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Sync Adjustment Screw Holes

cowboyup3371

cowboyup3371

Forum Guru
Past Site Supporter
Does anyone know what the thread pitch is for the sync adjustment screw holes on the 550 carbs? I know it's a M5 set screw but the pitch looks finer than a .80mm.

I have had problems getting Charmayne's 550L carbs to sync starting with a stuck nut on the adjustment screw for the same carb a few weeks ago. After replacing it and redipping the carbs for other reasons, I found the hole is stripped out completely. I'm hoping I can helicoil it but if not I'll be looking for another carb body.
 
Thanks, actually did a quick search online, why don't I ever do that first, and found its a .5mm thread (Steve confirmed this too). Unfortunately there isn't a helicoil for that size so I'm off to find a set screw in the coarse thread to fix
 
Not sure what the pitch is but I'm pretty sure you wont be finding a heli-coil that will match. It's a very fine pitch for a reason. You need small adjustment increments and the ability to keep it in place. Don't think you're going to fix it with some bandage fix. Your best bet is to replace either the aluminum lever that's stripped or the entire carburetor body.

Which carb is bad? If it's the number 2 carb then there's a roll pin that can be pressed out to remove the lever. The other two are part of the shaft assembly.
 
Number 2 carb is the one that can have the lever replace by simply pressing out the roll pin. I may have one for you if you need it. If you end up picking up an entire body, then make sure it's from a 550. The main air jet needs to be 1.6 and only the 550's used that size main air jet.
 
A coarse M6 tap drill is 5 mm. I happen to have that memorized. So a fine thread M6 tap drill is slightly larger than 5 mm.

Edit: I did some Googling. M6x0.75 tap drill is 5.2 mm. Taps seem pretty cheap. McMaster has a few length options for socket head set screws in steel, and "low strength" nuts, not too expensive. Disappointingly limited material options though.
 
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