fuel needle thread pitch?

[steamer97]

I tried but could not find reference to the fuel/air needle adjustment screw thread pitch. I have come up with a size to (to the best of my ability) but I was hoping someone else here has found out by experience for sure what the thread pitch is. My plan is to chase the threads in the carbs I work on with a bottoming tap without mistakenly threading to a different pitch. I don't want to screw up here! Although I can get the screws to work pretty good with a lot of back and forth screwdriver motion with penetrant (to get the needle adjustments to work freely) a tap would be easier and better to chase out the corrosion from rusted in needles and springs.

 

[steamer97]

oH forgot, this thread pitch I need is for the gen 1 carbs.

 

[one2dmax]

I probably have a few taps on hand and want to say it's a 6mm x .5 pitch (very fine) and super easy to strip out.

 

[dannymax]

I probably have a few taps on hand and want to say it's a 6mm x .5 pitch (very fine) and super easy to strip out.

That is correct. unk:

 

[caseyjones955]

Very delicate, handle with care, just dont ask me how I know haha.

 

[steamer97]

Thanks for the quick replies all. I had thought (by using a thread pitch gauge)It was a 6mm x .5 and I see that you all concur. So tiny of a thread that I wanted to be especially sure. I've been thinking about it knowing that there are different tolerances (grades) of fit for threads and taps. I am remembering that every time (in my youth) I have ever ran a tap down a head bolt hole I have ended up cutting away more metal. Must have been grade 6 (lower numerals are tighter tolerances). I should have used a thread chaser instead. These 6mm brass needle threads are too small to make a thread chaser out of one by cutting slots longitudinally, so I have decided a safe way to go. Will use a bore brush intended for firearms. Brass. I will just match one up with the old needle at a gun shop. Thanks again for the help...

 

[steamer97]

Oh I think I have found a "secret" since I don't think it has been mentioned on this forum. I have had success with using penetrant and a left hand wound drill bit to remove stubborn fuel needle jets. But last year I ruined one carb body by a botched drilling. And wouldn't you know it? It was the body with the extra casting on it for the choke (#2, I vaguely recall). So this year (I have a bin full of carbs) I let the PB blaster soak over night and it didn't help in removing three fuel needles this morning. I disassembled the carbs, put them upside down on the bench, and heated the needle thread area with a map gas torch. Wow! with lots of wrist action I got all three out without further incident. To me, a seldom mechanic (anymore), this was quite a breakthrough. I was and am very happy and I am confident I may be able to fix all my sets that are so corroded inside there. Oh, by the way, I have installed slide diaphragms from JBM industries on two sets of carbs now. They are less expensive than the ones that resemble stock mikuni and they install easier. work just fine and are all rubber, no fabric within them.