I agree, your engine can only consme/burn so much fuel, so there is a point of overkill.

 

I use them on a 686. Craycraft,Barker and Kenz all agree on using 39's over 35's. Those 3 do more raptor work than ANYBODY. Who you believe is up to you.LOL

 

Thanks for the great info & debate. This kind of discussion will help me make a decision. There is nothing like new but I like the idea of getting a used set of 35s since I could probably get close to what I paid for them when I want to upgrade to the 39's.....

Scholle, so how is the bottom end with your 39's & 686? Did you still get more than with the stock carbs?

 

How much HP will FCR 39mm add over OEM carbs on a 686?

Has any come up with a dual Mikuni set up that is cheaper?

Does anyone else think that $1K is a lot to spend for a pair of carbs?

 

Well?

 

I went straight from stock carbs to 39 fcrs and the difference was HUGE all over from bottom to top!Call Craycraft for the setup. EVERYTHING from them fits. The only thing that may not fit would be some exhausts out there.

 

So, you're saying that it is worth the $1000?

 

master pay attention to this. the fcr's do not fit most exhaust pipes, they come to close or rub against the pipe since the fcrs are way bigger than the stocks, only a few pipes clear it, barkers, sparks, and lte that i know of, im not sure if the ct does, thats why i havent considered them yet.

 

The FCRs are much better than stock on the bottom end, you don't have to wait for vacuum to build before the motor gets fuel. In the rough, FCR slides won't bounce around like the stock vacuum-controlled slides. Some folks have said that FCRs are good for an additional 5 HP on the top end but I never found it, a set of properly modified stock carbs will flat out scream on the top end. I wouldn't hesitate to run a 686 on 35mm FCRs but for a 730+, I'd recommend the 39s.

I agree with Scholle, Craycraft's FCR intake/carb/filters/boots are top quality components that fit perfectly without any frame bending or gas tank modification. To run FCRs with a Yoshi exhaust, you can spread the upper motor mount away from the frame a little and add a few washers to keep the accelerator pump from hitting the mid-pipe. Sparks X-6 and Barker's exhaust fit without any shims.

 

Edelbrock carb kit is $600. It has accel pump, and wont bounce in the rough (I hate that). They claim a 6hp increase, plus it won't tire our your thumb....And it won't be in the way of the exhaust. (I heard that CT intereferes)

I also hear that the FCRs are a pain to tweak. You end up shimming and modifing the accelerator pumps to get the right squirt.

So, what's the hype behind the FCRs?