02' YZ426F Carb rebuild

Hello all,

I am in the middle of rebuilding my Keihin FCR-MX 39, The original problem that led to a carb rebuild was my bike did not want to start very well or Idle after it was started. it would only run with the cold start on or the throttle opened off idle. I fixed this problem before by removing all the jets for inspection and cleaning them. usually it was the Idle jet that had debris in it.

This time all the rubber parts had started to fall apart. pilot screw o-ring gone. Accel pump diapham almost gone. ect.... I think the 10% ethanol in the pump gas is a big factor. I kept finding bits of rubber after all was dissasembled, so I dissasembled the fuel block from the main body and the was more rubber o-rings falling apart. :) Now to the question. These orings are not available for service from keihin. They require you to buy a whole main body. I was going to try a anarobic fuel resistant make-a-gasket sealer.

I was going to use a hyperdermic needle filled with the sealer to fill these very tiny o-ring grooves. Has any body run into this and have another idea?

My other options at this point are, but I want to try fix this one.

1. ebay-used carb

2. Edelbrock carb

3. New carb

4. New main body

Thanks for your input!

You can try the sealer, but don't get your hopes up. Your best bet is to buy a used '05 or later carb for a YZ450.

You might also try Sudco...they carry some of the "not available from Keihin" stuff...also, if you have any pieces big enough, you might try some place like Motion Industries (bearing and seal supply house). They may be able to match something up.

I have ran into a problem with the float bowl needle assembly o-ring almost right after i bought my 426, it has cracked and fell apart. Yamaha wanted to sell me whole assembly, with valve and all, even thought the valve part looked great. So (before i found out about Sudco) i went to a local hardware store and picked out a few of their general purpose o-rings. the only trouble i had with those is they were too thick. so i spent $4 and bought a variety of small ones and stretched one on and so far it did the trick :) not sure how long it will last but for $0.49 /pair i'm sold! who knows, they might even stand up to ethanol.

good luck!

Sudco does not offer the seal between the upper and lower body halves either, as far as I can see.

Separate O-rings are often listed for either the WR models, or for a number of the CRF Hondas.

Thanks Guys,

Sudco does have the rebuild kit that has everything except the fuel block seals. I've been told by several carb places (sudco included )that these cant be bought.:). These seals are similar in type but not shape to the float bowl seal. I will try to come up with a good fix and post picures.. Please keep any other Ideas comming. I can see this happening more as states adopt the E-10 fuel as mandatory. I have already replaced 2 sets of needle and seats in my friends race car in a year.

If you can find a suitable formed "O-ring", or just a round one of a suitable cross section, you might have some luck with cutting it and gluing it in place with a good fuel resistant sealer like Permatex #3, or something better. Still going to be a challenge, and in the end, the later carb is a significant upgrade, anyway.

Quite often, when you have trouble like this with a change of fuel, it has less to do with the new fuel component specifically than it does the condition of the seals in the carb. Over time, as the seals deteriorate, the components of the original fuel will permeate the rubber and become "part of the seal", replacing, in a practical sense, the missing or broken down elements of the rubber, or "reconditioning" them. When the fuel is significantly changed, the components living in the rubber may be replaced by others, which then dissolve the older ones from the seal, carrying physical parts of the seal out with them. This same thing happened to a lot of Diesel engine fuel systems some years ago when the Feds mandated a fuel formula change.

Still, ethanol does have a reputation for being less than carb-friendly, and much of it is well deserved.

I remember when the Feds mandated Ultra low sulfur diesel. I replaced alot of fuel drain valves on 7.3 powerstrokes for leaking and fuel line o-rings. :) good money for me.They acually went on backorder from the suppier several times.

I spoke to Zip Ty Racing the other day about having my carb gone over and they said there is a kit with the gaskets and seals available. Give them a call.

There are several kits available, but not with that gasket in it that I know of.

I'm having this same issue right now. Did anyone ever find the seals for sale or come up with a good solution?

I'm having this same issue right now. Did anyone ever find the seals for sale or come up with a good solution?

Contact JD Jetting.

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