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Old 06-20-2002, 04:51 PM
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Idle Mixture Screw - Broken Tip Removal

Idle Mixture Screw
Broken Tip Removal

Several XSives have encountered the broken idle mixture screw syndrome when overhauling carburetors. The tips break off easily in the metering hole when overtightened by overzealous "mechanics". After breaking off, the tip usually remains tightly pressed in place. Removal is essential. The problem is finding a way to apply adequate pressure on the broken tip from inside the carb throat. The "Push Pin Trick" and "Pick Trick" techniques make this possible.

Push Pin Trick
by Ken Talbot
This method uses a push pin and box wrench to push out the broken tip of the idle mixture screw.

The "Push Pin Trick" method.

Pick Trick
by Bill Kingson
This method uses a mechanic's pick and wire spark plug guage to push out and clear the broken tip of the idle mixture screw.

The "Pick Trick" method.


Broken Sewing Needle Trick
by Carlton Riggs/OldNortonRider

Below is an addendum(sorry, no pictures ) to this tech tip.
First of all, the push pin won't go into the jet hole very far without the size of the hole, stopping the push pin. And a push pin can make the size of the jet hole larger than it's suppose to be, even when the method works. Also, something with a "point", will often try to "go around" the broken-off tip.

Take an average, fair size, sewing needle; break it. (no point, now). Sewing needle doesn't bend; they break. That's what you want. For the flat, "square", sharp-edged, broken end.
Needle piece needs to be about an inch long. To "check" to see if yer needle piece is going to be about "right" >> poke it up into the throat with a pair of needle nose pliers, and see if the broken blunt end of the needle is going to be about right to try to start its way into the tiny jet hole. Don't poke the needle eye end
into the jet hole; yer gonna use the broken-sorta-flat-end.
Get the "smallest" pair of "vise-grips" ready, and a piece of wood like a small hammer handle wooden dowel, etc.

Assuming, you're feeling like the needle-piece, is correct for the job >> the needle-piece needs to be grasped "just right" with the small vice-grips >>holding the needle-piece cross-wise in the very end of the jaws of the vice-grips >> very carefully put the needle piece, held in end of vice-grips, up into the throat >> blunt end into the jet hole. (hole being aimed down) And, of course, when you're there; you can't get the needle-piece to go further, cuz the brass-broken-tip-piece is stopping it.

Get your piece of wood; you should be able to tell if everything is being held at the proper angles. (Hard to 'splain this without pictures.) OK, yer holding the vice-grips, which is holding the needle-piece. Give the vice-grips a nice, fine, rap, with the wood.
You want a hard, mean grip on the needle; or the vice-grips will slip. (which you do not want) . The broken-needle-end has to be snug against whatever is stopping it from going any further into the hole, when you rap the vice-grips.
The broken, ragged, flat tip of the needle with its sharp edges, won't try to go "around" that soft brass.
.....Should work...(?) JCarltonRiggs

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I looked in the tech tips and I didn't see anything like this in the broken idle mixture screw removal posts. It works great.

I had 2 broken mixture screws in the carbs from the E I just aquired. After spending a week and using every method and tool I had trying to get them out as I had in other carbs I finally broke down and ordered one of these.

A pin vise drill. The best $30 I've spent in a while.
It took me all of 30 minutes to get those stubborn broken ends ot of there!

I just chose a bit that fit through the oraface and began to gently drill away at it. The thing is hand operated so it doesn't just rip stuff up.

The aluminum is harder than the brass so it actually acts as a guide for the bit and keeps it digging at the brass and doesn't damage the carb body. When the bit came through inside the venturi the remainder of the tip just fell out.

Just thought you might want to add this to the tech tips.

This is where I orderd mine from but I'm sure there are other places to source them.



80 SG Ol' Okie
79 SF Traveler II (in progress)
78 E VIN # 2H7 000457 w/full touring package bought from Draketrumpet. Needs a lot of TLC
2 Fs,1 SF,1 SH.....parts.....many, many parts. Oh crap, another SG.

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