Vintage Dirt Bike Q & A

Does anyone know of a place to get a reed valve setup that would work on a 74 CR250 Elsinore. I'm racing this bike and looking for tricks. I'm already using a 38mm Mikuni carb.

A good pipe would be nice also.

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JimN
74 CR250, 75 CR250, 77 CR 125, two 83 CR 480s
74 TM125, 79 RM100

Jim,

Try searching this site using the keywords 'reed valve cr250' - I found a bunch of stuff. I never realized the GEM reed blocks required cylinder mods, I always thought they were straight up bolt-ons.

Someone with CR250M reed valve experience can surely give you better info, but if you simply bolt on one of these ancient reed assemblies without doing engine mods I would expect a slight gain in low end and a loss everywhere else; with the mods, probably a substantial gain in low end with about the same mids and less top end (all just guesses on my part). I personally love the response of piston-port motors, and if it were my CR250 I wanted to race I would just improve on the PP motor design without going to a reed valve. Combined with your bigger carb, widening all ports/passages and increasing compression should give you plenty more beef with a powerband similar to stock, and an electronic ignition (if yours uses points) would be an excellent addition. Jemco (http://www.jemcoexhaust.com) makes what looks like a low-end CR250M pipe.

Bear in mind that while a CR250M modified for mostly low end should work pretty well in the woods, the top end motors will probably smoke you on the track.

Sorry if this isn't what you wanted to hear, but I'd hate to see you spend big bucks on one of these rare reed assemblies and then be disappointed.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

John Greenway at Kleem Research put one of his own reed kits on my CR250 back about 2001. One of his pipes too. Really broadened out the powerband. I didn't think he's doing this anymore though. Haven't talked to him in years but his last phone number was: 909-687-8673

I didn't like the angle of the manifold so I borrowed a buddies mill and built my own design. Couldn't use the stock filter anymore but I did get a lot more top end over the Kleem manifold. Also did a fair amount of my own work on the ports. Overall I think I now have better bottom end and a few more ponies on top than stock.

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Those who can make you believe absurdities can make you commit atrocities.

Loren Davis
51y