Yamaha TRX850 Enthusiasts Forum

I'm beginning to loose patience. I've done my valve clearances, double checked the valve timing, changed the emulsion tubes, set the float level, put the original emulsion tubes back in, checked the float level again, checked the pilots and it still runs crap. I've had the carbs off, stripped and rebuilt 5 times now. There'll be a cheap trx going for sale soon.

At least it starts easily now. It runs fine on the choke, but once I take the choke off, it starts spluttering. Tried it last night again (after putting the carbs back on yet again) and it only ran on one cylinder again (the left header was cold)...left plug oiled up...took it out, cleaned it , put it back in again, same story again; running on one cylinder.

Yet when I put a plug in the plug lead and hold it against the engine there's a good spark visible.I wasthinking there was nothing wrong with the ignition, but maybe I'm wrong about that. I cant see what else I can do on the fuelling side.

Has anyone got any suggestions on possible ignition faults?

I'm not real smart with this stuff , you say the left plug is oiled up or is it just wet from fuel , have you tried changing the wiring to the coils and swapping the spark plug leads to see if you can move the problem to the right plug , if that doesn't do anything then change over the plugs you never know until you eliminate the easy things . If it is oiled up then do a compression test , others will know better than I

Thansk bob. Compression test reveals 180 psi in each cylinder....a little high but within spec. I've tried new spark plugs.
I'll try swapping the coils and leads next. I just hadn't done it yet because I convinced myself it was a fuelling issue.

I'm kind of clutching at straws, but its doing my head in!!

What revs do you get when on full choke? Could be you have an inlet air leak - split or twisted inlet rubbers.

I had the inlet rubbers off and gave them a good clean. No problems. I also replaced the two vacuum lines coming from the inlets; one for the diaphragm pump and the other for the fuel cock.

By the way, where the fuel supply line connects to the carbs, there's another pipe (same diameter) joining onto the carb behind (underneath) the fuel supply. This is just a drain or a vent, right? Because the other end is not connected to anything??

...sorry youngy; when on full choke; cant remeber what the peak revs are, something like 4000 rpm maybe and sounds and runs fine at this speed.

correct - it is a drain/vent, not connected.

have you run the bike on prime? does it make a difference?

what mains are fitted?

have you tried a fuel feed directly to the carbs, eliminating the tap and pump?

I'll check how it runs on prime this evening. Then i'll try it bypassing the tap and pump and see what happens. didn't note the main jet size, but that couldn't be the problem as i haven't changed them and i had no probs before. but no doubt i'll have to take them off again.

The more I read this the more it sounds like the problem I had with my emulsion tubes. When you ride off of choke, If you keep the revs above 4000 does it runs fine, but if left to go under 4000 revs will bog down, and heaven forbid it stalls then It will not start until you have changed the plug? New plugs and will start fine. Can you post pics of the emulsion tubes you have taken out ie the originals, and what have you replaced them with, see other posts re jet settings for different tubes and needles.

Dave E

trix wrote:There'll be a cheap trx going for sale soon.

Maybe you bring it to a mechanic? In the end it saves you time=money!

yes slow codger...sounds similar. I got it running this evening a bit better but i hadn't really changed anything. It runs at 3500 rpm on full choke. It wasn't running great and both exhausts were smoking like bastards. I took both plugs out; the left one was black and sooty but dry, the right one was wet looking. Obvioulsy rich??

The tubes I took out looked like this;




When I put in the factory pro ones, it ran worse. Maybe I'll try the factory pro ones again, now that I've reset the float heights. Bloody hell, I'll have to take the carbs apart again.
youngy; i tried running it with the fuel tap on prime...made no difference really. Haven't yet tried it with pump and fuel cock bypassed.

..thanks for the ideas/suggestions guys! keep 'em coming!! as I'm not really sorted yet!

Don`t really know much about this kind of thing...but what exhausts do you have?,are the carbs set up for the pipes?
Have you tried taking it for a thrash?what`s it like afterwards?

I remember a guy on the old forum had carby problems and it was the carb body cracked.
Also ignition faults can somtimes mirror fuel starvation faults. Good luck.

The bike has standard pipes with baffles removed, but its been running fine for 3 years (good smooth power, fuel consumption a good as the best I've read on here) and I didn't change anything.

Slow codger; its got some of the symptoms you describe; i.e shite low speed running; then one cylinder goes down and you cant get it back on untill you take the plug out and clean it. Was yours really "jerky" when riding at part throttle? The smoke is a new thing, at least I never really noticed all the smoke on previous tests! White/grey smoke, but I don't think I'm losing any water. The exhaust smells petroly too.One thing I noticed was there was no washer underneath the needle when I took the jet needles out. The haynes manual says to watch out for the washer when removing the needle. There is a washer on the top of the needle (the clip in the groove) and a plastic spacer underneath this, but no other washers. Its not obvious from the diagrams in the manuals if there should be a washer there or not and I haven't been able to establish on this forum if there should be a washer there or not either. However, as I said, it ran fine before now. If the problem is the emulsion tubes, maybe the washer definitely needs to be there when I put in the unworn Factory Pro tubes? When I put in the Factory Pro tubes , it would not run at all below about 2000 rpm. As soon as I took the choke off it just died. It was like it was too lean with the Factory Pro tubes.Maybe if there was a washer underneath the needle it would richen it up a bit at part throttle?

DOBBO; I'd imagine if the carb body was cracked I'd get a fuel leak? Anyway; I've had the carbs off numerous times now and certainly didn't notice any cracks.I agree with your comment about ignition probs. The only thing is, I'm getting a good spark when I hold the plug up against the engine. I've tried changing the plugs to no avail.