2stroke

Member
Nov 7, 2001
399
2
Last weekend was the first time I took my KX400 out for a race. I had never run it before, and I was having some issues tuning in the carb. It is the stock VM36SS Mikuni unit. Stock jetting, and it was pretty clean when I got the thing, and I cleaned it very well on top of that.

It had a dead spot from closed to 1/4 throttle or so. After that it ran fine. Usually, that means the pilot jet, but it was clear...even tried a new one. The funny thing was, it ran fine with the choke on. Better then fine. Superb even. I rode a whole moto with the choke on.

So i guess a richer mixture did the trick so to speak. Then again, with the choke off, it ran ok if you could ge past the dead spot.

what about this: The slide. It was missing from the bike when I got it, and I put in another mikuni slide that I had laying around. I know that slides come with different cut outs. Could a cutout be wrong enough for a bike to cause that dead 1/4? (come to think of it, I had better check what side the cutout is on! it could be a slide from a reverse carb with the idle screw on the other side. I ran into that on one of my triples---had the odd slide in the wrong carb and the cutout was facing the cylinder!) :yikes:


It ran so nice with the choke on, I may fix it in that position if it comes to that. The plug was fine, and it did not over heat or anything, but I wuold like to find out just what is going on here.
 

2stroke

Member
Nov 7, 2001
399
2
the slide thats in there is a 2.5 which is right in the middle for the VM36, so I dont see that doing it.
and the cutout is on the right side.......


yeah, I may order an assortment of pilots, I only have a few new ones, and none larger.
 

Britt Boyette

Member
Aug 16, 2004
280
0
Go over to the CR / KX / RM / YZ (2-Stroke) Discussion section and check out the jetting links posted as a sticky. There's a lot of good info to be found over there. :cool:
 

BadgerMan

Mi. Trail Riders
Jan 1, 2001
2,479
10
Air leak?
 

jason33

Member
Oct 21, 2006
655
0
check the vent tubes-
i also agree on the reversed slide- i know what your talking about-lol double check that
bigger pilot possibly-
the jet needle also moves from closed- 1/4 to wot-
 

2stroke

Member
Nov 7, 2001
399
2
Hmmm.
Will check the intake again, but its pretty solid. No floating idle or revving like you would get with a case leak. Could be some fuel circuit in the carb is clogged, but I doubt it. Im gonna pull it off again and go thru it. bypass port maybe.
The good old super tuning manual suggests the pilot and the slide cutout to be the places to make the changes..... I suppose I will rule out air leaks and clogs and then start in on the pilot, etc.
 

2stroke

Member
Nov 7, 2001
399
2
Ive been building bikes for 20 years. I dont need that kind of statement from you.

Even though I am no engineer, I am confident this slide is quite suitable for my application.
 
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