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Old 06-26-2011, 05:47 PM   #37
Southern Explorer
sagedrifter's Avatar
Joined: Apr 2006
Location: Jacksonville, Alabama
Oddometer: 1,460
Originally Posted by TripTheNinja View Post
First of all, thanks to everyone who contributes to this website chock full of information. I've gained a lot of knowledge from here and hope to contribute where I can. I'm doing my best to do all of my own maintenance, etc. so that I can be confident of fixing anything while out in the mountains or on long hauls away from home. Hopefully this question can help others as well.

I have an '08 DR that I bought used and in mostly stock form. I'm not doing any mods that require me to crack the case.
Last month, in an attempt to wake this bike up I purchased the FMF-Q4 exhaust, K&N filter and the "ASM-Jetkit" from Procycle. I stuck to the instructions that came with the jet kit. I'm currently riding in the humid climate of South Carolina mostly at 1000 feet elevation with weekend rides ranging up to 7000 feet.

I drilled the slide and did the air box mod (cut a big hole in the top). Procycle recommends using the #150 main jet for free flowing exhaust, setting the e-clip in the 4th groove from the top of the slide, and starting with the extended idle fuel mixture screw at two turns out.

I did just that and it ran like a raped ape. Only problem was that it backfired real bad on deceleration and when switching gears. I played around with just about every combination of jets (145, 150, 155), 3rd and 4th grooves in the needle, and idle screw adjustments (adjusting from 2 turns out after 10 minutes of riding). All of the settings provide better performance from stock, however...

-The 145 main jet backfires the least (at the 4th groove in the slide) and has the least power and response. Barely better than stock.

-The 150 main jet set at the 3rd groove has the better power however backfiring a bit more.

-The 155 main jet set at either the 3rd or 4th groove run good however it smells rich in any setting.

My goal is to get the best performance with no backfiring. If it's not possible to rid the bike of backfiring I can live with it. Any suggestions?

Thank you.
Make sure your pilot jet is really clean, what your describing is a back fire or decel pop?

If its back firing at idle through the carb its the pilot circuit or an air leak at the carb boots.

If its popping through the exhaust on decel, thats normal. 2 1/2 turns out on the pilot should help in the decel popping. A 150 main jet is all you need with exhaust and a cut air box. Mine popped very little at 2 1/2 turns out while living in Florida. But, it is pretty rich, 1 1/2 to 2 turns out is better usually.

The Q4 is loud compared to stock and your probably just hearing the pop from a straight through exhaust. The Q4 is at least 10db louder and it keeps getting louder with use.
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