Yamaha TRX850 Enthusiasts Forum

Just finished restoration no my TRX, test rode for over 400 Ks over last three days and running and starting great then on way home just cut out and will not start. I have cleaned carbs, plugs, fuel filter and have spark and fuel supply also checked side stand switch. Will try to start on full choke and then die. I fitted new rings and cleaned up the valves and shimmed valves with new cam chain during restoration. I have also checked all wireing connections. So am at a loss now as to the problem. Help please. Ken.

Air leak somewhere? What's the condition of the carbs to cylinder head rubbers?

Is the vacuum fuel tap working correctly? How much petrol is in the tank? If the level is lower than the carbs, check the vacuum fuel pump is working. They can be a PITA at times.

Thanks for your answers to my question. Have checked every thing again and found no problems then decided to do compression test and have next to nothing on left cylinder and 50 PSI on the right so looks like an engine out job. Can any one tell me how a bike that is starting and running just fine can suddenly just stop with little or no compression. Once again thanks. Ken.

I can think of lots of things that could cause the engine to stop working, and all of them are nasty.
Hopefully it'll be something simple and not catastrophic, but I can't think of anything.
One bright side, at least you know how to pull it apart and put it back together again.

Thanks Dicky, I may be in for a surprise when I open up the engine or maybe shocked. I am just finishing a rebuild on my BMW R65 engine and as soon as I get that off the bench I will tackle the TRX engine. Once again thank you to those that replied and I will let you know what I find. Cheers Ken.

You've got an R65?
Why??
I had one for a while and it was by far the worst handling bike have ever ridden, and my mates who rode it all agreed.
Didn't stop me from riding it too fast, but it scared the shit out of anyone following me.
The back end was all over the place.

Back to the TRX.
Did it make any self destructing noises?
Broken ring, broken piston, stuck/bent/dropped valve, cracked head...
Like I said, I can only think of nasty causes of low/no compression.
Wait, maybe it's a blown head gasket.
Did you replace it or use Cobba's hylomar trick with the old gasket?

kenbev wrote:Thanks for your answers to my question. Have checked every thing again and found no problems then decided to do compression test and have next to nothing on left cylinder and 50 PSI on the right so looks like an engine out job. Can any one tell me how a bike that is starting and running just fine can suddenly just stop with little or no compression. Once again thanks. Ken.

Overtightend camshafts, it happens.

HI Tarwetijger!

I don't think that overtightened camshafts would wait 400 km to kill the teeth of the crankshaft - after a "skilled artisan" in a free workshop did the valve clearances on my first TRX and overtightened the camshaft(s), mine made no 4 km till the teeth gave up.

Also I'm convinced that any try to start the engine would not be like kenbev described :

kenbev wrote::... Will try to start on full choke and then die. .. .

@kenbev:
From remote I can't guess a (good) reason for such a behaviour.
Nevertheless, it sounds quite severe ...

"Hoping for the best"-greets from Munich!

Update to my saga, Dropped engine oil and filter and no sign of any metal. Engine is out and w never had waiting for bench space. Dicky, I love my air heads and have never had any handling problems with my R65 if set up right with tire pressure etc. Will keep you all informed of what I find in the engine which should be done in the next day or two. Cheers. Ken.

Well engine ripped apart and found air leak on intake manifold left cylinder no gasket just goo and then found cam chain guide on ajuster side damaged and falling to bits. biggest surprise was inlet cam timing was off by a few teeth but exhaust was spot on. Sprockets look good and cam chain was new. I have checked rest of engine and all seems to be good apart from plastic bits in the sump. Cheers. Ken.

Unusual failure, but sounds like it will be recoverable.
Certainly could have been worse.

Lot better than finding nothing and an easy fix. Thanks Mate. Ken.