Yamaha TRX850 Enthusiasts Forum

Hi all, I'm new to the forum. love the bike had it for years. Only one issue and that is the extremely rich running. I have changed all the jets ,needles & emulsion tubes,this cured the bad running at constant throttle through town, and it also returns 75mpg at 80mph on the french motorways. It doesn't cut out at all and pulls clean all the way to the redline in top. But is still really sooty & you can smell unburnt fuel if you are behind. Do I come down on main jet size or live with it. My main concern is bore wash. K&N air filter is new and clean, plugs have about 5 thou on them,end cans are ART.
Any suggestions regards Smiffy.

Drop down to a 137.5 main some even go down to a 135.

Is the bike a JDM export or European bike?
If it's a JDM you will get over fuelling on acceleration due to the accelerator pump and this will last for a few minutes. If not, as Brian said drop the main jet down from the factory 142.5, the jets are available in 2.5 increments. I went with 140 on my Ozzy bike and 137.5 on the JDM bike. They still pull great and the over fuelling has reduced to almost nothing, I did need to wind the idle jet out a little on the JDM bike but after checking the plugs and giving it a good thrashing it's still well with the fuelling ball park. When this Covid19 crap is over I intend to put both bikes on a Dyno just to map the fuelling.
Cheers
Rod

I tried running 136's but it was ludicrously lean with new emulsion tubes and needles, cross winds would have the bike barely able to pull the skin off a rice pudding due to the way they can force more air into the system and it felt down on power the rest of the time. I was afraid of holing a piston the whole time. Afterwards I went with 140s which were better, then as the tubes wore again it got even better. Personally I can see why Yamaha went with the 142.5s, better safe than sorry. It also became a bike that I wouldn't take into town because the temperature gauge was always aiming for the vertical!

They like to be rich, the 5 valve head does nothing to help have a clean burn, I say just live with it

Many thanks for your replies, think I shall be opting for the 140's and see how it goes.

Mine was choking anyone following me. I changed carb needles and jets and no difference at all. Later I checked my valve clearances as overdue . Previous owner sold me bike at around the due mileage to be checked. And I didn't get round to doing it till 2 summers later. All inlet valves were at lower limits or slightly under. Re shimmed and suddenly no more complaints from my followers when I asked them. So it appears valves were being slightly held open when engine hot and causing excess fuel from exhaust. Hope this helps.