should i trade my 450r carb for a curtis sparks fcr

[mad4106]

My friend finds cheap broken atvs and fixes them he bought a 400ex with a 426 big bore kit on it and it has a curtis sparks fcr carb on it, he say it doesnt run right cause the carb needs cleaning or a rebuild kit he doesnt know yet, he said he wants my 450r carb off of mine and he will give me the curtis sparks fcr carb. Should i do it or keep my 450r carb? I need suggestions?!

[KKiowaTJ]

Id rather have the sparks but thats thats me. He says it needs cleaned at least or new seals etc and you have a perfect carb. If it were me i would trade if he bought the rebuild kit and a non running card for a bolt on and go 450r set up, If it is a plug and play item for him.
Yeah the CS has a better value, But your taking a chance that a jet could be stripped and JB'ed in to play off a as needed cleaned. To each his own, But he spoke up first and wants your carb, Nothing better than to sweetin a deal if thats all it needs. Good luck either way

[jman7290]

My Cousin has a Sparks carb and it is badass!

[JOHNDOE83]

Unless the sparks carb is atleast a 40mm, it wont add any HP or performance other then throttle response compared to the 450r carb.

Youd have to ask yourself, why he would want the 450r carb over the sparks.

[ds268]

Originally posted by JOHNDOE83
Unless the sparks carb is atleast a 40mm, it wont add any HP or performance other then throttle response compared to the 450r carb.

Youd have to ask yourself, why he would want the 450r carb over the sparks.

Sorry buddy this isn't true. Size doesn't necessarily determine response and carb efficiency. The main factor is turbulance within the venturi. The fcr uses a much thinner slide and a more smooth venturi where the slide cuts the walls in comparison to the much larger diameter slide of the CR roundslide. The less turbulance, the better the response, more power and smoothness of the a/f delivery.

[ish416]

That is a Sudco FCR sold by Sparks. It is just a standard FCR, nothing special but totally worth it if you can get it tuned correctly.

Not really a big difference between the 04-05 on total power but much better throttle response and feel.

[JOHNDOE83]

Originally posted by ds268
Sorry buddy this isn't true. Size doesn't necessarily determine response and carb efficiency. The main factor is turbulance within the venturi. The fcr uses a much thinner slide and a more smooth venturi where the slide cuts the walls in comparison to the much larger diameter slide of the CR roundslide. The less turbulance, the better the response, more power and smoothness of the a/f delivery.

Thats essentially exactly what I said, the only difference you failed to mention was its not a HP number its a torque value number that slightly increases, mass air flow is what counts for real HP performance and topend RPM power.

You can only achieve that with mass airflow, the 42mm 450r carb will have better HP performance then any 38, 39 or 40mm.

The flat slide in the fcr creates a stab of airflow when the throttle is cracked open, good for low to midrange performance and throttle response but does nothing for mass airflow.

Maybe you didnt read it right?

[ds268]

You can have a smaller venturi that is more smooth that will actually flow more cfm than a larger bore venturi. If the point you're trying to make is proven, then the later trx riders would be snatching up all the dime-a-dozen older 42mm carbs instead of paying to have their FCR bored to a similar size to support max power for 3x the cost of what the older carbs can be bought for.

[CJM]

No one has taken into account one very important thing:

No matter what machine those stupid FCR carbs are on they are a pain to tune properly and every damn single bike I ever see that has one is a ***** to start when hot.

[dxcody]

^^^^^^^^^

True!

04 05 450R carb gets my vote.

[Stickman400]

My '06 R has an FCR on it and no hot start and it starts in 1 kick after riding it hard for hours on end. Idk how but it does.

[CJM]

Originally posted by Stickman400
My '06 R has an FCR on it and no hot start and it starts in 1 kick after riding it hard for hours on end. Idk how but it does.

First one I heard of man.

We jetted my friends worked 06 450r and it started great. Got hot (and yea we adjusted the valves as part of the rebuild we just did) and the damn thing didnt want to start.

[Stickman400]

I know my friend that I bought it off of messed with the decompression on the cam and made it easier to start since it was a PITA to kick after removing the battery. That may have something to do with it.

[CJM]

^ Betcha

[JOHNDOE83]

Originally posted by ds268
You can have a smaller venturi that is more smooth that will actually flow more cfm than a larger bore venturi. If the point you're trying to make is proven, then the later trx riders would be snatching up all the dime-a-dozen older 42mm carbs instead of paying to have their FCR bored to a similar size to support max power for 3x the cost of what the older carbs can be bought for.

Exactly, they are boring FCRs to be like 42mm 450r carbs.