Hey guys, anybody have any suggestions on why my 600 is backfiring when you let off the throttle and it idles down. It also smokes a little bit when it does it to. It uses no oil, and runs fine, other than this. It does it the worst when going at a fair rate of speed, then letting it idle itself down, is usually just one backfire. Thanks

 

What color is the smoke? Sounds like it may be running a bit rich. Try cleaning the air filter and exhaust and see if it helps (assuming you've never messed with the jetting)

 

Did both of those things already. I haven't messed with the jetting, but am wondering if maybe the plug is bad, or air mixture may off. I am also wondering how to change the mixture if I need too. The smoke is dark, not white.

 

Here's a quick check to see if it's from running rich...pull the airbox lid and run it with out that for w few min. If the problem is fixed, then you are running rich and need to go down a size on you pilot jet. You may even be able to just richen up the idle screw

 

Ok, will be tough to tell though, as it only backfires when letting off at a fair speed. What is entailed in changing this pilot jet? If I end up needing to do it.

 

You will have to buy a new piolit and install it. You could screw in your air/mixture screw it lean out the idle mixture. Also make sure your filter is not blocked up and your snorkel is clear.

 

Antrim,
Mine backfires as well and has some dark smoke especially when first starting, other then that it runs great.
I'm taking mine in for its service pretty soon and hope to have it fixed.
I've heard a lot of people in here say theirs smoke as well. I noticed mine backfired only when I was going pretty fast and let off the throttle completely. If I gradually slow down it won't backfire.

 

I've got a similar problem with my KTM 620, Found it to be the valve guides in the head. Decided to put up with this as it is only a minor problem and present with many 4 strokes that are driven hard. Hope this helps a little

 

<< I noticed mine backfired only when I was going pretty fast and let off the throttle completely. If I gradually slow down it won't backfire. >>



Is the same with mine. I changed the plug yesterday, was blacker than tar. Has to be running to rich. But it quit backfiring after I did that. I am sure that as soon as this plug gets a little wear on it, the backfiring will start again. I am wondering if there is anyway to adjust the carberation, besides a new jet?

 

This is a very common problem with the big single thumpers!
The fix that I use on my 99-Grizz is very simple and effective.........
One number hotter spark plug...... premium fuel always...... and just a splash of automotive gas line antifreeze on every tank.
The puff of smoke that is noticed is unburnt fuel air mixture gathering in the combustion chamber and is usually expelled on cold start-ups.......
Try this fix and reply back to this forum with your results!

Enjoy...

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