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Old 06-06-2004, 05:47 PM   #1
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Question 2 questions for the gurus re: FCR-41 carb on a 640

Hi all,

Got a problem and a question for those more experienced than I... I just got my bike from service and they properly jetted my carb (stock exhaust FYI). Test ride at the shop went swimmingly (read awesome!). Now, the second I take it off choke it dies immediately. I really do not want to take it all the way across town, so I want to see if it something I am just overlooking... IDEAS, SUGGESTIONS?

Next, is there a way to wire the stock choke (handlebar mount) on this carb rather than fiddling for the choke nob up underneath the tank?

Thanks in advance!

Michael
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Old 06-06-2004, 06:26 PM   #2
Mack
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From what I am told, a properly jetted FCR often does not require any choke, just some twist to operate the accelerator pump. The more sophisticated fuel circuits seem to handle the mixing much better then the BST, hot or cold. I would first try turning up the idle a hair, or more, see if it keeps running. Remember the FCR has not one but two air adjustment screws. Both cover the 0 to 1/8 throttle, one IMS (IIRC) has the strongest effect at zero tapering to 1/8th, the other increases its effect as you get closer to 1/8th. (One is under the carb, the other is in the intake bell.)

As I understand it, the Mikuni choke plunger can be removed and installed in the Keihin, no first hand on this. Let us know what you find. Good Luck, Mack
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Old 06-06-2004, 07:09 PM   #3
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Mack,


Thanks for the tips. I will fiddle with it some more this evening.

Michael
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Old 06-07-2004, 10:04 PM   #4
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Problem solved - slight gap allowing air where the carb mates up to the block. All is VERY well now... Holy cow! what a difference the properly tuned carb makes!!! A really significant dose of power!!!
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Old 06-07-2004, 10:11 PM   #5
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Great to hear you got it fixed. Was the intake boot swapped out during the carb change? The BST and FCR boots look pretty similar, but close examination will reveal that they are different. A leak up stream of the carb is bad, but minor compared to a downstream leak that can possibly cause lean running, and engine damage. Now you can tell us about all those power wheelies, just do not dump all your oil in the airbox now.
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Old 06-07-2004, 10:40 PM   #6
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mack,


unfortunately, being a used bike with the carb already on I do not know if the boot was swapped or not. Basically it was just not tightened down well enough and the clamp "head" was in a position as such to be able to be jostled easily. I did not see it right off, but dick did as soon as I got it back over to him... I am still not so sure about all of the power wheelie claims I read in "whatever" gear... Right now I do know that it is exciting again to ride - acceleration wise... If I was doing it all over again, i would definitely instill this carb on this bike.

I am looking forward to seeing what an exhaust will do next!

Michael
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