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Discussion Starter · #1 ·
my buddy has 04 raptor 660r he has fmf pipe slip on kand n air filter. 145 and 150 main jets. he put a high flow alumunium air box on and it is popping and cracking and backing and dies at 3/4 throttle and up. he did not changethe pilot jets. they are still stock. i think that is his problem. what size does he need to go with. the 22.5 is what the ones he has now. thats what it says on the side. is there any thing else he needs to do? i posted in the sticky anbout jetting too.
 

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I'd say the problem is that you can't run a high-flow airfilter in a high-flow airbox with a better flowing pipe and only jump one size on your mains. Main jets control fuel from 3/4 throttle to full throttle, another indication that they are most likely the problem.

If he wants to bump the pilots for smoother idle and starts go to a 25 pilot in each carb.

If that airbox is as open as I think it is, he may need to adjust the needle if it starts to studder in the midrange.
 

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Discussion Starter · #3 ·
i think it misses backfires and dies when he gets about 3/4 up. he ordered the 25 piliots and he needs to go to 150 and 155s ?
 

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Jsut make sure spark plug is cleaned up first and gapped correctly... It sounds like you need to bump up the mains.. If its a mikuni series jets bump the mains to a 155-160, needles 3rd clip. By the sound of it as soon as it hits the mains circuit a 3/4 throttle your loosing power,. 155-160 would be a big jump, but if your dieing out it means your seriously lean at the mains. plus piped raptors run better on the rich side of the a/f ratio
 

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Discussion Starter · #6 ·
he dont have a jet kit just a little washer under the neddles to bump it up.
 

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Discussion Starter · #8 ·
he ordered the mains 155 and 160 and he is going to get the pilots too
 
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