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Discussion Starter · #1 ·
I'm finally swapping my motor and building my 07 Raptor 350. 11:1 Wesico piston, mild porting on the head, wrapped header, HMF muffler, high flow filter, and a cam that is slightly bigger than stock Raptor. Also adding an oil cooler with a fan.

Got a unknown brand +6 swing arm on its way. Primarily want to tune this for the dunes. I know a bigger quad would be better but, this is what I have. I'm parking the dune truck and doing minivan trips with the quad this year because of the huge increase in gas prices. My tow truck is also at the end of its life and I don't trust it to make the trip anymore.

Looking to go from the old warrior carb to a Keihin 37mm FCR from a YZ250F. I don't have a big cam, big bore, or anything crazy. Should work fine.

My searching online has brought me to start with a 35 leak jet, 42 starter jet(to eliminate bog), and around a 45 pilot with a 165 main. I'll start with a bigger pilot and main and tune it from there.

Anyone else tuned a 37mm FCR on theirs? Any other suggestions?

And the dirtbike FCR has a return cable that is supposed to help avoid the slide from sticking open. Has anyone ever seen a dual throttle cable thumb throttle? I know I can just use a single, and order a return spring for a single cable model(to see if it is stiffer).
 

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Discussion Starter · #2 ·
Got the throttle cable figured out. A stock YFZ450 one will work great(have a couple).

Ended up getting another FCR 37 from a 2007 YFZ250F, that also had the RD power bowl on it already. The gasket kits are way cheaper for this carb. I'll just sell the other one I have on eBay.
 

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Discussion Starter · #3 ·
So its running now. Runs awesome, for the most part. It is way faster responding than the old Warrior carb. My low end, pilot seems spot on. I turned the mixture screw to 2-1/4 turns out and got the best results. I have played with the pump/bleed jet a bit.

At part to near half throttle, it's super snappy and just goes to whatever throttle I give it.

At WOT and high rpm, I get a bit of a miss. Tells me the main is too rich. In-between is a bit different.

From lower rpm to WOT, I still get a stall(lean). From mid to high, it pulls hard with an occasional miss. Even with the adjustable leak jet turned up(not near all the way).

This leads me to believe I need to move the needle up, and maybe downsize the main 1 or 2 sizes.

Sound right?
 

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Discussion Starter · #4 ·
Did a 170 main to start, and a 45 pilot. AFR screw was near 2-3/4 out. Made a cheap narrow band O2 set-up. I'm 15:1 low end and 14:1 heavy to full throttle. So still need more fuel.

I'm jumping both jets up 2 sizes. 175 main/50 pilot. I'm surprised it's so thirsty for fuel.
 
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