A couple of SU questions

[grannyknot]

I may have a solution for air slipping through the worn bushing, dug through my bag of gaskets and came up with a couple of Viton O rings that fit perfectly over the butter fly shaft and made up end covers of neoprene and used some Seal All to glue the edges of the cover so the shaft can move freely, I think it will work.

 

 

[davewormald]

I may have a solution for air slipping through the worn bushing, dug through my bag of gaskets and came up with a couple of Viton O rings that fit perfectly over the butter fly shaft and made up end covers of neoprene and used some Seal All to glue the edges of the cover so the shaft can move freely, I think it will work.
 
 

It would be interesting to see how much better it would run with just those vacuum leaks eliminated. It would be a lot of work just to find out, though.

Sent from my SM-S908W using Tapatalk

[dutchzcarguy]

11 hours ago, grannyknot said:

Far left and middle are original, right is the closest match.

(sarcasm..) I would never have guessed! 🙊

They differ a lot! But the old are history, try the new ones, just put in 2 exact the same needles..  Does anyone know if you can use the needles from a HMB46W  (boatanchors ? )  flathead carbs  in a roundhead HJG46W ?  Probably not.. ( Those carbs are so different it would surprise me if the needles are interchangable..)

6 hours ago, davewormald said:

It would be interesting to see how much better it would run with just those vacuum leaks eliminated.

Yeah it would, but if you do this with those rubber rings... don't expect it to last longer than a few hundred miles at the max..  you need to put in new brass bearings..  at least on the side were the axel comes out.. the other end you COULD place a cap on to let no air in.. i wonder why no one came on that solution.. i find it simple..just put a cap on the end and it's leak free.. 👍

[grannyknot]

^ Not rubber, Neoprene/Viton.

[Captain Obvious]

16 hours ago, grannyknot said:

Noooo, don't tell me that, one of the needles got bent removing it.

I'm pretty much positive the needles that come in the generic rebuild kits are the wrong profile. According to some of the documentation, they claim to be suitable for the 72 carbs, but I think that's incorrect as well.

The needles that are supposed to be in the 4-screw SU's are N-27's. I can see the "N" in one of your pics, but can't read the rest of it. Can you read it? Many people change over to "SM" needles, but I'm not a fan. If you want original profile needles and can't find them commercially, let me know.

As for sealing up the shafts, yes... One side is pretty simple. Just cap over the whole thing. Other side where the linkage connects is a little more complicated, but putting an O-ring in there would certainly help. How sloppy are they? Is the shaft worn through the chrome plating into the brass?

[Racer X]

On 7/3/2023 at 2:07 PM, grannyknot said:

Noooo, don't tell me that, one of the needles got bent removing it.

Far left and middle are original, right is the closest match.

Measure the diameter of each needle with a micrometer every 8 to 10 mm, along the shaft and compare. That should tell you if they are the same or different. 
 

I did just that when looking for an advantage by getting extra fuel with the SUs on my race Z. I was able to find a pair of needles that tapered more than the stock set, and gave more fuel, and ultimately more power and acceleration.

Edited July 8, 2023 by Racer X

[grannyknot]

7 hours ago, Captain Obvious said:

I'm pretty much positive the needles that come in the generic rebuild kits are the wrong profile. According to some of the documentation, they claim to be suitable for the 72 carbs, but I think that's incorrect as well.

The needles that are supposed to be in the 4-screw SU's are N-27's. I can see the "N" in one of your pics, but can't read the rest of it. Can you read it? Many people change over to "SM" needles, but I'm not a fan. If you want original profile needles and can't find them commercially, let me know.

As for sealing up the shafts, yes... One side is pretty simple. Just cap over the whole thing. Other side where the linkage connects is a little more complicated, but putting an O-ring in there would certainly help. How sloppy are they? Is the shaft worn through the chrome plating into the brass?

The original needle does say N27, new needle is N54, I can't see any brass on the shaft and I guess there's not much slop.  I've been working with the ITB's on the S54 engine and there is no wiggle room at all on those so these SU's feel pretty loose by comparison.

5 hours ago, Racer X said:

Measure the diameter of each needle with a micrometer every 8 to 10 mm, along the shaft and compare. That should tell you if they are the same or different. 
 

I did just that when looking for an advantage by getting extra fuel on the SUs on my race Z. I was able to find a pair of needles that tapered more than the stock set, and gave more fuel, and ultimately more power and acceleration.

OK, so the new needle is slightly bigger.

 

[Mark Maras]

 The mixture will be slightly leaner with the N 54s but I would think another 1/4 - 1/2 turn down on the nozzle screws would compensate for that.

[Captain Obvious]

4 hours ago, grannyknot said:

I can't see any brass on the shaft and I guess there's not much slop.  I've been working with the ITB's on the S54 engine and there is no wiggle room at all on those so these SU's feel pretty loose by comparison.

Well if you've been working with new ITB's, they probably have ball bearings and viton vacuum seals on the shafts. They probably are a lot smoother and tighter than the old SU stuff. If you aren't worn through the chrome, then I'd assume you're fine.

As for the needles, my notes say that the N-54's were the factory needle for the 72 year. Manual trans I believe. They should be OK for what you're doing. My assumption is over the years, they leaned things out a little bit for emissions. So the 72 needles are a little leaner than the previous years.

I've got a pair of brand new aftermarket "N-54s" here that are complete trash. The profile is so far off that it's not suitable for any Z. I think it was a screw-up by the company that sold the rebuild kit (or their supplier). The numbers for yours look much better than what I have here.

[dutchzcarguy]

20 hours ago, grannyknot said:

Not rubber, Neoprene/Viton.

Okay.. not rubber.. but just remember when the engine starts to act up after a few hundred miles that it could be that your neoprene is gone.. 

[grannyknot]

2 hours ago, dutchzcarguy said:

Okay.. not rubber.. but just remember when the engine starts to act up after a few hundred miles that it could be that your neoprene is gone.. 

The neoprene cover is cemented with Seal All, one of the very few adhesives that is gasoline resistant, it will be on there for many years I'm sure.

[dutchzcarguy]

21 hours ago, grannyknot said:

it will be on there for many years I'm sure.

Yes but only sealed to the axle as it has to be able to move.. it will wear out pretty fast as the axle has play. But we will see how long it takes i'm sure.. 😉