backfire on decel

[Mercedes]

I got a 400ex 2006 curtis sparks full exaust. It backfire every time I let go of the gas. I bumped my jets up from stock 38 pilot/142 main to 42 pilot/155 main. This weekend is the first time i ride no airbox lid and still backfires. Any ideas????

[wykyd450R]

Turn the air/fuel screw out 1/4 turn at a time until the backfire goes away. If ya need to go out too far, go up 1 more size on the pilot jet, and start again.

[GPracer2500]

If it's not a lean pilot circuit then you probably have an air leak where the headers meet the head. Did you replace the crush gaskets when the exhaust was installed?

[REPOMAN]

i have the same exhaust and the same problem.

[Mercedes]

I'm gonna bump it up to a 45 ans see what happens then. I'll get back to you guy on that.


I did not know about the crush gaskets. No I did not replace them when I changed my exaust. Should they be changed everytime I change from stock exaust to Sparks. I change to original for winter riding here in Quebec.

[Barrymaxx]

How do I turn the fuel screw? With a short screwdriver?

Mine dosent fully backfire, just a little popping when I let off the gas.

[GPracer2500]

Originally posted by Mercedes
I'm gonna bump it up to a 45 ans see what happens then. I'll get back to you guy on that.


I did not know about the crush gaskets. No I did not replace them when I changed my exaust. Should they be changed everytime I change from stock exaust to Sparks. I change to original for winter riding here in Quebec.

They should be changed every time the headers are removed. I've reused old ones before though. You just run the risk of having a leak. The gaskets tend to stick into the head once crushed. Use a pick, screwdriver, and/or needle nose pliers to get the old ones out.

[GPracer2500]

Originally posted by Barrymaxx
How do I turn the fuel screw? With a short screwdriver?

Mine dosent fully backfire, just a little popping when I let off the gas.

Depends on the year. On 99-04 carbs it be turned with a small flat head screwdriver. 05+ carbs have a "D" shaped head on the screw (as an anti-tamper device).

A 90 degree screwdriver similar to this--

http://www.sudco.com/images/950-406.jpg

--is really the ideal tool. To find the best setting for the fuel screw the engine really needs to be running. The screw is really hard to adjust with the carb in place unless you've got a 90 degree driver.