Vintage Dirt Bike Q & A

Hello
I have a 79 Elsinore CR250 and was getting it in running order. When it got started it ran fine until it warmed up. Then it started bogging and wouldn't seem to wind up at all. When I got back my left leg was covered with alight coat of oil, black and dark. Looking at the engine near the exhaust it is coated with black oil like it is leaking from there, is this a seal in the bottom end or is the mix to rich (with oil)? If it is a seal which one or ones is it? Also can you rebuild the rear shock on these bikes? And if you can where do I get the kit from to do it?
Thanks in advance for your responses

I have learnt the hard way that if you want bikes of this age to run really reliably you need do a complete rebuild and eliminate some of the problems of age and wear and tear "up front". I spent many months chasing down wierd jetting problems etc. only to find the crank seals were on their way out.

If your bike runs and does not spew white smoke, then the crank seal is probably OK (for the moment!) The black oil is probably coming from the exhaust port and/or the junction between the pipe and the silencer under the left-hand side panel. This is generally due to not getting the bike hot enough and/or the jetting is rich.

First off seal the pipe to the cylinder with Yamabond. Messy but effective! Get a piece of rubber hose and use it to seal the silencer to pipe joint. I believe there should be a stock part for this purpose but maybe it has gone walkabout. If you are going to stick with the Keihin I encourage you to replace the needle jet/needle and the float valve if you suspect that either of these are worn and making the bike run rich. Checkt the float height is 19mm while you're at it. You might also try a slightly hotter plug say a NGK B8EV over a B9EV.

The stock shocks are not rebuildable. You can get a set off a 1980 CR250R with reservoirs, but I would suggest you spring for a set of Works Performance. You'll never complain, and they can be set up specifically for you and the bike when you buy them.

Finally if you want a manual or parts catalog on CD-ROM, email me your street address.

Good luck.

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