Yamaha TRX850 Enthusiasts Forum

hi all.
up date to my last post.
im having problems with my carbs, it was suggested i mite have an air leak, so i took the carbs apart and replaced all the jets and gaskets, all the rubber inlets and pipes are good but i spotted that one of the diaphragm cover had a crack in it, i managed to find one on ebay and replaced it.
the bike now starts and ticks over but it wont rev up.
so im thinking it may down to the pilot screws, so can any one tell me roughly how many out turns.

According to the manual the standard setting is two and a half turns out. I think an issue with the PS is more likely to affect the tick over and part throttle performance rather than the problem you're describing.

markymark wrote:but it wont rev up.

Tell us more...
Do the revs increase from idle at all when you open the throttle?
(I assume you have connected the throttle cables correctly and the butterflies are actually opening)
Do they increase smoothly and then slow to a steady state, or do they increase and then stutter, pop and fart about?
When you had the tops off the carbs, did you lose the tiny little o-ring (#8 on the carb parts diagram) that sits under the front of the plastic cover?
Pilot screws only affect idle and smallest throttle opening, so if it idles this in not your problem area.

hi thanks for your reply.
the cables are the right way round.
the butterflys are opening and closing now problem.
diaphragms are ok no splits and the small o rings are in place.
the bike starts fine and tics over sweet but as soon as i try rev it, it starts to splutter.

Almost there then...
Is there fuel, obviously there's enough to idle, but is the line blocked at all? Is the pick-up from the float bowl blocked at all?
Next are the jets and the needle. Any blockage in the fuel feed to the jets will only show up when you move off idle. Carb cleaner and compressed air can help to clear/check.
What needle is fitted, and at what notch? If you've got an aftermarket needle (ie Dynojet, FactoryPro et al) then you'd do well to find the original needle and stick them back in.
The taper on aftermarket needles is almost always aggressive, allowing much more fuel to flow at small throttle openings. Having the needle sit high does a similar thing. Both cause over-rich running.
After that lot there's still the possibility of air leaks from the inlet manifold rubbers or the vacuum lines connected to the manifolds. They are connected aren't they?
These bikes are all over 20 years old and all the rubber bits are beginning to perish.
It could still be bad electrics

I've recently replaced all jets, needles, tubes etc., in mine. I used a kit from Keyster as I've also recently used the same to refurbish my Bandit carbs, with good results. However, when I ran the TRX for the first time it didn't run too well and, as dicky said, the needles were the prime suspect; once I re-fitted the original needles the bike ran beautifully.

ok heres an update.
ive fitted new manifold inlets, change the new needles back to the old ones, set the pilots to 2.5 turns, new vacuum pipes. and the carbs seem to be balanced spot on.
the bike still starts ok and idles ok, but still when i try to rev it up it still pops and back fires threw the carbs.
dont no what more i can do.

markymark wrote:ok heres an update.
ive fitted new manifold inlets, change the new needles back to the old ones, set the pilots to 2.5 turns, new vacuum pipes. and the carbs seem to be balanced spot on.
the bike still starts ok and idles ok, but still when i try to rev it up it still pops and back fires threw the carbs.
dont no what more i can do.

How have you fitted the main metering needle? Is the white plastic washer in place? what position is the clip on 1-2-3? Are the piston damper spring fitted? how did you balance the carbs?

Do you know if the valve clearances are OK?