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Old 10-16-2012, 10:53 AM   #1
gunnerbuck OP
Island Hopper
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Joined: Nov 2005
Location: N.V.I, B.C.
Oddometer: 4,351
640 FCR 37 install

After reading a few positive posts on running an FCR 37 in place of the BST I decided it was worth a try so I picked out one out of the many listed on EBAY... The one I ended up with came from a 05/06 RMZ 250 and had all the cables and the twist grip... The box showed up in the mail and upon first inspection the carb looked to be in good shape... This particular carb had the usual enricher circuit but was equipped with a hot start circuit as well...The slide looked good with not to much wear showing so I cycled the throttle cam, as the slide lifted out came a shot of rotten smelling fuel from the A.P. nozzle... I was thinking, wow this guy mailed out the carb and did not even empty out the crappy fuel, at least I know the A.P. is working... I then pulled the float bowl and noticed that there was quite a bit of rotten fuel varnish coating the inner workings so I ordered up a rebuild kit... The throttle cable also looked a bit pooched so one for an SXC is on the way...

The first thing I noticed when comparing is the bell to bell measurement on the FCR is about 15-20mm shorter than on the BST..

Also the FCR has a smaller air box end Bell

I did some measuring and found that I could make an adapter piece out of some 2 1/4" SS exhaust pipe...

Very close to the size required with a bit of work...

I ground the lip off the airbox bell end of the FCR and tested my sample adapter piece...

With some persuasion I figured it would fit so I coated the bell with 648 retaining compound...

I then heated the piece to expand it and persuaded it on with the help of a block of wood and a hammer... This proved to be a very tight fit, so much so that it will have to be cut off with a dremmel if I ever have to remove it...

I then measured the final product FCR against the BST

And see that to be perfect, I could of left a couple more MMs length on my adapter... Oh well, the slightly shorter length will make it a bit easier to install the carb when the time comes...

Next up will be to clean out the carb and install the rebuild components when they arrive....

I will also have to figure out what jetting to go with to fit my setup... I would imagine I could go with something similar to what guys are using on the FCR 39s for starters... I really don't care so much about increases in top end performance as I do about the bottom end trail power... I am hoping to get a little more front end lofting snap out of this carb to help when bouncing small logs, rocks, roots and other trail obstacles... I would like to tune this in leaving the snorkel and airbox intact therefore keeping with the water tight integrity of the original design...

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