Vintage Dirt Bike Q & A

I need some serious advice please. I bought a rebuilt 78 cr125 and have never gotten it to run properly. It starts easy, idles fine, and run well at high rpms. The problem is--It won't make the transition from low rpms to midrange. It really bogs and shoots gas into the airbox.The carb is stock and I've made all adjustments I can think of.....tried different size main jets, tried a leaner slide, tried all positions with the clip on the needle. Nothing I do makes any difference with it bogging. I live in the Myrtle Beach area, so I don't think altitude is an issue. I've even split the cases to see if i had a bad seal (there wasn't) and replaced all gaskets and oil seals. The only thing I can think of is maybe the CDI or stator could be faulty. Is this a possible source of the problem? The pilot jet is stock and wouldn't think would need changing. I've got several hundred $ in this thing and still can't ride it yet! Can someone out there PLEASE HELP ME! Thanks, Doug

Just a thought, does it have reeds?
Could be the CDI or stator. I fought a KTM doing this type of thing and the pickup (stator?) finally let go 100%. Not fixed yet so I don't know if that was the original problem. See if you can borrow a couple pieces...
Oh, check the plug cap too. Maybe....?

Hi Doug,

Sounds like your float height is set incorrectly and/or a bad needle and seat. Timing could be an issue as well, the failure of electronics on these bikes will usually result in making the bike difficult to start and/or performance at high RPM's or under heavy loads.

Good luck,
Robert

Sorry to add to the list, but if gas is being kicked back into the carb, check the reeds out too...cracks, closing all the way etc.

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

Doug,

The Ì78 CR125Ìs didnÌt have reed valve cylinders unless they were Mugen kitted (or had some other type of aftermarket reed setup)÷the Ì79 CR125RZ was the first production CR125 with a reed valve cylinder.

Take care,
Robert

I just got another 83' CR125 to fix up and it was bogging/hesitating like crazy. I finally tracked it down to a bad stator coil. Luckily i have another 83' to swap parts with, but i still had to go thru trial and error to find it. I started by swapping the carb, then the reed valve, then the coil, then the cdi, and finally the stator is what did the trick. After i tested it with an ohmeter it was about 30 ohms off from the good one.

Bob