Vintage Dirt Bike Q & A

hi hope some one can help me i had my first ride out on my 78 cr250 i starts great but it sounds rough at low revs and will not pull out of corners very well its ok when you get the revs up.
it has a new dg exhaust pipe and silencer fitted and was wondering if it needs the carb set up and id there any mods i could do to the engine to make it pull better.

Just as a matter of interest try the standard pipe on it. Years ago I tried a NOS DG pipe on one of mine but took it straight back off because it lost a lot of power compared to the Mugen pipe I was running.

At the time my bike was quick so being that its a case of why fix something which isn't broke I never got to use the pipe properly but I expect you will find you have to rejet the carb for the DG pipe.

If you have a stock pipe I would go back to that if only to remove the DG pipe from your performance equation. DG pipes are known for bumping top end at the expense of power lower down. That being said I would be initially interested in your carb and jetting. What is it, how old, when last rebuilt, jetting etc.?

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

redrocket, do dg pipes for a 80 cr250 have the bottom end problem as well? sorry for the hijack!

Honestly, don't know. I am repeating a generality that I remember from "back in the day". Given that the '80 engine is more mid-range oriented it might work real well with a pipe designed to boost top-end. The most important lesson here is to make changes in a controlled manner. My personal experience has been that you need to check that an engine is sound mechanically - particularly the crankshaft seals first. Then check that the carb is sound i.e. not worn out. Then change the jetting carefully from stock. Then play around with other variables like pipes and porting. If you don't establish a sound baseline it'll be very easy to chase your tail. I cured substantial jetting problems by getting two bottom-ends rebuilt and going to a new Mikuni carb. The other point is to be realistic about how much you will be able to detect and benefit from a new pipe, porting etc. I confess I needed to go from a stock pipe all the way to the most "torquey" pipe from Pro-Form to really tell the difference. But I am the other eternal novice.

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