Setting Mikuni Carbs - Snowmobile Forum: Your #1 Snowmobile Forum

zipper670 · 01-22-2008, 05:49 PM

My ’97 MXZ 670 is running a little rich, is setting the carbs a big deal or should I get a dealer to do it? I am mechanically inclined but I have never set Mikuni carbs before and I have no any factory settings to go off. If anyone has any advice or any spare manuals, they do not need anymore that would be great.
P.S It has twin carbs.

**smallengineguy** · 01-22-2008, 08:10 PM

The first thing to find out is it running rich at idle, mid range or full throttle? There are different adjustments you can do for each. Some reading for you:

http://www.motorcyclecarbs.com/carbs101.pdf

zipper670 · 01-22-2008, 08:59 PM

Thanks for the article –smallengineguy- that really helped me out. Just a few extra questions:
* How do I set only one carb at a time?
* There is one adjustment screw on the belt side of each carb, where is the jet needle?
* How do I set the idle? It is currently idling at 1100 and should be running around 1800 from what I am told, correct?

* Finally, would anyone have factory settings I can try for basis point, to get me on the right track?
Thanks again.

**smallengineguy** · 01-23-2008, 07:43 AM

Idle is set with the LARGE brass screw on the side of the carb. Turn BOTH carbs equally so idles are the same. The slide needle is the long needle when you remove the slide from the carb. There is a clip that should be in the middle slot on the needle. The air bleed screw is on the side of the carb, kinda diagonal, toward the engine. it had a slot for a screwdriver to go in. That should be one turn out from closed, but you'll need to adjust it a quarter either way to get the best results.

zipper670 · 01-23-2008, 09:18 PM

Thanks again for the helpful info, still running rough at idle to ¼ throttle though. I am going to clean everything again and make sure it is for sure the pilot jet. If I have to change it, how do I know what size to get?

snoeproe · 01-24-2008, 09:47 PM

what makes you believe your motor is running rich?
have you done any throttle chops and checked plug color or piston wash?
if your motor is stock, i'd leave the stock jetting in it.
your carbs are clean with clear pilot and main jets, correct?
make sure your air screws are in the correct position first, then set your idle to spec.
then make sure each carb is opening at the same time when you push the throttle (sync). if they aren't in sync with each other, adjust the cable accordingly to raise or lower the slide.
then make sure each carb slide is open all the way at WOT, if they are not open all the way, adjust the cable accordingly.