Yamaha TRX850 Enthusiasts Forum

Hi All, just wondering if someone can tell me the stock jet sizes for an Aus delivered TRX?

I've dropped in a K&N filter supplied by our very own Mincehead, & I'm missing a bit of power down low. I had the bike tuned with the standard air filter about 6 months ago, I'm thinking they may have leaned it out a bit down low...

Thanks in Advance!

Personally I recall a small gain in response from 1500/2500rpm utilising the K&N filter... I just had the std carbs rebuilt to std jetting with a std air filter and dyno result of 76 hp(76,000km) with std headers and staintunes with restrictors removed.
This was fitted only a few weeks after the rebuild and tune not 6 mths...
Oviously a noticable difference when you change between the two filters is it??
I just pulled the pilot jet aand pilot air out but could not read what was written on them even with a mag/glass
I noticed when I fitted the FCR's upon removing the airbox and fitting the bellmouths the only jetting change was the pilot jets.

It was quite obvious from dyno results that the needle jetting reworking was dealing with the midrangle power as such..

Thanks for the info, yeah it is noticable, but the wrong way at the moment!

Doing some searching on here, K&N usually gives good results without changing the jetting, that's why I'm thinking it might be a bit lean.

Hmmmm, does sound like it MV.
Try tweaking the mixture screws in half turn increments, going for a wee ride each time to see if you can `feel` any difference.
The TRX does generally tend to be set up a tad rich, even on stock carbs.
Obviously the K&N being less restrictive will allow the motor to `gulp` a little if the taps opened too quickly, CV carbs do tend to lag at times.

Pilot screw is at 2.5 turns now, which should be in range, unless the jets have been changed...

I'm getting all all kinds of variation on the standard pilot jet sizes from 37.5 to 45... I haven't opened it up to see what's in them at the moment, but by all accounts standard jetting should be fine.

Actually 45 does seem to touch upon a memory, that could well be the size MV.
You can actually play with your mixture screw until you get the response better, it`s a bit of trial and error stuff really.
The K&N really shouldn`t have made much of a difference low down to be honest, you sure the airbox is seated properly at the two rubber flanges onto the carbs?

Didn't change anything on mine, did you use the grease that came with it? I left it off on mine, still didnt make any noticable difference, but then it was running rich. keep tweaking on the Dyno.

Dave E

IIRC 142.5

Could be few issues, I guess.

When I went to my local K&N "specialist" to get the grease they didn't know what the hell I was talking about, so I just used some silcone spray to seal the air filter, that's what they recomended...

I've tried between 2 & 3.5 turns on the pilot screw, in half turn incerements, didn't seem to help much. Does the pilot screw have as much adjustment as changing a jet size? Or less?

I checked all the rubbers & fittings when I put the air filter in, so it's not that.

I guess I'd better just pull the carbs down & see what jets are in there, maybe go up one on the pilot. Good excuse to give the carbs a clean anyway!

The `grease` is predominately to help the element slide into the slot in the air box housing as far as I`m concerned MV.
The element itself shouldn`t be greased it would destroy it`s properties altogether!

Thanks Mince, should have explained that better, it also seals the sides so that air has to come through the filter.
Grease is part number 11285-1

Dave E

Thanks for the info & the part number guys, I'll order it by number if I need it next time.

The silicone spray was only to get the filter sliding, I wasn't even going to bother with the grease at all until I tried fitting it dry! It's a bloody tight fit

so wouldn't vasoline petrolium jelly do the same job as a suggestion instead of forking out dollars for K&N grease.. Its a lub and would surely help seal it for sure and oviously petrol based so prob would not break down. I used it to lube the slides on my MKII amals on my Bonnie to stop them from sticking Worked a treat,best way around the problem I found did that for yrs

Yep absolutely Cobba, vaseline has MANY uses.