Yamaha TRX850 Enthusiasts Forum

Ok after much wailing and gnashing of teeth and a period of wearing sack-cloth i finally got around to getting the sparkplugs out and they are grey/white. I could have sworn it was running pretty rich. How bad is it? Is there an adjustment to richen things up a tad?
Stock carbs
(fairly) free flowing exhaust
KnN filter
resistors removed from sparkplug leads.

Take each fuel screw out by 1/2 turn and richer things to see how things feel.
If just riding round locally most impact will be 1/8 to 1/2 throttle and remember the fuel / idle circuits are running all the time.
If still no real colour after a couple of hundred km’s But running ok, leave it be.
If you want a little more acceleration raise the needle from the main by 1.
Does it still pull ok in 4th and 5th gear, full throttle at 6500rpm???
Main jet size looks ok...
Educated guess that the plug closest to the inside of your hand is cylinder no.2

The pilot screw on a Trx is a fuel screw, to make it richer you need to screw it out (anti clockwise).

Cheers Dave i’ll Change that

cheers guys, so that does look lean? The electrode and the underside of the earth prong are still brown, and there is no visible wear. Bike pulls pretty good everywhere. Cant say ive wound out 5th gear yet but have had it up to about 180km a few times. Im guessing somewhere near top of 4th with a 16t front and stock rear sprocket?
I cant remember which plug is which in that photo, was going to mention it but forgot. I did mark them "L" and "R" when i pulled them out, and one is slightly different colour to the other. Also the flash made them look whiter than they are but they are pretty white. Just the top of the earth thingo though.
Might give the pilot screw a tickle tomorrow and see what happens.

The plugs look to be in good condition otherwise.
What size pilot jet is installed and how many turns out is the screw.
Remember the pilot jet only has a minimal effect after 1/4 throttle, the needle position in the slide will have more of an effect then, as will the main jet.

Thanks Dave. So, do you reckon I'm in danger of burning an exhaust valve or something the way it's going? Or is it still safe. Bike pulls pretty good and the plugs show no wear or rounded edges. Not sure how long they have been in there,, Its likely the dealer put them in about 3-4000km ago when i bought the bike and they changed the timing chain.

Probably unlikely to burn valves.
Without knowing your carb settings, it is difficult to suggest a change.
You would need to check mainjet, pilot jet, pilot screw settings, needle position in slide, float height, etc.
If you don’t have any problems with fueling at low throttle openings, adjusting the pilot screw is probably not necessary.

Cheers dave.

Just tinker with your mixture screw and make it richer. you’ll Be fine.

Looks just fine. Ethanol/unleaded fuel does strange things to plug colour

^ Thats good to know.Thanks. I've been using 98RON exclusively in the three months I've owned the bike.