Carb Idle Screw

[Jimmyshifts]

Hi guys,

I finally got sometime to try and tackle my problem with a idle screw head that had been worn almost smooth. I couldn't get anywhere so I resorted to drilling it out. There's still a good chunk of it in the hole and I'm afraid that I'll lose the threads on the side wall if I keep going. Does it look like I need a new carb? Its a shame since I just got them all cleaned out. has anyone used a tap and die on those holes? How can I get the replacement screw to work in that hole after I get this mess out?

Thanks,

Jim

[planedick]

You need a small easy-out to remove the remainder. Most tool stores and people like Sears have them. It sounds like you have carbs from other than a '78 because they had external screw heads that could be taken out with pliers and such.

[Jimmyshifts]

Thanks,

Someone definetly messed with these before. The other srews were missing the springs, one had a couple of o rings stuck down there, and one had the tip suck all the way in the hole.

[bikerphil]

You don't have to replace the carb body. I have a 79SF that has the same carbs as yours and had 3 broken off tips, two that I had to drill out. The holes are larger than normal, but with new mixture screws, it idles smooth at 900 RPM. The points just stick down into the carb throat more than usual. I had to shorten the springs a bit to allow this. The adjustment is much more sensitive now and takes a little longer to tune, but works very well. YMMV.

[tarzan]

I had to drill one out this summer on a friends bike.I drilled through the needle screw then tried an easy-out,but the easy-out expanded the brass out into the aluminum threads.So I had to drill it out to the minor diameter of the threads.I did this on a manual mill.A hand drill wouldnt keep it straight enough.
Once I was out as far as I could drill it,I dug the brass out of the threads with a dental pick.It was very tedious and the threads arent perfect now but it was good enough to fit the new needle.It is a good idea to get a replacement needle first so you know how much you can drill it out.Just measure the samll diameter of the thread then drill.Good luck.

[Bigleo]

I've had great success with the following method. Set the carb up in a vise. Soak the idle screw with penetrating oil. Heat the carb in the area of the idle screw threads with a propane torch till the pentrating oil really smokes. Repeat the oil and heating cycle several times. (don't get the rest of the carb body too hot, or you may damage the butterfly shaft rubber seals). Then heat the idle screw area one last time. Then while the area is still hot, hit the idle screw with an impact driver (the manual kind that you hit with a hammer), using a flat screw driver bit. You may have to grind a driver bit to fit as much of the pilot screw as possible. And if no screw driver slot remains, sharpen the screw driver bit to a blade, so as to dig into the brass of the pilot screw. One or two whacks with the hammer and the jet will loosen. Guaranteed. A sharped bit will create a slot in the remaining brass of the jet. Then use a regular screwdriver to unscrew it the rest of the way. There will be no damage to the carb threads whatsoever. Install a new jet. Don't forget to replace the small washer and rubber "o" ring at the bottom of the threaded area in the carb as well. I have done this on six carbs with seized threads, worked every time.
Leo