Yamaha TRX850 Enthusiasts Forum

Had my Rex stood up over the winter and the battery went flat. I charged the battery for a few days and it came back up. I started the bike, it was a bit reluctant but started and once warm ran and revved fine. As it got hotter it started to idle rough and hesitate when revved. It got worse and started to back fire when the throttle was snapped open. Eventually it cut out and would not start again.
I put this down to fuel and carb trouble, i drained the fuel, replaced the carbs but it still has the same issues. It will start on the button when left to cool down, rev and idle fine, then run rough back fire and cut out. It ran fine before i laid it up for the winter. Any ideas?

Is the choke mechanism sticking on? Someone else here had that problem, some grease solved it..

Does it smell overly rich when warm?

Valve clearences.

Lectrickery connections furred up.

Carbs have been changed/cleaned etc, so no not a choke sticking.
From what i have read valve clearances close up and cause starting problems, it starts no problem, plus it was fine before it was laid up so i can't see that being a problem.

Thanks for the input though.

Nob wrote:Lectrickery connections furred up.

Yes that's my thinking, it did get a bit damp. Think a strip down and good going over is the plan for this weekend.

Battery. Put a volt meter on it. It has to be up to spec.

Hope it is something simple like damp electrics but I had similar problems it started from cold, idled, I could ride it a mile or so but as soon as I closed the throttle and slowed it would die and refuse to start until cold again, the expansion was holding the inlets open slightly.

perhaps check that the fuel tap is closing fully and not trickling down via the vacuum side
cheers
fung

All good points guys, i'll check it all this weekend

Hi.
Please let us know what the problem was.
I have an old S10 that does the same - runs like a dream when cold, but after 15-20 minutes it can't idle anymore - sounds like the left cylinder sets out (misfiring). I had hoped it could be some moisture in the ignition, but fear it's the valve clearences - hell of at job to adjust the valves !

mine is doing the same mate , then it would not start atall , took the new plugs out and they were black with and spark was very weak . have cleaned them and put them back runs ok but im sure its overfuelling (black plugs=running rich im told ) . it also spits fuel up the left side carb if anyone knows what that might be i'd be happy to hear it

Have a read of this Cloutiedumplings: http://www.factorypro.com/tech/carbtune ... gines.html If your's is running rich then this may help you work out what needs altering.

Cloutie,

If your carb's are spitting fuel, my first guess would be a sticky float valve (especially if it's been laid up over winter with fuel in the floats). Carb strip and clean job I'm afraid. On bikes with more easily accessed float bowls, an "easy" remedy to stop it dropping fuel would be to tap the float bowl with the butt end of a screwdriver.

Cyclone,

Mine's running rough as well, starts up OK on the choke, but won't idle when the chokes pushed back in, and runs rough when warm. It has been suggested that the valve clearances are looked at (and I'm probably going to rebuild the carbs while it's off the road as well).

Jobs a good un!
Changed the plugs..old ones were corroded to hell, but the electrodes looked OK Ended up taking the rad out to get the old plugs out.
Removed the coils and gave them a good clean. Mounting screws and the earth lead were corroded. Looked to me that the coils were mounted the wrong side of the frame?? Cleaned and refitted the coil earth lead and fitted new screws. Removed all the block connectors and gave them a good soak in WD40. 0nly a couple of connector looked a little manky, but the old girl fired up and ran great Gave it a quick blat up the road and it was pulling like a rutting Rhino! The Harpoon cans sounded awesome

On another note i also sorted the engine rattle. I was convinced it was the cam chain, so i loosened the adjuster back a few turns and re-tightened it...no more rattle. Looks like the tensioner was not fully adjusting.