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View Full Version : Engine "turning on and off?"

robot_dan
03-08-2007, 04:08 PM
So a strange thing happened to me today. On the way to school, crusing at about 43 mph, I started to get a wierd feeling of a slight accelration and deaccleration, like the bike was lurching forward, then backward, then forward, then backward. I ignored this, but about half a mile later at a stop sign, taking back off, I discover I could go no faster than 20 mph.

Now, once I get to 20 mph, the engine sounds like brrrr *pause* brrr *pause* birr *pause and the bike is pulling forward, and then not pulling, and pulling forward, and then not pulling in sync to that.

It's stranded away from home right now so I haven't gotten to look inside, but I'm guessing maybe a roller slipped out of the variator, or the belt is not grabbing it right?

Any thoughts?
robot_dan
03-08-2007, 04:09 PM
by the way, I have a straight up provoscooter stage one setup, except the green malossi rollers in my variator, which I can't remember but I think might be 6 grams.
StepVino
03-08-2007, 04:50 PM
Makes sense.. you have a crankshaft on one end, gear box
at the other.. somewhere in between is the only place it could be
slipping. Did you grease anything when you put the variator on?
morevino
03-08-2007, 08:25 PM
and of corse alway check and change your spoark plug at 4$ it worth the money i had the same problem than you in the pass and it had so performence part on it so give it a shot for a new sparkplug
StepVino
03-09-2007, 06:37 AM
..Is the brrr a vibration? Not sure how that would help, just more
info.
XPS1210
03-09-2007, 11:30 AM
have you checked your plug to see if your to lean?

The stock cylinder can take a LOT of abuse before it destroys itself...

Just a thought of something I'd check...
Zuma-Zuma
03-09-2007, 05:40 PM
Did you re-jet the carb after the stage 1? Sounds like its lean...Does it bog at a hi rpm or low while at 20mph
robot_dan
03-11-2007, 12:34 PM
Update: I finally got the scoot home and took a look.

It turns out the air screw on the stock carb vibrated out, so it was completely open. That must be what was wreaking havoc on the engine performance.

Anybody know where I can order a replacement, or maybe just what diameter thread that air screw was?
XPS1210
03-11-2007, 03:57 PM
yeah.... you can get a new one from your yamaha dealer... or maybe someone will PM you with a stock carb they will part with?