426 carb problem

8 replies to this topic
  • kubamtx

Posted July 22, 2007 - 10:41 AM


Today I decided to clean my carb.
I've took the carb off, cleand ,made BK mod, put it into the bike.
Then I have adjusted my BK screw to 0,2 sec but I flood the bike during adjustment.
I tried to start it and it started but after milion kicks and hot star...
It was popping even when iddling I've took a short ride and It was ok on higher revs but popping horribly when deaccelerating.Very ansmooth work on idle.
Could you tell me what's going on?
I've checked pilot screw and it was 1,75 turn out.
During cleaning I turned the pilot screw out and there was a spring and washer and I don;t know wich part was first in the carb but I think it doesn't metter in this case.

  • grayracer513

Posted July 22, 2007 - 01:03 PM


It does matter. From the bottom, there is the screw itself, then the spring, then the washer, and then there is a small O-ring to seal the screw. The screw pushes on the spring, which pushes on the washer, which puts pressure on the O-ring to make it seal to the carb body. If you have lost the O-ring, this may be your problem.

  • kubamtx

Posted July 22, 2007 - 01:30 PM


Thanks I'll check this but I know that I was looking into this hole and there was the o-ring, then I put the washer and the spring so ok.

But I'll double check if there is the O-ring tomorrow

Another thing is: Is it possible to put this flat plate which is on the slide up-side down? And how the bike goes then?

It starts only on hot start and imidietally dies. I have to kick with the hot starts and immidietly close the hot start. Then the bike can idle but it's popping even on idle.

  • grayracer513

Posted July 22, 2007 - 04:06 PM


That is entirely possible, and a very common mistake. When you look at it, it looks like it should go with the curved edge down, but that is exactly wrong.

It belongs with the curved side up, and the small hole in the 6:00 o'clock position.

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  • shanedut

Posted July 23, 2007 - 07:45 PM


When i did the bk mod to my bike i had to go up one size on the pilot jet too so if all the other things are ok i would start with the jetting. Start with your fuel screw and slowly turn it out if you get it out more than 2.5 turns and its still popping go up one size on the pilot and try again.

  • Raider9170

Posted July 27, 2007 - 06:10 AM


my money is that you put the slide plate on upside down. I did that a few years ago and it did the EXACT same thing. Grayracer...... why is that plate removable with the rubber in it and the hole in the bottom??? I have always wondered.

  • grayracer513

Posted July 27, 2007 - 07:35 AM


It's there so the slide will seal to to the carb bore. The slide itself is on rollers so it will operate smoother, and be less prone to sticking, and so that there will be less wear to the carb body in the long term. Floating the slide in the bore like this, however, means you either can't have the slide seal to the carb body, which wouldn't work, or machine the fit very precisely, which would last only until it wore a little bit. The answer is a lightweight plate that floats in the back of the slide.

  • Raider9170

Posted July 27, 2007 - 09:29 AM


I understand. What about the fact that it is "hollow"? Is that weight savings? Also, why the hole in the bottom of it? Is it a metering issue or something??

  • grayracer513

Posted July 27, 2007 - 10:25 AM


The hole is there so the slide won't need to open as far to achieve an idle as it would without it, which has to do with the way slide throttle carbs transition from closed to open. The form is probably just a product of engineering the plate for minimum weight/max strength/durability.

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