Problem with FMF full system

I have a 2006 WR 450. Put on a Power Bomb header with a Q-4 exhaust. I live in Michigan so the elevation is right around sea level. This is how I re- jetted the carb. 172 main, 52 pilot, jet needle 3rd. position from the top and the fuel air screw is 1.5 turns out. Every time I get off the gas it pops like crazy out the back of the exhaust. I have taken the carb off and re-jetted 6 times to try and correct and no luck. I been on the phone with FMF every night after work trying to come up with solutions. I have had 4 other FMF systems on different bikes and quads and there has never been an issue. The funny thing is the bike starts right up, and idles perfectly. When you ride it the difference is like night and day compared to the stock system. The bike pulls harder and is a lot quicker. Just back fires and pops when you back off the gas. Any one have a problem like this? Any suggestions would be greatly appreciated.

I have a 2006 WR 450. Put on a Power Bomb header with a Q-4 exhaust. I live in Michigan so the elevation is right around sea level. This is how I re- jetted the carb. 172 main, 52 pilot, jet needle 3rd. position from the top and the fuel air screw is 1.5 turns out. Every time I get off the gas it pops like crazy out the back of the exhaust. I have taken the carb off and re-jetted 6 times to try and correct and no luck. I been on the phone with FMF every night after work trying to come up with solutions. I have had 4 other FMF systems on different bikes and quads and there has never been an issue. The funny thing is the bike starts right up, and idles perfectly. When you ride it the difference is like night and day compared to the stock system. The bike pulls harder and is a lot quicker. Just back fires and pops when you back off the gas. Any one have a problem like this? Any suggestions would be greatly appreciated.

do you have the AIS installed?

have y

whoa that was weird, well have you done all of the free mods and removed the ais system?

Your pilot is too lean. Turn your fuel screw out more, if you get more than three turns out and it doesn't fix it try a bigger pilot jet.

that seems like a big pilot....but try a higher than a 52 and adjust fuel screw accordingly

could also be a partial blockage in the pilot circuit - since he's already got a 52 in there.....

Thanks for the quick responses. I removed the AIS system and did the free mods etc. Also tried different pilot jets. I know carb basics, this is why I'm so puzzled. I think I will try playing with the fuel screw some more. It's at 1.5 turns out now. I will keep backing it out to see if I can clean up the problem. Thanks again!

Air leak?

Air leak?

:rolleyes:

I thought that is what AIS was, just a controlled air leak. :thumbsup:

I've left my AIS on and boy do I get a really loud POP if I hold it open for a while, then back off quik. :rolleyes: its like the bike is angry I decided to slow down. Ka-Blamo!!!

It reminds me of the last time I went to a Champ Car race. Every time one of the drivers let off the gas for a turn, Ka-Blamo!!! it is interesting to me that you never hear that pop on TV.

Could it be as simple as an exhaust leak? Did you replace to sealing gasket in the cylinder?

I would agree, check for an air leak, first.

Second, ensure that none of the carburetor vent lines are plugged, pinched or kinked.

Bah!

These guys are taking you down the wrong road with all this air leak stuff. A really rich pilot will dump extra fuel and lead to LOUD , random popping when deccellerating -like gunfire. You'll also get rich looking plugs, and eventually hard starting not to mention all the carbon sooting.

A lean pilot will do that muffled pop pop pop nowhere near as loud as the rich backfire.

I think your pilot jet is way too rich personally.

Try a 48 and see what happens.

Look at these jet combos- Hardly anyone at sea level in NA goes above a 48. Try a more conventional jetting combo.

http://www.thumpertalk.com/forum/showthread.php?t=411240&page=10

http://www.thumpertalk.com/forum/showthread.php?t=645339

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