New 650R mods installed and have problems

My brother just installed a Power-Up kit and a Big Gun Race exhaust system. He rejetted to a 178 main provided by baja designs. When he restarted the bike it was backfiring just above idle and on deceleration. It also has a dead spot at 1/4 throttle where it will buck/jump/miss, and then it will hesitate reving to WOT from that point. He changed the pilot jet from a 65s to a 68s and he said it seemed to help. He also turned the idle air screw out to 2 3/4 turns and said that it was a little better but any further and it made it worse.

I think he needs to go richer on the pilot. What do you guys think?

Did he remove the plastic pop outs from the air box? What parts were included in his power up kit? Also he may need to recheck his slow jet (68s) and make sure nothing is partially plugging it.

Did he install the new jet needle? What clip position?

That jetting will give you plenty of fuel, at sea level, down to around 60 dgrees. The symptoms sound lean. The needle clip should be down 3 notches from the top. If it is, I'd check for lack of fuel flow (petcock screen ?) or an intake air leak.

I'm going out on a limb b/c I'm not sure your Alt or riding temp but I think its running too rich... almost like its flooding out...did he try the 172 or 175 before trying the 178? If it was me I'd try one of those before trying bigger pilot, (68s should be fine) if it is completely uncorked...(all pieces are removed from airbox, and the carb insulator).

I'm at 300ft and ran 30'F winters-thru-90'F southern humidity heat and if I remember correctly (b/c it was 3 years ago and I run the edelbrock now so I haven't had to think about jets in a while) but I believe mine came with a 178mj when I bought it in 2001 and it was rich I went down to 175 and it ran great but was still a little on the rich side and probably could have gone with 172 but I opted for the Edelbrock!

Cold air is dense and lower Alt is dense so you need more fuel to keep the optimum ratio but I'm thinking 178 is a bit much UNLESS YOU HAVE HOLES CUT IN THE AIRBOX COVER???

Have him check the plug and report back?

I'll keep an eye around and maybe I'll learn something!


He got a new needle and the clip is in the middle. He removed all the crap from the airbox and installed a new intake. I don't think he tried the 175, but I'll ask. The plug looks a grayish color. He's running at about 1000-4000 FT between 50-80 degrees. He Says the bike runs like a raped ape at WOT, but it has a dead spot when you first crack it open, and pops when you let off. Since he went to a richer pilot and it helped, I figured a even bigger pilot would help more. However I know bigger is now always better.


Go to and click on the Jetting button. They do recommend a much larger pilot jet.

If its still popping as suggested you might try the 70s slow jet. It may be a long shot but check the seal where the exhast header joins the motor. If it is leaking it will also cause a pop on deceleration. As far as I know the only cure for the slight hesitation (dead spot) when snapping the throttle open is to stop snapping it open and roll on the power gradually or buy a pumper carb. The pumper carb definately cures it. :)

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