I was cleaning the carbs off and as I retightened the idle mixture screw, the tip broke.
Now its jammed in there.
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I ordered a new screw, but I can't get the old one out. Auto parts pokers were too thick, so I used a baby pin and pliers to try and force it out. I even used a mallet on the pliers, but not much can be done when the space above the hole is the top of the carb barrel

I just got back from a shop who says they can't do it with their pokers, so I guess I'm SOL? I'm ready to sell my bike, but I don't want to lose my $240 mikuni.
I want to try to drill it out, or oopsie-screw it out (but it's just the tip, so it would only be rotating.)


Can you guys give me any advice? Should I try other solutions to get the tip out or just try to drill?

I still have my cvk carb, but I'm waiting on a new diaphram because I ripped it while cleaning it too.

 

I'm assuming a screw extractor set like this one is too big?

https://amzn.to/2BTFyx9

 

Any way to post a pic of the broken screw? Just wondering if its still threaded into the body.

 

"Just the tip"
Anyway, could you use air or water pressure (or both) to force it out?

 

Hmmm...if you could plug off all bleed locations and set the carb upside down and let the tube that houses the mixture screw soak overnight in penetrating fluid...the application of air pressure from a compressor might do some good. There's also probably a better chemical that might work between the carb body and the brass piece that could dislodge the brass without damaging the carb body...but I'm not sure what chemical.

 

Which expands fastest thermally? Brass or the alloy body of the carb? Thermal expansion of metals link. Looks like a brass alloy may expand slightly slower. Without knowing the alloys for sure it is a question. Seems most aluminum alloys are around 12-13 where brasses run a shade lower. Knowing which was which would help.

Remove all parts and start heating the area where the needle is with a propane torch very slowly - don't want to risk too high temp and damage the body - although I don't know how much good it is with the needle stuck in it.

That used to be the way to get bearings out of cases, especially those in blind holes. put the case half in an oven and heat them up. I believe they'd drop out around 300-350 degrees. Could get heat to the area of the needle seat and get the needle tip to drop out. I don't think using an oven should be done with a carb, since there are other things that may be pressed in, but carefully fanning the area with a torch may do it.

Take away from this thread for those who may not already know - never "tighten" any needle valve beyond finger tight. No gripping and twisting with or without tools. They seat in lightly, otherwise they get damaged or stuck.

 

Hey guys, quick update.

I drilled out the screw tip and bike is working flawlessly.

I went to and called about 5 shops that day. No one would touch it. Shop guys like Steve would tell me it's a common issue and that my carb is a lost cause.
Iwasnt having that. I hit up farm and fleet and bought a bunch of drill bits and went home to work.

I used my dad's dewalt and only one quality drill bit to drill up the screw hole. The bit walked off-course, but I managed to drill between the broken tip and the carb body to get it loose. Came right out, anti-clumatically. Now with the carb body drilled some (not comepletely through, which is important!) the new mixture screw needed to be screwed inside more, so its at about half a turn out, if not, completely closed.

But I've put about 70 miles on the bike already the past few days, and bike is fine. Starts right up from cold with choke and a bit of throttle, then continues to idle until choke down, and ready to ride. Bike is great.
So glad I didnt lose my mikuni carb. My stock carb is giving me problems too.