(first quote)- So it is possible to completely rid the bike of the shutdown back fire?

Maybe.  The issue is that when you shut the engine off it stops the spark from occurring in the enigine - but does not stop the flow of fuel or air through the engine.  While the engine is slowing down it is pumping air and fuel into the hot exhaust.  The hot exhaust system heats the air/fuel mixture in the exhaust......and if the mixture reaches a temperature that will ignite it......POW!  An engine that is running lean makes the exhaust pipe much hotter and more prone to igniting the mixture, an idle speed that is high provides more fuel/air in the exhaust during shut down (this is why letting out the clutch may help as it slows the engine down and pumps less fuel/air into the exhaust), and the speed at which you have been riding and the outside are temperature can affect it as well.

Getting your bike to run less lean and at a better mixture ratio may change your "POW" to a POOF" like my bike sometimes makes.  I am not a fan of getting the mixture too rich and sacrificing mileage to get rid of the "afterfire".  If you let the engine idle for 10-15 seconds, let the clutch out to slow the engine down as you shut the ignition off......maybe you can cut down the loudness or frequency of the backfire.   I have also found that quicker shifts while riding reduces the backfire during upshifts.

oh i had no idea that the back fire was from excess air/fuel igniting in the exhaust! i thought it was from compression left in the chamber and the bang was just the release of the pressure.   looks like ive got more to learn about this ole bike then i thought!!  

my idle is already at a "higher" speed i can turn it up a good amount more but then it seems way too high for an idle! ill try it out though, anything to get rid of that darn bang or at least soften it up a fair amount!

THANK YOU!

ill get back to you and let you know if that solves the gunshot!

So I opened up the mixture screw a little more (3 turns out total) and it did greatly reduce the bang more of a poof now. but i feel i might be running too rich now? it seems to not have much power when i turn the throttle past 3/4. it climbs in speed but not as fast as when im going from 1/2 to 3/4. and this morning on my way into work the engine cut out twice on decel and it felt alomst as if i was running out of gas. and it woudlnt start back up for a few min unless i pulled the choke out. and I have never had to use the choke before that.  

verslagen1 wrote on 07/11/12 at 08:32:05:



That brass idle mixture screw is a jet?  

I dont see how it could be a lean issue if im 3 turns out? i thought that made it richer?   maybe im confusing mixture screws here.

and yes i did readjust the idle speed.  i turned the brass screw out in 1/4 turn increments and tested out for decel and power down back fire. after i reached the third full turn out the power down back fire was pretty much gone.

the only time ive ever used the choke was this morning and it was only to see if that would help start it after the engine cut off because it wouldnt start up with out it. then i un-choked it right after and rode to work.

im getting the raptor petcock sometime this week so hopefully that helps!

rfw2003 wrote on 07/11/12 at 09:30:33:




The only thing that noticably got better was the shut down pop was very quiet if it popped at all! thats all i was trying to accomplish by messing with the idle mixture jet.

The best bang for the buck option is to get a Harley Dyna muffler and rejet the carb to match. The exhaust tone will be much better and it will sound like a motorcycle instead of a Briggs & Stratton. It isn't loud enough to cause problems and the performance increase makes it worth doing anyway. There is a thread here somewhere about which Dyna mufflers are bolt on replacements, as well as how to rejet the carb to work with the Dyna.

Also, the last post on this thread was over 8 years ago so some of the information that you have read may be outdated now.

Fast 650 wrote on 08/23/20 at 00:05:16:


Yes, I read about the alternatives, but my inquiry is regarding drilling holes in the baffle plate.

Being that the question is related, I saw no point in starting a new thread and beginning the conversation from scratch. Most of the threads that I found regarding this topic were about the same age and older.

New information and results will certainly be welcome.