Yamaha TRX850 Enthusiasts Forum

Hi

Have a problem with my TRX850 that has us completely baffled!

Got a late TRX with 7k miles on it. Previous owner had only done a few hundred miles on it since 2004. In this time he managed to start it with a cylinder full of fuel and bent a valve. This was repaired for him and then not run again for a few years.

The bike starts and runs very well. But after only a few minutes on tickover the engine is very hot. To the point you can not touch the radiator or hoses. If you hold the bike at 2000 rpm it misfires on the left cylinder. Quite a big backfire, as it feels like it would kick the airbox off

What we have done to it so far. Thermostat removed, water pump checked and it is working. TPS checked and set up. Tried another CDI unit, another set of carbs, new plugs. Had the top end off to check the valves are correct. Had the cylinders off and check the pistons, rings, etc.

Yet it still does the same. Run it on the dyno and after a couple of minutes you can see the left hand downpipe glowing red, right hand side is fine.

So just about to give up! Is the bike just a lemon or anyone got any ideas on what to change/check next?

Thanks

Hey there. That's a great job you done.
So in this case we could start with something we really know.
Left cylinder definitely runs hot:
Did previous owner rebuld this cylinder or the other?
Did you check compression and what does it say?

Can it be that you missed the timing? Did you set it "as it was"? I really think that you did it properly, but just as an idea.

Maybe there is an air leak in the intake manifold, whitch stayed there before you got the bike.

Good luck, I'm in a similar situation and I know your pain

Ditto the above. Compression check and valve clearance check. I know you say a "late TRX" - how late? Early ones (1996 build year) were renowned for inlet valves clearances closing up

It can also be handy to remove airbox and close one carb inlet by hand. Than another. Look at the difference. It helped me today to findout missyncronisation.

i have the same problem almost imposible even with starter spray to start wont idle but revs quicker than ever after about 20 seconds both pipies are glowing red hot it was going perfect before this any ideas?

Cylinder full of fuel ????? ok that happens and we all know that issue due to the down draught nature and sticky fuel float.
Would not that cause hydraulic lock if valves are closed (stress on the conrod)and if partially open the rising piston would expel fuel back through the inlet valve ????
Sump would be full of fuel/oil mixture ...
Bent valve can happen from incorrect valve timing and there is a few posts on people suffering from the same issue after having a mechanic they trust to service their bikes make a simple mistake with big consequences.