 32:1 (the oil pump is not used).  

I have ridden the bike with the new carburetor.  I had the revving problem then too, but was able to adjust the carburetor until the idle was good, and rode it fine in the back yard, slowly for a few days.  

Then, my new throttle cable/assembly came in, and installed it, and the bike has been running only at high RPMs since.  The bike just is wide open when cranked no matter what I do.  The slide doesn't seem to be sticking; I have watched it go up and down, and it looks fine.  Below are a few other things I've tried.


I've tried: 
*adjusting the idle screw and the air screw.

*put a brand new throttle cable and assembly on (the cable is loosened as much as it can be).

*RTV'd the gaskets outside the reed valve going to the cylinder (I thought the bike was sucking air there).
*checked the spark plug (the electrode is brownish black and the body is wet).
*fuel is flowing and is in bowl.
*no obstructions in air filter (practically brand new).


So, anybody have any suggestions?

Thanks :thumbsup:


sounds like a 2 stroke  runaway ?


things that cause this are air leaks  past the carb and even in  the case / base of cyl head etc


and fuel issues   sometimes you need to get the carb and lines primed ,,  but it reads like you did that

and you ruled out the slide so a  WOT throttle  / carb prob is  out

Edited by Zimman

Did you ever find out what was wrong with your rt100?  I have a RT180 doing the same thing.

This happened to my RT180, last year. It was my throttle cable. I ended up lubing the cable from the top & bottom. That fixed it for me.

My RT100 will not even start now.  I put it up in the shed and haven't looked at it since last Summer.  I have a '79 XL250s that I am working with right now, but I plan on breaking the RT back out in the next month or so and seeing if I can get it to turn over.

If it's a round slide carb check the brass alignment pin. It's usually midway up on the side of carb, they can get pushed out and no longer make contact with the slide groove.

Thanks, JBFL, I will check that out.  The bike is running now, but is still running wide open.  The throttle cable seems fine, and the slide is moving up and down.  I also recently learned that when the choke is ON that the bike doesn't rev as high.

Edited by StigzArmour

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