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Old 06-25-2011, 01:57 PM   #34
New to Seattle
Joined: Mar 2010
Location: Maple Valley, WA
Oddometer: 10
'08 DR650 w/ FMF-Q4, K&N, Jet kit. Need help tuning.

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.
'08 DR 650
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