Vintage Dirt Bike Q & A

I have a 76 CR250M with a stock Keihin carb, and just put in some NOS air screws tonight and need to know what some starting points are. Somehow I had lost the smaller idle mixture screw for the Right side of the carb, and had been running it with one of a slightly different size I had pulled from a carb I had around from a 84 CR250R, until I could get the right screw. I replaced both this screw, and the larger Left side idle speed screw, but have no idea where to start the smaller screw at. My manual calls for 2 turns out as a starting point for the larger Left side screw, but doesn't talk to the smaller Right side idle mixture screw. The Keihin website isn't much help either. It simply says



One other question on this. Both screws originally came with springs to hold the screws in place when adjusted. The NOS replacement idle speed screw was in a Honda parts bag, with the proper part number Honda tag inside it, but didn't have a spring. It had a fine nut that threaded on the idle screw, presumeably as a lock nut to keep the screw in place. I had never seen this before. Is this correct or did I somehow get some counterfeit parts? Has anyone used the nut, or should I just put a spring back on the screw to hold it in place. BTW, the new screws were gun metal gray, and not the brass I am used to.

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Steve Amling

1976 CR 250M
1980 Yamaha DT100G
1980 XR 200
1981 CSR650

1.5-2 turns out is the starting point for the air screw. You turn the other screw out until the bike is idling, but nearly stalling.

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

Honday clearly changed this part somewhere along the line, if you look up microfiches. However, I can't comment on if yours is correct or not, since when I went to order one at local dealer, I was told they are no longer available anywhere--obviously a wrong statement. I just bought a complete carb to salvage the air mixture screw, idle speed screw and other parts I may someday need.

Well so much for the idle speed screw with a stop nut to keep it in place. The screw worked fine, and I was finally able to get the bike to idle right. But, it fell out within 20 minutes of my first run with it in. This screw really needs the spring to keep tension on it. I put the old screw and spring back in and am back to having trouble getting it to idle. Back to the search for new screws again.

Mitchie, I didn't get the screws from a dealer, got them on e-pay. They were advertised as NOS, and came in bags with Honda tags and the correct part numbers, just no springs in the idle speed screw. I have given up on being able to get almost anything from a local dealer, other than tires. Everytime I go in with a parts list for even the most ordinary items, they search the system and tell me no luck. The parts manager at the largest local dealer said that they had a recall for parts for models over 15 years old a few years back, and had packed up everything and sent it all back to Honda for a credit. He said that there is a nationwide search program for parts for older Hondas, but that very little actually comes up as available for Elsinore specific parts.

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Steve Amling

1976 CR 250M
1980 Yamaha DT100G
1980 XR 200
1981 CSR650