Yamaha TRX850 Enthusiasts Forum

A while back I asked about what maybe causing the vibration I've got in my bike. I still haven't sorted it and maybe I just being over sensitive to it.

One thing I do notice though is it mimics the resonance of the carbs/exhaust, obviosly the resonance is matched to the revs, lately though the cavitation I hear coming from the carbs seems to be getting loader. Is there any imediate response for that condition?

Yesterday I lifted the tank, hooked up a longer line so I could run the bike with it tilted upright and took the air box off. When I started the motor and raced it a bit the roar coming from the throat of the carbies is huge and awesome. Underpants expanding actually! Is this normal? The other thing I noticed is the throttle slide flutters as the revs are building then smooths out when you get up close to 8000. Can someone tell me what is going on there? I know the slides work on a vaccuum set up but I thought it would have been smoother. It seems to have trouble balancing when the motor is playing catch up with the throttle opening.

I also seem to be getting a louder bark coming from teh repacked stock cans. It had a nice note when I bought the bike but seems to have been growing into a real bark more like a bigger set of cans would give. Weird.

Are these classic symptoms of needing a good service. I just did spark plugs and checked valve clearances are they are excellent. Cams are showing little signs or wear too so pretty happy there. Should I get a carb overhaul done. I was going to put the Factory Pro emulsion tubes and jets through it as a matter of course. The spray didn't look neat down the throat of the carby.

?????

The mikunis need the air box to create a still air effect. The flutter is what happens when you run without one. Sounds like your repacked cans are settling in. Totally normal. The vibration your experiencing could be chain adjustment, check for tight spots. Rex's are super sensitive to that and throttle freeplay.

How's your fuel consumption? If it's poor then most likely your emulsion tubes are worn and replacement would be beneficial. If it's ok then leave the emulsion tubes alone.

Slide rattle is normal on a downdraught carb - this is what causes the wear in the emulsion tubes - due to poor vacuum at low revs. Higher revs and better vacuum stops the rattle (flutter).

Thanks for the suggestions. I'll check the chain adjustment, which was mentioned before and maybe on the weekend I'll pull the emulsions tubes out for a look see and check that everything inside the carbs is fine and dandy.

I've posted before that when I fitted my FCRs with K&N can type filters I experienced a very noticeable pressure wave at certain RPM which actually hurt my ears unless I wore plugs... I'll leave them out and just fart my way round town with an occasional blat to wake up the dozy pedestrians, but plugs are a necessity for long runs...

G