I'm stuck...really stuck.

Bone Head

Bone Head

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I've come into a "S&S Series E" carburetor for my other bike. My dilemma is some previous owner broke the brass air/fuel mixture screw off about 3/16"-1/4" up from the carb body. And it has sat for several years at least in that condition. Rest of it is in good to excellent condition.
To the point, I've had it soaking for several days in an ATF/acetone/kerosene mix and it is still stuck. Refuses to budge in either direction. I'll note at this point that the screw tip poking through can not be felt by my finger, or dragging a screwdriver tip across the hole, so the carb body is still usable I hope. Any tips about breaking down the apparent fowling locking the threads in?
Thanks.
 
Besides the acetone/ATF solution, I've had good results using both Kroil and Nuts Off penetrating oils. Other than using penetrating oils, the only other solution that I can think of is drilling it out. I have had pretty good luck using left hand drills for removing broken screws and bolts.
Best of luck
Ted

Another option may be using heat, but you risk warpage of the carb body.
 
Maybe you could try soaking the carb in boiling hot water. Aluminum expands faster than brass so
maybe worth a try. Is the end of the screw sticking out? A lot of stuff that is stuck is caused by
water so using water can be beneficial. It might aid in dissolving any corrosion that is holding in the screw.
That's the best I can come up with.
 
Hadn't tried the heat yet; may steal the wife's hair dryer and give that a shot. I think it might take some heat abuse; my engine head temps are around 300-350 degrees F. Boil it out in water? Could try that wife's asleep :D
Thanks for the ideas, I get it out I'll report back.
 
You’re likely fighting two issues if the idle mixture screw is broken off.

First is corrosion. Brass screw in aluminum housing will create that “green fuzz” over time and the aluminum itself with turn into aluminum oxide. Both will take up the screw thread clearance and lock things together. If you’re lucky, penetrating oil will gove you half a chance to get it loose.

The other is mechanical friction. What usually happens with idle mixture screws is someone gets a little “ ham fisted” and tightens it down too much. This is why I only even touch the mixture screws with thumb and index fingers and barely enough not to slip. That way, when it bottoms out, I don’t have enough of a grip to jam it.

Ham fisted tightening causes the taper point to jam in the bore, creating a super tough “stuck” (think of a MT in a drill press and what it takes to break that loose from the quill if its a good fit) and usually ends up in the tip of the screw hard jamming in the bore or (worst case) jamming the tip and them snapping it off. This often results in a total loss of the carb body. If lucky, the tip might be protruding in the venturi, and you can gently “coax” it back to where its loose. Double edged sword there though; it soft brass and you risk bending or mushrooming the tip, making it even harder to get out.

I have saved a carb with this problem before by working back the housing enough to solder a copper nut to the brass screw when nothing else worked. Not sure if it was the heat of the mechanical advantage, but it worked. That was a last ditch effort though as you run as much a chance as soldering the screw into the body as you do the nut. I don’t recommend trying that unless you’re 3 seconds from tossing the carb in the trash anyways.

I don’t envy you. I used to tell guys who did this (jammed the screw) it would be straight time and you pay if I fix it or not. Had about a 50% success rate if the tip was indeed broken off.

but if you have a situ where the end of the screw is broken off flush with the outside bore, you can often “walk back” the aluminum housing a tiny bit with a file and then cut a new slot in the screw end stub. Or perhaps enough to grab it with needle nose vice grips or similar. A bit aggressive on the carb body, but sometimes its the only option…
 
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I’ll dig one out today and do some figuring. Go slow. You’ll get it. Mine might be older B models.
 
It's had 24 plus hours of soaking now. I'm going to grab the hair dryer and one of Momma's little chap plastic cups (for ice) and give it a shock treatment. Got a new set of needle nosed vice grips, should be able to grab the nub sticking up and move it; back and forth then some PB Blaster and continue.
Wish me luck. S&S will sell me a new carb body for about $250 plus shipping. REALLY want to avoid that.
 
Problem with a hair dryer is its not very hot and it heats a large area.

Heating aluminum and brass this way results in the entire assembly gaining heat. You want something hot and concentrated that gives you a chance to heat the aluminum before much heat gets into the brass.

Another bug problem is aluminum transmits heat internally very fast and you often don’t get the expansion you need to break things loose.

The other side of that coin is you don’t want to blast an aluminum piece with concentrated heat as you run the risk of distorting it or worse yet, melting it.

Give the hair dryer a shot though, can’t hurt and it might work.
 
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