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kenward1000

jet needle/jet nozzle interference

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Reassembling a pair of 3-screw round tops for my 72 240z.  Trying to get the jet nozzles to go fully in smoothly, until they touch the mixture screw.  With the piston-jet needle installed, the jet nozzle binds with several millimeters to go.  When I manually retract the piston-jet needle, the jet nozzle smoothly slides in fully without binding.

I've rolled the needles on a flat plate and they're not bent.  

Is this an issue or am I over thinking this?

Searched the forums prior to posting, didn't find anything.

Regards

 

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Posted (edited)

The three screw round tops are supposed to have little conical shaped alignment pin nubbies on the top of the carb body that establish alignment with the suction chamber. Sometimes they are broken off as part of a carb rebuild process.

Are you alignment nubbies intact, or are they broken off?

If they are broken off, you'll need to manually align the suction chambers.

If your alignment posts are NOT broken off, then I would suggest that maybe you swapped the suction chamber covers between the two carbs. Any ideas about the probability that happened?

Edited by Captain Obvious
spell checker thinks it's smarter than me

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Cool, now I know what those things are called!  One carb is missing the nubbies, the other isn't.  I'm trying to build the best two carbs out of four, so yes when I did the piston drop test on all four domes and pistons, I decided to use the pair that were the closest, which means that one carb body doesn't have it's original dome/piston.

Are you confirming that there should be no binding between the needle and the nozzle, regardless of piston position?

 

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Yes, I am confirming that there should be no binding between the needle and the nozzle, regardless of piston position.

I'm thinking that the mixing and matching didn't do good things for you. If the carb body still has it's nubbies, then you need to run the original dome and piston. If the nubbies are busted off, then you'll have to do the alignment manually, so in theory you could mix parts together if you do it right.

And yes... Nubbies. It's in the manual.

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If you barely tighten the screws and get them moving freely by moving the domes around does it still bind? That's how I got mine to work good. The ztherapy dvd says tear the nubbies off anyway. 

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16 minutes ago, siteunseen said:

If you barely tighten the screws and get them moving freely by moving the domes around does it still bind? That's how I got mine to work good. The ztherapy dvd says tear the nubbies off anyway. 

Thanks for the re-alignment tip!  The Z Therapy DVD also advocates mix-n-match to find a pair of domes/pistons which have similar drop test measurements.  

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