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'81 CB750K Running Rich, need advice

Badger

CB750 New member
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Bozeman, Montana
Hello all,
I bought an '81 CB750 in the spring of 2018 and worked on it all summer attempting to get it to run properly. It had everything stock, except for the exhaust which is now a 4-2 system. The original carburetors were running rich from the start, the previous owner had said it was running perfectly the year before. After munking with these carbs for a while, we figured it might cost just as much to rebuild those as it would cost to get new carbs. My father and I are not experienced with Keihin carbs, and stumbled across the twin Mikuni carb set up for the bike. We have experience tuning these carbs so we figured it would be easier to get it running properly, but it still ran rich at the smallest main jet size available. I have not started back up on the daunting task of getting that bike to run properly. It is still running rich. Changing the spark plugs seemed to lean it a little bit, but not to a ride able level. We have also checked valve lash, compression, timing, brushes, everything we could think of. The internals of the motor look very well maintained and essentially new. Has anyone else experienced a similar problem or have any insight into this issue??
 
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