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Other than a bored factory cqrb we only use a FCR. They can be sourced from many different 450 quads and dirt bikes. We adapt the factory throttle cable to the FCR. On a 686 build with the proper cam you can see an additional 3-5 rwhp over a CV.

Nate
Alba Racing
 

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they are smaller than a stock carb in size,yes they have an accelerator pump,but why would you go backwards or limit your potential with buying a smaller carb? Run a mikuni 45 hsr with the woods adapter and toss the stock airbox,thats good for a few HP for sure...a bigger carb allows for more mods to the set up, a 41 fcr limits the package right out of the box........by the way folks, a stock raptor 660 five valve motor like we have runs stock twin 32mm carbs I believe and their heads don't flow twice as much as ours, a good worked rhino head will run right with a dual port raptor head all day long,if done by the right headman...
 

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they are smaller than a stock carb in size,yes they have an accelerator pump,but why would you go backwards or limit your potential with buying a smaller carb? Run a mikuni 45 hsr with the woods adapter and toss the stock airbox,thats good for a few HP for sure...a bigger carb allows for more mods to the set up, a 41 fcr limits the package right out of the box........by the way folks, a stock raptor 660 five valve motor like we have runs stock twin 32mm carbs I believe and their heads don't flow twice as much as ours, a good worked rhino head will run right with a dual port raptor head all day long,if done by the right headman...
I couldn't agree more...........I tried the FCR, the hsr45 and the hsr48.

FCR's come on 450's for a reason....they are designed for smaller motors. IMO these larger motors need more carb especially if you plan on doing cam, bore or head work. I had a 780cc 660 based motor and the FCR just could not supply what it needed. I went to the 45 and eventually the hsr48 and had great results. IMO don't waste your time or money.
 

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my motor gained 3 HP on the dyno when I switched from a 45mm to a 48mm, and my head guy says it needs more,but I"m content,damn thing drinks gas like a motorhome....
YEah, I never had my motor dyno'd but there was a huge improvement when I switched from the stock carb to the HSR45. I never got my motor dyno'd because anything under 100hp depresses me...lol...
 

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I make custom intakes for the stock carb and hsr-45 and sell the hsr-45 carb as well...can make the for the FCR upon request...

You get an hsr-45 carb cheaper from someone else and I don't do tech support for them...have customers wanting to sell both hsr-45 and FCR 41 carbs...

Those carbs are very heavy compared to stock and well known for tearing the rubber adapters to the intake manifold so if you get one make sure it is well supported and use an intake that adds support not makes it worse...

Chris at Benchmark likes the FCR...customizes them for 660 based motors... They are well made carbs...so are the hsr-45...

I like the stock carb because it is cheap and easy... and with a good intake and correct jetting does do a good job...not saying you can't get more with a flat slide...

Unless you really know what you are doing I highly recommend getting a wide band a/f gauge for tuning any of the flat slide carbs...
 

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I dont think that an fcr 41 is going to make a big difference over a properly tuned and jetted stock cv 42mm carb,not enough to justify the cost...bet a 45 HSR would outperform that fcr....but remember all porting is not created equal...a killer port job can yield 5hp over an ok port job, I know, found out myself...and five hp on these junkbox motors is a big difference...
 

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Your motor is a big air pump....by porting the head and installing the cam you are trying to move more air..........why go smaller on your carb? Get an hsr45 and be done. They are easy to tune and work very well. Not to mention they are cheaper than the fcr.
 

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A flow bench and dyno have proven time and time again that a FCR 41 will gain power over a stock or even bored stock carb on a Ported larger than 660 motor. Just because the physical bore diameter is smaller does not mean it flows less. Don't want to get into a debate over this one just want to say that an FCR 41 is a proven power gain over a mikuni CV. Take it for what you want.

Nate
Alba Racing
 

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good point,never bothered having those flowed..........wonder if the pinch point or choked area of the fcr is actually larger than a stock carb, or maybe smaller for that point hence increasing a stronger signal or air speed venturi affect??..........nate, have you had the 41fcr flowed in comparison to the 45 HSR? That would be interesting to consider...
 
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