FCR 39mm or 41mm?

Hi all, I am very tempted to upgrade my carb to an FCR, to increase throttle response, maybe a little power but not expecting miracles. Currently the bike has an FMF powerbomb header, Yoshi RS3 end can, 3x3 and jetting sorted. Have also taken the time to remove all the "smog reduction" crap that we have from the factory over here. Anyway I digress...

In the future I intend on doing a 440 big bore with +2mm crank, I think that makes 450? The question is if I get a 39mm carb now will this work fine with this size of BB or if the 41mm would be best? Would like to add a little something to the bike in the mean time whilst I save for the rest of the parts, the intention being : BB, MRD, cams, valves, springs, crank, MCCT, and whatever else catches my eye, ha ha.

There are big plans, but they involve big bucks, so gotta start saving my pennies. :cheers:

You will be better off with the 39mm.

If you want to go for the 41mm, you should go for bigger intake valves and cams supporting the extra fuel.

Just putting a 41mm on the bike will give less power up to almost max rpms .

yeah ... SM or dirt ... in other words , what part of the power range do you use the most ?

Hi all, I am very tempted to upgrade my carb to an FCR, to increase throttle response, maybe a little power but not expecting miracles. Currently the bike has an FMF powerbomb header, Yoshi RS3 end can, 3x3 and jetting sorted. Have also taken the time to remove all the "smog reduction" crap that we have from the factory over here. Anyway I digress...

In the future I intend on doing a 440 big bore with +2mm crank, I think that makes 450? The question is if I get a 39mm carb now will this work fine with this size of BB or if the 41mm would be best? Would like to add a little something to the bike in the mean time whilst I save for the rest of the parts, the intention being : BB, MRD, cams, valves, springs, crank, MCCT, and whatever else catches my eye, ha ha.

There are big plans, but they involve big bucks, so gotta start saving my pennies. :ride:

If you are going to go stroker , why go +2mm when +4 is available....to bring it to 470cc....

The 41Fcr is required to get the best out of a stroker engine, though a 39 will still work with it..

Your parts list for your stroker project should include RHC187 Cams, +1mm valves, Stage 2 valve spring kit, Cylinder B/Bore kit, +4 Hotcams crank and 41Fcrmx and head flowing.....

Should email eddie for a quote....:cheers:

Edited by CraigoDRZ400sm
You will be better off with the 39mm.

If you want to go for the 41mm, you should go for bigger intake valves and cams supporting the extra fuel.

Just putting a 41mm on the bike will give less power up to almost max rpms .

Yeah, sorry should have mentioned either 39mm now with what I have or wait and get 41mm with everything else, have read before that the 41mm on next to standard bike will have negative effects.

yeah ... SM or dirt ... in other words , what part of the power range do you use the most ?

Probably should have mentioned, mostly road riding but I don't rev it high anyway so bottom end / mid range power is always nice.

If you are going to go stroker it why go +2mm when +4 is available....to bring it to 470cc....

The 41Fcr is required to get the best out of a stroker engine, though a 39 will still work with it..

Your parts list for your stroker project should include RHC187 Cams, +1mm valves, Stage 2 valve spring kit, Cylinder B/Bore kit, +4 Hotcams crank and 41Fcrmx and head flowing.....

Should email eddie for a quote....:cheers:

Hmmm the thought of a +4 crossed my mind, but I wondered how high maintenance the bike would become? Also I thought the 39 would be useable with a +2 and not so on a +4. I'm thinking I should be patient and buy it all together.

That's the list I dream of, been trawling alot on here checking out other peoples BB conversions. Came accross the stage 3 kit by Eddie on epicmotorsports

(tried to post URL but it wouldn't work, don't know if there are rules against this on here?)

This would be nice, just need to get some cash for end of summer so I can spend winter working on it.

Also is it easy enough to get the head flowed, I mean can any decent autotuner carry out the work or is it a more specialist job than that?

Thanks for replies everyone :ride:

the 470 motor spec is meaty in the mid range

no reliability issues .. my 470 motor has done more than 20,000 dirt miles

Also is it easy enough to get the head flowed, I mean can any decent autotuner carry out the work or is it a more specialist job than that?Thanks for replies everyone :p

Head flowing is a specialist job...Metal is removed and sometimes added (devcon to inlets) to achieve the best fuel and gas flow from your head.. ....

Accurately metered before, during and after adjustment, using a flow bench to monitor flow improvements ....

In the case of Eddie porting your head, he knows what works and what doesn't, giving equally great results....:cheers:

He has done so many he could probably port a head in his sleep....:ride:

the 470 motor spec is meaty in the mid range

no reliability issues .. my 470 motor has done more than 20,000 dirt miles

:p Thats reason enough for me to reconsider for sure, reliability was the only reason not to 470, but with that said there is no reason not too :cheers:

Head flowing is a specialist job...Metal is removed and sometimes added (devcon to inlets) to achieve the best fuel and gas flow from your head.. ....

Accurately metered before, during and after adjustment, using a flow bench to monitor flow improvements ....

In the case of Eddie porting your head, he knows what works and what doesn't, giving equally great results....:ride:

He has done so many he could probably port a head in his sleep....:bonk:

I thought this would be recommended, does he do an exchange basis? as in rework another head and I can send mine after getting reworked one. If not I'm sure I can start work on the bike and send mine.

:jawdrop:I thought this would be recommended, does he do an exchange basis? as in rework another head and I can send mine after getting reworked one. If not I'm sure I can start work on the bike and send mine.

Best off sending Eddie an email to discuss specifics...He is an easy man to talk to...:cheers:

Email...SSpeedWorks@gmail.com Phone...303-485-1858

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