becoming crazy with WR360's mikuni tm

[piede90]

Hi all, I have a '98 Wr360 with mikuni TM 38 stock carb, it was too rich so I checked the jetting, this was the situation:

main 340 (brand POLINI)
pilot 27,5
needle 6AEJ03-64 1st groove

from the manual I found the standard jetting for this bike is the following:

main 430
pilot 40
needle 6AEJ03-64 2nd groove

so only the needle was correct, but the main and pilot jets was leaner than the std, but the engine runned rich, so it was strange...

I trusted the manual and bough a 430 main jet, 40 pilot jet and a new needle thinking the old one could be worn

the first thing I noticed was the old pilot jet is broken...



but the stranger thing is the new needle is longer than the old one... it is crazy! they are the same needle, both of them have the same code impressed over the body, both are genuine MIKUNI parts with the autenticity mark... I can't found an explanation...



I think they have also a different conicity, but I'm not sure about this..

I tried the bike with new jets and both the needle, the pilot jet run well, at low throttle opening runs well, a lot better than before, but from middle to full throttle it is a disaster... worst than before, too rich, at full throttle is almost unusable with the engine that struggles to take more rpm...

why the standard jetting won't run ok? even assuming the old part are weared, now I have all new, where can be the problem?

and why 2 needle that should be identical are so different?

I know the better choise is to throw away the mikuni and put a keihin PWK on it, I have plenty of jets and needle for keihin, so it would be easy to find the correct setting, but I can't buy it now and I want to use it with the mikuni carb for now...

thanks to all

 

[Trenchcoat85]

how is the bike mechanically? (reeds, crank seals, rings, manifold, plug, etc)

is the needle jet oblong or worn?

regarding your old needle: did someone file the tip off (maybe after it broke)? the taper (conicity, i guess) of both needles looks similar, but the lighting in the image is a bit weird so it's hard to tell.

without the emulsion holes in the pilot, maybe you were drawing too much fuel.

if this bike is relatively new to you, it might be better to put a different carb, it seems like the current carb has had some issues. OTOH, if you've had the bike for 20 years, maybe you're ok.

btw, the only 2-strokes I have nowadays are chainsaws... so my knowledge is kinda decaying. And your english is spot-on; if you have a problem with anything i said, lmk and i'll translate from american to english.

good luck.

 

[NCSteve]

You may just have carb problems, but before you go crazy at least do a compression test. Unless the engine is fresh you could have other issues that make jetting the carb difficult.

 

[troy deck]

IF ITS ALL MILK AND HONEY FOR STARTING AND LOWEND AND UP INTO THE MIDRANGE THEN LEAN OUT THE MAIN SWEDISH HUSKYS WERE ALL WAYS RICH UP ON TOP IM SURE THE ITALIANS ARE THE SAME WAY BET IT CLEANS UP NICELY

 

[Trenchcoat85]

oh yeah, one more thing: make sure the other part of the pilot jet is not still stuck in the carb.

 

[troy deck]

oh yeah, one more thing: make sure the other part of the pilot jet is not still stuck in the carb.

yea be damn sure of that of course if it is the new one won't go in so... now you know

 

[justintendo]

my 95 with stock pipe ran pretty decent with book spec jetting and stock pipe/silencer when running a tm...started very easy. if you are book spec i would look elsewhere until it runs good then tune

 

[piede90]

thanks to all for the aswers

I'll start to try with lower main jets, hope it works better, I was worried to lower to much because the manual... theorically with a full stock engine the standard setting should go well, but if you tell it was too rich now I'm a bit reassured

the old needle is ok, there is no sign of breaking, this thing of the two needle is umbelievable...

I hadn't checked if the rest of the pilot jet is still in the carb but the new one went in without problem so I think there is nothing inside, but the next time I'll shake up the carb to be sure

the bike is relatively new for me, I purchased it a few months ago... I plan to check the engine after summer but there aren't strange noises around the crankcase and the compression is more than ok (it's a lot harder than my '96 Honda CR250) but with the right tecnique it stars at the first shoot so I'm confident the engine is in good shape...
I surely will change this carburetor, I always had keihin carbs, so I have lot of experience and lot of spare jets for those carbs, but for now I had other outgoings and I hoped the standard carb runs a little better until I can replace it...

I tried the keihin PWM 39mm that normally is on my honda and it runs very very well, but it's a bit short and it's a pain to fit it between the two rubber intake, and the carb's bowl bump on the crankcase... maybe with a spacer under the reed cage I can put the carb backwards enough to fit it well, I'll try for sure... here is a pic of the PWM:



and a pic of the my two bikes:

 

[rancher1]

Wow, that 360 is in great shape.

 

[piede90]

thanks, I hope that doesn't hide some bad surpise.

I plan to maintain the original look, so I had to find an original headlight and since I can't find a seat or at least a seat cover from 1998, I had to buy the 1999 decals to uniform the graphics.

another thing.. I suspect the pipe isn't from the 360, it looks too short for me, I saw other 360 photos and on the left side the pipe seems to go more over the cylinder than mine, is it possibile that someone replace it with one from a 250?
to be sure I plan to buy a doma or HGS complete exhaust

 

[justintendo]

pm me about seat cover, i may have a NOS one