Yamaha TRX850 Enthusiasts Forum

In a nutshell, I have got a spare TRX as my other one has done 220000km and I am a bit worried that it might expire soon.
I have put in new standard needles/tubes and it was running OK for a few km (10's not 100's) now it rough idles, is rough in the mid range, but runs OK at freeway speed.
Before I replaced the needles it ran even worse and had some aftermarket needles that looked wrong and weren't clipped correctly. Maybe pilot jets?
And the tacho jumps around approx 500rpm jumps, also the lights flicker at idle (when it does idle) maybe TPS and/or voltage reg?

My other bike runs perfectly so I can swap bits across, but I don't want to waste effort swapping bits that are unlikely to fix it.

Maybe there's more than on problem.

Anyone got some pointers on this?

At idle, if you have the choke on does it idle steady?

First off I would balance the carbs. If they are out it will run as it does now

I would first off clean the float bowls and then adjust the fuel screws to 2.25 turns out

I would put the needles on the middle clip.

Your main jets should be 142.5 from memory but that wont be the problem

You can test your TPS by turning on the ignition, unplugging the TPS and ten plugging it back in. If it is set correctly the taho needle will swing to 4500rpm.

If you still have a problem I would look at valve clearances

2 second job..just check you side stand switch is not sticking as if it's sticks half way it could be causing an intermittent signal . This earths your ignition signal

What's the battery voltage when running?

check n maybe clean all earth contact points. Might even find a loose one. +1 for checking the voltage input to the battery while running to check reg.
But for me sounds like a bad earth.

gordo-

OK, solved 90% of the problem, on the way home from work I thought maybe carbs were lean so I pulled out the choke, then engine nearly died so I pushed it in again (this was all at approx 60km/h) then the bike ran smoothly, I think something in the choke mechanism must have been jambing, even though the choke appeared to be off, it was still on. SO now the idle is smooth. Still a bit of roughness at light throttle.

Bike runs pretty smooth now, but not as smooth as my other bike, so I will balance carbs/check the pilot screws.

Anyone got any good ideas on how to turn the pilot screws? They are pretty hard to get at.

Still got the lights flickering at idle, headlight goes very dim when the indicator flashes. Will test the voltage and clean the earths when I get a chance.

Taco still jumps 500rpm, at any speed so on the freeway can't tell if its doing 4000 or 4500 at 120. Will do the TPS test this weekend

Thanks for the suggestions.

brenyw wrote:
Anyone got any good ideas on how to turn the pilot screws? They are pretty hard to get at.

the easiest way is to lift the carbs off the inlet rubbers, setting the idle screw with the bike running involves a small screw driver, patience, small hands and dexterity

Con Rod wrote:

brenyw wrote:
Anyone got any good ideas on how to turn the pilot screws? They are pretty hard to get at.

the easiest way is to lift the carbs off the inlet rubbers, setting the idle screw with the bike running involves a small screw driver, patience, small hands and dexterity

Agreed, I take 'em off too, as although I have small screwdrivers, I have limited patience, the hands of an oaf and the dexterity of a caveman.

measured the voltage at the battery:
Idle=12.85V
1500rpm=14.0v
3500rpm=14.1v
Seems that voltage ramps up between idle and 1500rpm.

Can't find a spec on this, anyone know what it should be?

Tightened the terminals on the battery (one was quite loose) and the headlights & tacho are better behaved now.