250 Help with my Yamaha

I own a 1988 Yamaha yz 250 and recently rebuilt the engine(bottom and top end). However I am running to rich as access oil is leaking from my exhaust and the bike will start with throttle and no choke(to much fuel). However after research I have found that my carb is from a 1998 cr 250. It fits just fine in the airbox and intake so no issues there. However even adjusting the air and fuel mixture I cant get it to run leaner and want to know if I need to change my jetting and if so how and which jets do I need? Thank you
Hey welcome to DBA!
Probably not the reply you're looking for, and with a 10 year difference in carbs, and different mfgr's (Mikuni/Keihin), you might just have to do some trial and error, but;
How does the bike run?
Does it make good power?
Have you tried dropping the needle position? (raising the clip 1 notch?)

Here are some links if you haven't already explored these;
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Ok thank you I have not ridden the bike yet as it does not idle because there is not enough air in the cylinder to let it idle. However I can keep the bike with a little bit of throttle.
Welcome to DBA.
You will have to go through the carb, clean it, set the float height, and jet it. Trnsfr is right because bit will be a trial and error situation so make sure you get some jets. I would start with 2 leaner on the pilot and 1 leaner on the main. Good luck.
also that’s a 20:1 fuel ratio motor I believe so I would mix my fuel up accordingly. Verify that ratio in the manual.