Yamaha TRX850 Enthusiasts Forum

Hi
Sometimes my bike runs poorly at part throttle. Seems to miss. Open the throttle further and it picks up again. Its intermittent. I've checked the spark plugs; they're fine. Any ideas?

I'm thinking fuel issue; Maybe the carbs need a good clean?
Thanks guys.

Are the carbs fouled and dirty?
Are all your carb circuits properly tuned?
How long since a carb sync?
Are your emulsion tubes worn?
Does the problem exist warm and cold?
Does it run better either warm or cold?
Has the issue suddenly arisen or gradually gotten worse?
Have you changed anything prior to this problem?

Just a few things to think about to get you on track to a diagnosis.

Throttle position sensor on the carbs might be problematic....advance retard on the sparks
Switch ignition on...then disconnect the TPS at the sensor...wait a mo, then reconnect it, the tachometer with the ignition still on should read 4000rpm.
Adjust the TPS with the anti tamper bolts to gain the 4000 rpm reading.....if not the TPS might be faulty.
Just a thought.

Thanks STu
I'll need to take a look at the carbs and see how they are.
Ages since a carb sync so that probably needs done.
I changed the emulsion tubes a few years ago but have not done many miles on them (maybe 5-6k)
The problem exists when warm. May also be there when cold but have not noticed. I generally warm it up a good bit before riding. Its intermittent anyway.

alex; thanks for info re. TPS. Will check this too.

alex; seems the TPS may have been the prob. WHen I checked, it was at 1000rpm.
Adjusted it to 4000rpm and now it seems to be sorted, at least after a short ride, problem is not there. Will take it for a longer ride on Friday to verify. But looks good. Will try and check the carb balance too anyway.

Why would the TPS go out of adjustment?

Many thanks guys.

Balanced the carbs now too. Going great. Seems to start easier and idle better but may be just in my head!

Good to hear. Happy days.