su Is Walker 15566 the correct carb rebuild kit? YES!

[DannDZ]

I have an early 1971 Z with four-bolt round-top carbs. I am rebuilding both carbs. I was told by a number or sources that the Walker 15566 was the right kit. Imagine my surprise when I compared the provided float needle and seat to the original. It was about 0.25-inches shorter than the original, or at least the one that has been installed for at least 20 years! The shorter assembly would not allow the float height to be set correctly.

Is this the wrong kit or am I missing something? I did pick up some OEM braided hoses for the connecting the float bowl to the body of the carb. Can anyone confirm that the originals were in-fact braided?

Where do I go from here?

Dann

[Mark Maras]

@siteunseen Cliff is the expert on needle valves. The hoses from the float bowls to the nozzles were not braided as I recall. The hoses need to be SUPER FLEXIBLE (think al dente pasta) otherwise the hoses will bind the nozzles, usually preventing the nozzles from sliding up (returning) to the unchoked position. Ztherapy supplies very nice hoses that I believe are made of silicone.

[siteunseen]

Here's the hoses you can get from Nissan. I bought these a year or so ago. Maybe they're still available? Zcardepot.com has them also. They definitely aren't braided.

My needle valve advice from Bruce  at ztherapy.com was to stack those small washers to get the height you need. All those pics are on my laptop. I can post up what I have later today. Cliff

 

[siteunseen]

@jonathanrussell

Has some good information on the valves too. He's very helpful. 

[DannDZ]

@siteunseen @Mark Maras

Thanks for your responses. I can tell that the braided hoses I have from another source are not right. They were actually too large for the original hose clamps, although I was able to get them on with some help from a needle nose pliers. I will get some proper replacements.

I think I have moved to either getting the ZTherapy rebuilt kit or have them do it for me. That's been a bit of a dream for 20 years! (About the last time the updated the look of their website! Good information, old design.) 

Finally, while the suggestion is logically sound, there is no way that I could add enough washers to position it correctly. The difference is greater than the length of the threads on the valve.

-Dann

[Mark Maras]

 If you want to have a go at refreshing your SUs get Ztherapy's video "Just SUs" along with your rebuild kits. You'll be an SU expert.

[siteunseen]

I rembered something from a few years ago. Ztherapy set me some valves that were way short. I called Bruce and he said they most likely were Datsun Roadster valves. Overnighted them from California to Alabama. Fantastic customer service. 

[jonathanrussell]

I will share what I know that might be relevant to your problem.

1) Your car year and the fact that you have 4 screw carbs should mean that you have the float bowl lids with the short ears that the pin slides through to hold the pivoting float assembly. You should have short needle jets in both carbs that are 25.25mm long (measuring from end of threads to end of body...(not including the actual needle that moves in and out of the body). In 72, Nissan changed this so that the front carb uses a longer needle jet (27mm apx) and longer ears on the float bowl lid; the rear carb is the same as the earlier 4 screw carbs. So, it doesn't really make sense that the shorter needle jet wouldn't work on your carbs. They should both be short...front and rear. Questions that come to mind are....

- is the needle jet in your rebuild kit shorter than 25.25mm? If so then maybe it is the wrong kit?

- Could your carbs have been swapped with long ear float bowl lids? I personally don't like trying to make the long ear lids work with the short needle jets. I have never been able to add enough washers to work before running out of threads to securely hold the needle jet in place.

2) Personally, I have never been able to get the long ear lids to work reliably. On my 72, I swapped the front lid with a short ear lid from another set of carbs. My recollection is that the lids will interchange regardless of 4 screw or 3 screw. So, on my 72 I run short ear lids and short 25.25mm needle jets. The problem I have with the long ear configuration is that it places the float lower in the float bowl chamber. In my experience this causes the float to hang on the side of the float bowl as it rotates through its motion. The result is a needle jet stuck open and overflowing bowl. I also don't buy into the engine angle argument that resulted in the change to a longer ear in the front carb and thus the changed fuel level measurements described in Technical Bulletin TS73-10. I subscribe to, and many disagree, the method of setting floats where you equalize the fuel level directly at the nozzle tubes with the mixture nut turned 10 full turns down (bigger topic but if you are interested, search and you will find lots of discussion about this method).

3) Finally, I will offer that I have found it really important to make sure the shape of the metal tab that you bend in order to set the float level is relatively flat and not overly curved. The new aftermarket needle jets are thinner than the original ones. Because of this, they get hung on the tabs if the tabs are curved too much.

Whatever you do, I think it is really important to spend the time getting the float levels set right. If they are not set right, you will find you can't get the carbs adjusted at or near the 2.5 turns down of the mixture screw. If you find you need 3.5+ turns or 1 turn or the mixture screw turning doesn't elicit any effect, it is a good sign that your floats are not set right.

 

[DannDZ]

3 hours ago, Mark Maras said:

 If you want to have a go at refreshing your SUs get Ztherapy's video "Just SUs" along with your rebuild kits. You'll be an SU expert.

This is a very good option as I would like to retain the original carbs and don't need the "high gloss" of ZTherapy's re-manufactured units. (As beautiful as they are.) In addition, it it much less expensive.

[jonathanrussell]

One thing Ztherapy does that is sort of impractical for most of us to do ourselves is they replace the bushing in the carb bodies that the throttle shaft passes through. On worn carbs, the old bushing becomes a vacuum leak...making it very difficult to get consistent adjustment. So, you might want to test yours for leaks. You could raise idle to say 2500 rpms and spray starter fluid where the shafts enter the carb bodies. If idle changes you might have a leak. Not sure if you can send the bodies to ZT and have them just do the bushing work but might be worth asking.

[DannDZ]

1 hour ago, jonathanrussell said:

I will share what I know that might be relevant to your problem.

1) You should have short needle jets in both carbs that are 25.25mm long (measuring from end of threads to end of body...(not including the actual needle that moves in and out of the body).

1.1) Could your carbs have been swapped with long ear float bowl lids? I personally don't like trying to make the long ear lids work with the short needle jets. I have never been able to add enough washers to work before running out of threads to securely hold the needle jet in place.

Whatever you do, I think it is really important to spend the time getting the float levels set right. If they are not set right, you will find you can't get the carbs adjusted at or near the 2.5 turns down of the mixture screw. If you find you need 3.5+ turns or 1 turn or the mixture screw turning doesn't elicit any effect, it is a good sign that your floats are not set right.

 

I measured the length of the needle jets. The rear is 1.1" or 27.94 mm. The front is 1.0" or 25.4 mm. Given the crude old tool I'm using to measure and my "great skill ;)" is strongly suspect that they are both the same length and in the ball park of the 25.25 mm that you reference.

The replacement is 1" or 25.4 mm. That seems like the same length, but if you look at the pictures you will see that while the total length is the same, but the body vs threads are very different.

I measured the towers and they are all about .58" from the top ridge of the lid to the top of the tower. Same front and back.

I've added some pictures, including the heat shield which, based on the photos on ZTherapy site, this is the earliest form. I also show the jets. The one on the left is the original. Note the 1.7 on the barrel. You can see that even though they are the same, there is a big difference in the body vs the threads between the two.

Just for reference I also included two pictures of the tops with the float installed. Don't expect that they will be very helpful, but I include them just in case someone sees something that I am missing.

-Dann

[DannDZ]

1 hour ago, jonathanrussell said:

One thing Ztherapy does that is sort of impractical for most of us to do ourselves is they replace the bushing in the carb bodies that the throttle shaft passes through. On worn carbs, the old bushing becomes a vacuum leak

You are right, what they do beyond a rebuild kit adds a lot of value. I have a very tough decisions. My history with rebuilding carbs on motorcycles many years ago is not too glorious. So, maybe I should turn it over to the pros. It would be great to know that the carbs I install are balanced and set to go.