Yamaha TRX850 Enthusiasts Forum

Hi All,I have searched through previous posts and not found a similar problem.
On the way home I noticed that when the tacho needle got to 6krpm it dropped to zero rpm,the engine was still pulling well, I backed off throttle to lower the engine rpm, then as I got back on the throttle all seemed well. Engine sounds like it is revving at what is indicated on tacho, twist the revs up to 6k and the needle drops back to zero There is no hesitation or missfire, and will continue to rev smoothly well beyond 6krpm.
I did a check of the TPS today and the needle goes straight to 8krpm and stays there, doesn't matter where I set the TPS
After a recent rebuild of the carbs, 3 months or so ago, I had a similar issue with the TPS reading 8k on the tacho, I checked the ohm readings on the TPS but couldn't fault it. Once I balanced the carbs I was able to get the TPS to settle at 4krpm after adjustment. The bike has been running very well since carb rebuild.
Any suggestions would be appreciated.

When you put the TPS back on the carbs, did you preload it the right way ?

I don't think I did? I followed the the directions in haynes manual.I will have to read back through the procedure. The tacho has been working fine since rebuild. I haven't noticed the fault prior to yesterday and it has been over 6krpm on quite a few occassions, as you do

After paying a bit more attention to what and when the issue is actually happening. The tacho needle will drop to zero rpm once the throttle is rotated past 1/3 open. I can get the needle to go beyond 6krpm without dropping, so long as the throttle is no more than 1/3 open.
Seems like a fault with TPS sender unit or the wires between it and the tacho, will check a few things out over the next couple of days

Interested to see what you find here, im experiencing exactly the same.but have a considerable drop in power too.
Goos luck

have just installed a low klm second hand TPS, $100. Genuine yamaha unit $345 .Straight away I was able to adjust position of tps to read 4k on tacho, no more bouncing needle. Will test ride it tomorrow morning.
Back when problem started I had the tps on the bench to test ohm readings, I noticed that when I put side pressure on the rotating part of sensor I was able to get proper ohm readings, I decided to put a small wad of plastic down inside the tps and put it back onto carbs, this put a little lateral pressure on the tps, and the tacho needle stopped jumping all over the place. Instead it self analysed by showing correct rpm then 3krpm then 0rpm and back to correct rpm, just as the manual states
Through all of this I never lost power anywhere, if anything, I would assume the ignition was running on full advance, and fuel consumption seemed to be higher than usual, I normally average 17klm per litre/ around 250klm to reserve.

Sorted, good to hear.

Timings running full advanced on mine with TPS MOD and still average 270km with the FCR's.. I'm sure Rod is getting over 300km before reserve with stock carbs.

not sure what to say here cobba? 45ks round trip to work, down and up tamborine mtn, 230 corners/bends, nearly no constant throttle riding, 16/42 gearing, 95 ULP. Engine is running sweet .

Gearing answers most of that...

16|42 is quite short for the street, but great for henri roberts eh

Yes fung it is, I only use henri's on special occassions. My normal track is mystery road which eventually joins guannabah creek road, then onto maudsland road. If you were going down henri, take the first left just at the bottom of the first hill, to thee end turn ri tht, to the end of that turn right
you're now on guannabah creek road, it joins maudsland rd at the dog leg.

Hello!
I have got the same problem with broken TPS. Does anybody know what other bikes use the same type (new cost ..plenty and second hand market seem small here on trx). Found out that Yamaha R1 year 2000 does not fit (marked A1 and mirror to TRX-type). TRX type is marked A2.