Mikuni TM Owners, Need Help

I've put a Mikuni TM34 on my stock 850 and can't get it leaned out enough, it is pig rich throughout the range of throttle, bad 8-stroking and sooty plugs.
Carb is new and came with:
Pilot 25
Needle 6DH3
Needle Jet 389/Q2
Main 280
Slide #4
Filter, Uni foam

I've got the needle down in the leanest position and it still soots up the plugs badly.
I'm thinking next step will be to down-size the needle jet, but there are hundreds to choose from and I'd rather not take a wild guess. All I know is I need to be leaner, how much I don't know.
I would appreciate your comments and experience with what works from your experience, especially which needle jet.
Thanks
Jaydee

The fact that your isn't perfect right from the get go is no big deal and should be expected.

Yes, Needle jet is an option along with needle but my experience is the needle jet change will get you where you need to be. I assume you have the clip in the TOP groove, the needles leanest position, and it is too rich across the board. Although the 280 main jet should be OK for an 850, I would get a 260 and 240 to have on hand. It is really relative depending if you want economy vs performance when cranking on the throttle. You will have to wait until the carb is basically set up good before you do a WOT plugchop anyhow.

http://www.jetsrus.com/a_jets_by_carbur ... mikuni.htm

My source is Jets R US, and I have used them a lot with all the test i have done. Paypal and fast.

The Q2 is really the middle of the road and you can go either way from there.
Remember, you are looking at the 389 type ONLY, not all of the others so it is not as overwelming as you might have thought.

So, from a Q2 i would skip the Q0 go down to a P8, P6 and maybe a P4.

Here another thought, I am not saying the needle you have is not OK but I think the TM34 may use a type 5 series needle.
You might want to try a 5n13 and the called for 5pf17, but try the Needle Jets first.

What ever you do, or should I say what ever option you choose, don't get discouraged. Once you get it right, it will be righteous.

If you find that the one that work the best turn out to be little lean (i realize you are talking rich, but bear with me) with the needle adjust up in the lean position (clip in the bottom groove) then there are shims you can get to put under the clip to raise it even higher, if necessary

http://www.jetsrus.com/a_jets_by_carbur ... mikuni.htm

A friend recently built a fairly radical Triumph 750 and put dual 34mm TMs on it. The TM-34 came with a Q2 needle jet, 5FP17 needle, 35 pilot and 280 main, and as you experienced, it was pig rich over the entire needle jet range to the point that it blubbered regardless of the needle or throttle position. When you look at the annular areas obtained with a Q2/5FP17 combination, it creates a relatively large area (rich). Makes one wonder if the carb might have been set-up for a 2-stroke where fuel flow occurs under a much lower vacuum condition. His final set-up was a P2 needle jet, 6DH3 needle, 30 pilot and 230 main.

I think pete.v has provided good counsel with his suggestions and perhaps only a needle jet change is required to fix you up. I'd also get a P2 needle jet (one jet leaner than P4) just to cover all bases. If you want to experiment with a considerably leaner needle you might want to try a 6FL14, which is about the leanest of the 6 series needles.

Let us know how you make out. Not that you need more sources for needles and jets, but Fox Distributing is another option.

http://www.mikuni-foxdist.com/tuning.pdf

I have a TM34 on my 75 850 MKIII

This is the jetting I have written down in my log book:

Main Jet 240
Pilot Jet 27.5
Needle Jet type 389 size P-0
Needle 6DH3 (middle)
Air Jet #2
slide 4

I have a KN filter. Which filter you have may make a difference in pilot size. I remember I purchased pilots 25-32.5 and mains up to 260. First set-up was too rich and had to tweek it down to the above settings. Depending on where you are located will make a difference because altitude will have an effect.

If you bought a boxed TM they sometimes come without the air jet so make sure you have one in there and check the size. It's located in the outer front ring of the carb I think at the bottom.

Get a hold of Bill @ Rocky Point Cycles. He'll get your jetting issues right.