Vintage Dirt Bike Q & A

I have a 74 Elsinore CR250M, with the stock 34MM Kehein carburetor. I'm having problems with replacement parts, so I'm considering getting a new carburetor. What performance changes would I see if I downsized to a 32mm, or upgraded to a 36mm.

Would I need to make modifications to accommodate the larger/smaller carb fit the bike, or are all carbs basically the same size.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

In very general terms, a larger carb gives you more top-end at the expense of bottom-end (and vice versa)...For instance I believe DG and Fox did 38mm carbs for CR250Rs that used 36mm carbs as stock. You may be lucky and find that the difference in bore is accomodated in a common body size and you do not need to make changes to your air-box and cylinder rubber boots. I think your biggest challenge will be re-jetting and it would be very useful to find someone who has done this before and can give you a reference point. Going back to your original problem, what is it that you cannot get for the stock carb, and have you contacted Sudco? (http://www.sudco.com)

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I've purchased 3 different repair kits. Each kit contained the same needle seat, and needle valve. Honda part number 16011-357-004. the problem is, they do not fit my carb. I've even tried a repair kit for the 73 model, they are just a hair too large. The bike still has the original stock Kehein carb from when I purchased the bike new 30 years ago, (yes that's a scary statement). I'm reluctant to continue buying repair kits, when I'm 0 for 3...

Last night I took the bike to a local rider who rides a 80 250 KTM in the vintage 40+ class. He had previously built a 73/74 Ellsinore to get into the vintage movement. He thought he had the carb from that project , but the one he has is a little smaller then mine. He made a few phone calls, and thinks he's located another Kehein carb from a CR250M. Its funny to see the looks on everyone's face when pulled up with the bike on the trailer. It definitely becomes a conversation piece when everyone begins to re-live their childhood as they had a similar bike, and or wanted this bike.

I was concerned that I'd have a problem making the carb fit, if I downsized or upgraded. Since the bike is 100% stock, I'll stick with the original size so I don't have to make any changes to the rubber boots.

Thanks for the info.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

Here is one on ebay.

http://cgi.ebay.com/ebaymotors/ws/eBayI ... ename=WDVW

Rick

Thanks Rick, I'm currently the high bidder...

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

Just an update

I just received last night the carburetor purchased through e-bay, from a 73/74 Honda CR250M. Since I've been going crazy wanting to get the bike going again, I installed it, and the bike fired right up. Since it was 10:30 PM, I only let the bike run for 5 seconds. (I don't want to upset the neighbors or the wife by riding the bike in the yard that late at night.) I will remove it today, and give it a proper cleaning. Then I'll take her out to the trails, and see what happens.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

all that is really cool brough a big smile to my face happy new year keep riding!