Valve clearances?

[bagmaker]

The pick ups for the inductive ignition. Is it a harmonic problem around the pick ups once things heat up tollerences close or harmonic vibration causing movement around those stated revs where the problem comes into play.

Replaced the pickup, and the stator, same issue remains.
There could be substance to what you say if there is play in the main bearings causing the crank/rotor to move.
I can't feel any play, it all sounds tight enough when running -hey some gravity here, its not a quiet engine at best- with no significant knocks or clunks.
But OK, loose flywheel issue could account for it. JohnKTM suggested the woodruff key along the same lines.

On my list

Hey Cobba, can you eleborate more?
I still have this problem, virtually nothing left to replace (even put another wiring loom in) -what would I look for?

[cobbadiggabuddyblooo]

Reading back over your post, You had the head off and reseated the valves... Yes???
After riding you found the tollerence had closed on a valves somewhere, Yes???
Have you had the head off again to check if that valve is burnt and no longer sealing properly??
This sounds like the culprit to me...
Is it an early model TRX head pre '97????

[bagmaker]

Reading back over your post, You had the head off and reseated the valves... Yes???
After riding you found the tollerence had closed on a valves somewhere, Yes???
Have you had the head off again to check if that valve is burnt and no longer sealing properly??
This sounds like the culprit to me...
Is it an early model TRX head pre '97????

Its a '97 model.
I have had the head off 3 times during this saga, the symptoms are the same as tight valves as you say. "Head off" time #2 included professional grinding and seating. The last assembly I put it together at maximum tolerance and she has a nice rattle to keep me satisfied.
I have done compression checking and all valves seem to be sealing well.
During all this, and despite ALL the modifications and checks, the problem has remained identical to when it first started except for one thing, its slowly getting worse!

[blackone]

Did you try it without the thermostat?

[ekoja]

Mate... let me say from the outset that I am not a TRX guru of any description ...but there was a thread on here where the threader (is that even a word) had similar problems, whereby it would run then not run blah blah, similar symptoms, notably the cooling of the exhaust was also the case.
Turned out to be a kinked fuel delivery hose of some description. The other thing that came to light was that an inline fuel filter that was fitted (I don't know if yours has one as I have not read the whole thread) was not delivering enough fuel.
Then again...
All the best with it, you are a man of considerable patience. I think by now if it had of been me I would have tested the bike to see how well the bastard would burn.

[cobbadiggabuddyblooo]

You know if you become a guru Ash, you can prob get away just wearing your turbin and not a helmet on religious grounds.

[bagmaker]

ya, I have considered other ignition to solve the problem (light the whole f">:_+$%^ thing up!) And just flogging the thing on Ebay.
Now un-employed, that might be the way to go

Thanks Ekoja, did think fuel starving for a while, Mr Yamaha having no concept of how to run hoses and all..
My Fuel line currently sports a loooong spring internally to stop the kink, flow has been checked as "heaps" whilst problem actually occurring.
I never considered exhuast pipe cooling -has anyone experienced anything like this?
Also removing the thermostat, does anyone run without one? Might be a bit too cool here sometimes but -what am i missing regarding removing it?

Thanks again all, summer coming.

[Con Rod]

this really sound like a fuelling issue to me rather than an electrical one. That it runs ok cold but gets worse when it heats up is an indicator as is the difference in cylinder temps. Cylinder temp suggests a lean mixture on the hot side. Do the plug readings show one lean and on rich?

Were I looking to diagnose and resolve I would first off make sure I have not kicked fuel or vacuum hoses.

Then I would look at the carbs to make sure all the jets are clear and the are set up identically for float height, needle height, main jet and pilot screw.

I would make sure I dont have anything like an extra o-ring in the pilot screw or some such.

Next up I would check the inlet rubbers to make sure there are in good nick and not perished or letter in air.

[M.V.]

ya, I have considered other ignition to solve the problem (light the whole f">:_+$%^ thing up!) And just flogging the thing on Ebay.
Now un-employed, that might be the way to go

Thanks Ekoja, did think fuel starving for a while, Mr Yamaha having no concept of how to run hoses and all..
My Fuel line currently sports a loooong spring internally to stop the kink, flow has been checked as "heaps" whilst problem actually occurring.
I never considered exhuast pipe cooling -has anyone experienced anything like this?
Also removing the thermostat, does anyone run without one? Might be a bit too cool here sometimes but -what am i missing regarding removing it?

Thanks again all, summer coming.

Hey mate, I have one of Cobba's ignitions fitted, if you wanted to grab my original to test on your bike you're wlecome to. (assuming you haven't ruled this out already)

[bagmaker]

ya, I have considered other ignition to solve the problem (light the whole f">:_+$%^ thing up!) And just flogging the thing on Ebay.
Now un-employed, that might be the way to go

Thanks Ekoja, did think fuel starving for a while, Mr Yamaha having no concept of how to run hoses and all..
My Fuel line currently sports a loooong spring internally to stop the kink, flow has been checked as "heaps" whilst problem actually occurring.
I never considered exhuast pipe cooling -has anyone experienced anything like this?
Also removing the thermostat, does anyone run without one? Might be a bit too cool here sometimes but -what am i missing regarding removing it?

Thanks again all, summer coming.

Hey mate, I have one of Cobba's ignitions fitted, if you wanted to grab my original to test on your bike you're wlecome to. (assuming you haven't ruled this out already)

Thats fully nice of you MV, thanks but I have tried a replacement box (after having the original tested, been told its OK and still not believing the experts $ouch) and made no difference. I wonder if a cobbernition would do any good?

[bagmaker]

Con Rod thanks, replaced the carbs pretty early in the debarkle, thought FCRs would fix it

problem same as old carbs.


sounds better though, more poke too

[cobbadiggabuddyblooo]

The pick ups for the inductive ignition. Is it a harmonic problem around the pick ups once things heat up tollerences close or harmonic vibration causing movement around those stated revs where the problem comes into play.

Replaced the pickup, and the stator, same issue remains.
There could be substance to what you say if there is play in the main bearings causing the crank/rotor to move.
I can't feel any play, it all sounds tight enough when running -hey some gravity here, its not a quiet engine at best- with no significant knocks or clunks.
But OK, loose flywheel issue could account for it. JohnKTM suggested the woodruff key along the same lines.

On my list

Hey Cobba, can you eleborate more?
I still have this problem, virtually nothing left to replace (even put another wiring loom in) -what would I look for?

I'm having a stab in the dark on this one. I know harmonics can do some strange stuff sometimes with resonant frequencies.
I remember talking to the crank balancer on this subject and he was telling me about tests GM had done by removing the balancer shafts on one of their motors to gain more power by having less rotating mass.
But there was no real gains because the resonance with the shaft removed was actually breaking apart the atomised fuel/air molecules and creating issues with burn rate.
I even noticed with the 2lb difference trye pressure and vibrations beginning to manifest through the bars .. all to do with resonant frequencies once again.
I may be wrong on this one but just looking with an open mind..

[Con Rod]

Con Rod thanks, replaced the carbs pretty early in the debarkle, thought FCRs would fix it

problem same as old carbs.


sounds better though, more poke too

sure, but the fact that you changed the carbs means nothing if its running rich.

Warm up the bike, ride for about 20 minutes and then when you stop at lights or such, blip the throttle, see if it immediately returns to idle or hangs for a moment just above idle and then drops

Also see if it drops below, and then rises


I mentioned the inlet rubbers as well. If they are not sealing right they can cause no end of frustration. They may look fine but still be leaking. If they are old and have not been replaced I would suggest replacing them. Replacements are not expensive

[bagmaker]

Con Rod thanks, replaced the carbs pretty early in the debarkle, thought FCRs would fix it

problem same as old carbs.


sounds better though, more poke too

sure, but the fact that you changed the carbs means nothing if its running rich.

Warm up the bike, ride for about 20 minutes and then when you stop at lights or such, blip the throttle, see if it immediately returns to idle or hangs for a moment just above idle and then drops

Also see if it drops below, and then rises


I mentioned the inlet rubbers as well. If they are not sealing right they can cause no end of frustration. They may look fine but still be leaking. If they are old and have not been replaced I would suggest replacing them. Replacements are not expensive

Could be right but I reckon inlet rubbers are going to leak hot or cold
I am pretty convinced its electrical (uh oh, theres words to look back on) - the style of miss is too "sharp" ie, the stutter stops too cleanly in the rev range. Rich running tends to blubber and cough before coming good, this is a sharp-edged "missing cylinder" and suddenly "firing cylinder"
The carb wasn't just replaced -they were both replaced with FCRs from standard carbs. Initially these were running very rich, now they are slightly rich but pretty close. Through all the carb changing the symptoms have'nt changed AT ALL - you would think if a fuel issue those symptoms would vary a bit with different style carbs, different jets, different filters, etc.

[alextrx850]

Another good running bike is the best way bags.
Swap carbs, coils, ign, wiring ,switches.....until it comes down to the engine itself.
It's gonna be something WTF .