I did the modification to my pipe like you did, and I really like it. You can really tell you have a V-twin under you. When I get on the throttle and let off real quick, I occasionally have a loud backfire. I was wondering if I need to make any adjustments or is this normal with this modification.

Thanks,
james

 

back out the pilot screws about 1/4 turn..it will help

 

Mine does not backfire. You are supposed to mess with the air screws like Surveyor said.

However, if exhaust can leak out of the system anywhere except the tip, it causes backfires. So, make sure you don't have any leaks. If it can leak out, fresh air will leak in on the downside of each pulse - causes backfires. I did a pretty good job making my weld air tight.


kawikentuckian650, it sounds great doesn't it! Mine is not all that loud. I don't want it louder. What size drill did you use and how many holes?

 

I used a 3/8 in. bit and I put 8-10 holes, I don't remember. Backing out the pilot screws will allow more air in I assume ? Where exactly are they, I don't have a manual as of yet.

*Father-in-law has a grizz 660 and he has the hmf set-up. Mine now sounds so much better than his, he is sick. I love to make my 650 purr when I get around him....

nyroc, they are many guys on here that seem to know much about the 650, but you seem to be the most knowledgeable that I have seen on any of the forums. Where did you learn so much: prior knowledge with v-twins, former tech, or just trial and error until its right ? I wish you were in my neck of the woods to help keep mine tuned up. Most dealers in Ky. that I have dealt with are mostly clueless.

 

The air screws are located near the float boals, on the right side of the carbs. They almost look like they are in the float bowl cover itself, because they indent the flot bowl so much. The air screws control idle mixture. The more turns out, the richer.

Lean has a tendency to misfire, sending unburned/partburned gas into the exhaust pipe. You run leanest on decel, so richening the idle lessens backfire.

People are accusing me of knowing stuff now. I have spent too much time reading posts on this and 4 other forums. If you notice I only answer things I know something about, or have read about. I have had my 650 since last august, back then I only asked questions.

 

I fiddled with my air screws eventually turning them out a half turn. Went on a 50 mile ride yesterday. Great sound and acceleration but still backfiring on let-off. I can go wide open then gently ease off the throttle and it doesnt do it. Only when quickly letting off the throttle.
Do you think drilling holes around the center exhaust hole in the back would help. Or should I just live with it. What would you do.

You can get to the pilot screws without removing anything, right? (on right side of motor under air box. They were extended out and adjusted with a small flat screwdriver) anyway thats what I adjusted out. I really need a service manual.

 

kawikentuckian650-- The manual is pretty cheap. $29.00 from the dealer, I believe. It is very good. Well laid out, IMO.
You're right, nyroc seems to be very knowledgeable of the P-650. I have picked his brain a few times. He has a great "650 website", too.

 

NYROC, what other 650 forums are there?

Thanks
Ray

 

Doh? That is atvconnection's competition. I sent you a message with a list of the ones I know of.

This one is the best (most posted) one. But, the classifieds on one of the other ones has a lot more stuff in it.

 

now, lets see, I can only tell you about what I did on my street bike, so ALL MAY NOT APPLY..take it for what it is worth..

first it is a yamaha v star 650, stock pipes, I took the rear baffle out, & the rear pipe as well, it gave it a deep sound,
but while NOT what I would consider a backfire it would burble a little on hard decel.
I think that event the stock ones do as well, but with the muffler you just can't hear it.
I turned the air screw out a little, & it made MOST of it go away, still a little burble every now and then, but doing a plug check, jetting is good.

The Royal Star v-4 1300 had the same exhaust mods done to it as well, and behaves the same.
on most of the aftermarket street bike (cruiser style) pipes they have a little burble to them.

I think that what causes it is on decel cold air gets sucked back into the pipe & causes backfire/burble when it hits the hot exaust gases, the 650 v star had a air injection system that forced cold air in the exhaust to try to burn off any richness in the fuel..
needless to say most of the owners who have aftermarket pipes or mods to stock have disabled this..

so like Roc says, if you have any exhaust leaks, it will backfire, if not probably a little burble..
in my street bikes I have found this to be true.(the main reason to disable the AIS on the v star)

hope this helps, but all in all I'd say, if you opened up the pipe from stock, richened the carbs up a tad, and are getting a little burble on decel, the plugs look good to verify you jetting, I would'nt worry about it.

Surveyor [img]i/expressions/face-icon-small-cool.gif[/img]