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Discussion Starter · #1 ·
Hi there!

I'm in the process of getting a new-to-me 1971 CB450 running well. I'll post a full post with pics and progress, but first I have a quick question regarding carburetor idle air/fuel mixture screws.

My right side carb is fine. Screw tightens firmly against the hardstop, then engine runs best (as of today, still have some tuning to do) with the screw 1/2 turn out.

The left side is a different story. The mixture screw doesn't seem to hit a nice hardstop, but rather it appears that it's smashing its tip into a wall. It's an icky feeling as you tighten it down fully to find the hardstop. The tip is slightly bent over because of whatever it's hitting inside there (pic attached). I even got a new mixture screw, gently tightened, and it bent over in the same way. I'm not cranking on the screw - just trying to get to the full-in position as reference. There's no feeling of "ah, that's fully in" - it's just a mushy ever-worsening feeling as the needle tip gets jammed against whatever it's hitting in there.

Has anyone experienced this? Any tips on what might be going on? I peered in the hole with a flashlight and couldn't see anything of interest. Can I see this tapered needle seating area if I pull the carbs off? Should I just spray in a bunch of carb cleaner and hope for the best? Perhaps I have a mis-manufactured carb body? Both are stamped Keihin 14H.

Thank you!
Max

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Sounds like the PO broke the tip off the original screw and left it in there. Time to source another carb body.
 
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Discussion Starter · #3 ·
Drat, that would be a bummer. Is there any access to that area from inside the carb? Perhaps I could dislodge the broken tip if that's indeed what's in there?
 

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At least on some carbs you can access the port inside the carb throat and, with a fine pick, dislodge the offending part. Have to be careful not to distort the port. It's the port nearest the engine.

High pressure air (100psi+) is also worth a try.
 
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