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Need help installing needle jet

Elroy750

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Hi, I bought a 1977 cb750f supersport last fall and I am working on rebuilding the carburetors. The bike has not run in 30 years. I disassembled the first carb and cleaned it and was putting it back together and I was not able to install the new needle jet. I ended up bending it. I think I am just going to reinstall the old one and not mess with them on the other three carbs. Is there a trick to getting them to seat properly?
 

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I never use the new ones. But if you are going to reuse the old ones I suggest using them on all 4. They do get a slight amount of wear and if you have 1 new and three old it can make you jetting off. Best to keep all 4 the same an eliminate some headaches. Very small changes can have drastic affects on jetting
 
The bending shows it was likely put in upside down. Convex end goes down, concave goes up. The jet holder has a cup end to meet the convex and thinking both ends are different diameter, looks that way in the pic anyway. The bigger end would not go up in the smaller hole.

Can't imagine not using them as doing so should decrease vacuum pull at the needle up high in the carb bore. The bigger hole with them gone should activate needle fuel flow or 'pullover' slightly slower. That raised step in the middle of the part also seals the top of the main air bleed mixing chamber to fully premix needle bleed air better with fuel. But if the expert says so, I buy it..........it may have more effect on a CV type than direct because of the whopping greater open area with slide fully closed. I'll have to try it sometime.

Or maybe dirtdigger is saying that he just never uses the NEW part but DOES use SOMETHING there. Myself I always use a part there.
 
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The main problem I am having now is installing the original jet. It does not not want to go back into place and I am afraid to force it and damage it like I did the new jet. I put them in with the concave end down as that matched up with the top of the main jet nozzle. Not sure why it is so difficult to fit the original back into place.
 
You have likely deformed all pieces there. Your above pic orientation is correct, top of pic is same as top of carb. You put convex to concave always, the high curve in the one matches the low in the other, the two low places do NOT go together. Bending the steel likely has bent the softer brass part too.

Look close at your pic again. The bottom of that piece is slightly bigger than the top in OD. The hole in carb body is stepped tighter at the very top so the steel piece simply drops in pretty much all the way. You double check by seeing it sticking out of bore of carb before tightening anything at all. If put in right, upside down it does not stick out and wrong. The other way it will not go all the way in. Occasionally I use a wooden dowel to lightly press the steel further in if it sticks but rarely.

Go to this......

http://www.cb750.com/threads/6649-My-son-brought-home-a-toy-for-me-to-play-with

....and post #6 and enlarge that pic. Another guy has the same problem. Look at those jet holders, only the top one looks OK and the 2nd down is the worst, caused by trying to tighten down on the upper steel piece while it is upside down. The relatively sharp edge on the concave end hooks and rolls the brass out and often both parts are then junk.
 
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Thanks for all the quick responses. Looking under a magnifier I noticed a small lip that prevented the old jet from sliding into place. This is probably from when I tried to install the new jet. I did some light filing with a small rat tail file and was able to re-install the old jet. I think from now on I will leave the original needle jets and needles unless there is some noticeable wear on them.
 
X2, the needles are cut to ten thousandths of an inch, they can make 1 but 4 completely identical? Pretty d-mn difficult.
 
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