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still backfiring and shooting flames

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OK this is the situation,,,

2008 KLX 450

Pro circuit T4 full sustem pipe for KX450F, put on my bike so header would clear the oil filter

170 main jet

42 Pilot

Flex jet fuel screw (have adjusted till it motor peaks about 1 1/2 to 2 turns per eddie's instructions)

JD red needle 4th clip from top

Air box mod

Oring mod on fuel pump

It seems to run fine until it is has been running 5 or 10 minutes and then huge backfiring and popping when it decellerates:banghead: Need your help! Ohhh, I have also replaced the copper gasket at the header. What is my next move? I hate the jetting guessing game. Help!

Edited by mugs
the pilot jet is not a 142 but 42

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OK this is the situation,,,

2008 KLX 450

Pro circuit T4 full sustem pipe for KX450F, put on my bike so header would clear the oil filter

170 main jet

42 Pilot

Flex jet fuel screw (have adjusted till it motor peaks about 1 1/2 to 2 turns per eddie's instructions)

JD red needle 4th clip from

Air box mod

Oring mod on fuel pump

It seems to run fine until it is has been running 5 or 10 minutes and then huge backfiring and popping when it decellerates:banghead: Need your help! Ohhh, I have also replaced the copper gasket at the header. What is my next move? I hate the jetting guessing game. Help!

I run the 170 main with the KX450f ncvr needle on the 4th groove,45 pilot, air box mod with a uni filter the carb screw out 1.25 to 1.75 out. No excelerator pump mod and stock header with the KX450f muffler. It seems we have pretty close to the same set-up with the exception of the mentioned above. I do get some deceleration popping and from my understanding it's ok, but as far as flames go I will run it tonight and check it out. I think you said before were the slip-on meets the header it is loose! If that be the case see if you can get some graphite paste to put in the slip joint that way you won't suck in cold air.

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You need to block the tubes for the smog pump. I had the same fight until i plugged the line coming off the intake and the larger line ,and it cured all my back firing and the flame shooting. I had fought this for a week after I bought the bike. It will work.Mine was instantly better(cured)

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You need to block the tubes for the smog pump. I had the same fight until i plugged the line coming off the intake and the larger line ,and it cured all my back firing and the flame shooting. I had fought this for a week after I bought the bike. It will work.Mine was instantly better(cured)

Good point, My AIS is blockd off, but like I said I still have a little deceeration popping but no flames shooting out. That would be an easy fix:thumbsup:

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if don't want to guess take it to a shop that has a dyno and get it tuned. I tune all my bikes on the dyno. only way to go.. Good luck

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