Just sold my fmf's and bought CPI's

[Too Many Toys]

I just sold my fmf pipes and bought some cpi in frames. I also changed my domes from 21cc to 18cc. Does anyone have information on if I should have to re-jet or not. I don't remember exactly what jets I am running. The elevation here is close to 5000 feet. Let me know

[ellison445]

FMF to CPI's , Hell yeah you have to rejet The cpi flow way more then the FMF do! You might have to bump her up a couple of sizes on the mains.

[Too Many Toys]

I kind of figured I would I just wanted to make sure. So you think a couple sizes on the main should do it?

[ellison445]

Find out what you are running now, I would then bump it up three sizes on the main and do a plug check and rejet from there.

 

I kind of figured I would I just wanted to make sure. So you think a couple sizes on the main should do it?

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[Too Many Toys]

Thanks for the help. I'll start there.

[odaen]

I wouldn't be so quick to bump your mains up with CPI's. I was running 320 mains in my 4mm ported motor with CPI's. Same motor when it was bone stock with T5's ran the same jetting. I'd heard of people with ported motors and T5's going up to like 380 main jets.

 

I believe that the FMF's and T5's jet fairly similarly, but I could be wrong. The CPI's and shearers also jet similarly, but I think are just more efficient in terms of the return wave stuffing the cylinders. Again, this is just a presumption based on nothing more than my understanding.

[Too Many Toys]

Thats what I was wondering. This is a new bike I just bought and it came with fmf's on it. It hasn't been running like I thought it would so I figured the pipes and compression might be part of the problem "it only had 21cc domes i it". In my old bike I had T5's and a Pretty crazy port job and I was running 370 main jets. It ran awesome like that. I guess I could play around with it and see but I wasnt for sure if I should just throw in the bigger jets or not.

[ellison445]

Always better to start rich and work your way down, then to start lean and work your way up

[odaen]

Yeah, I agree with starting rich. But starting rich by 3 or 4 jet sizes is no fun, so if we can get him in a better ballpark, it'll save him time and headache.

 

This bike with the CPI's, it has no porting, correct?

[Too Many Toys]

The cylinders have been drag ported by K&T. I am running V-Force reeds and FTZ 35mm Carbs if this helps at all. Let me know what you guys think. Thanks

[Too Many Toys]

Yeah, I agree with starting rich.  But starting rich by 3 or 4 jet sizes is no fun, so if we can get him in a better ballpark, it'll save him time and headache.

 

This bike with the CPI's, it has no porting, correct?

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The cylinders have been drag ported by K&T. I am running V-Force reeds and FTZ 35mm Carbs if this helps at all. Let me know what you guys think. Thanks

[sand rocket]

Call Kim and ask him. Sure he could get you pretty fuggin close.

[Ducman]

I have heard that CPI's are a more efficient pipe as well, and that you dont need to jet up from FMF's or toomies, but I would probably go up 2 sizes to be safe. Better yet, put it on a dyno with a gas analyser so you know exactly what the A/F ratio is.