Vintage Dirt Bike Q & A

Hey all. I posted a while ago about a found 76 mr250. Well I have been slowly chipping away at it. My question now is could someone tell me what the stock jets are for this carb (Keihin). ie what is the stock needle jet? The one that is in the carb now is #271006. I have no idea if this is original or what. Also ,assuming this is the original carb how do I ID it? Any help would be appreciated. I have been to pj and re-mx and bikebandit but without knowing what the carb ID is it is difficult to search for jets,etc. Thanks

I have one of these, and may put it on my MR175 at some point if I can develop porting to take advantage of it.

The stock jetting for the MR250 carb is 110 main, 140 power jet, 48 pilot, 200 air, 2.5 throttle valve, 271006 needle. My carb is stamped 073A ANG under the idle speed screw. Looking inside the carb mouth (air filter side), your carb should have a drilled/tapped opening to the left for the power air jet (this hole will probably be empty).

It's pretty common for people to change this carb out with a Mikuni, as carb and parts availability is much better than Keihin. I've had good luck with Keihins - and am a glutton for punishment - so I tend to keep the OEM carbs on my bikes.

If you decide to stick with this carb, let me know - I have a bunch more info on it.

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

Ray Thanks for the reply. So now I think I have all the correct stock jets in this carb. I dont know how I missed the stamped ID on my carb but I did. Mine is stamped 073A ANH/ Is this stock? Let me get the bike back together and I will get in touch with you. Thanks a lot! Per

Hey Ray (or anyone else) I am having trouble identifying the pilot jet? What is this and where is it located. Thanks everyone.

Yes, that stamped number seems to indicate a stock carb.

The pilot jet is a long jet that hangs down into the float bowl near the main jet, with a screwdriver slot in the top. The MR250 shop manual is available in the Manuals section and can help you locate it. The power jet is in a small round cylinder near the float bowl gasket surface; I'd check the O-ring to make sure it's OK.

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