are all round tops the same?

[clutchdust]

forgive me if this sounds like a rookie question, since i am, after all, a rookie.

my experience with the Z consists of a little work i did on a friends '72 earlier this year. well, the good news is i'm picking up a nearly identical '73. apparently, the hitachis:cross-eye have been replaced with SU's. i am slightly confused though because although they look very much like the SU's on the '72, i noticed these have 4 bolts holding the 'dome' on where the other ones had 3. at least i think the other ones had 3. am i imagining things? were there two (or more) different types of SU's? anything i need to know about these carbs?

[Bambikiller240]

There are indeed two types of Round Top SU's. The earliest ones have the 4 screw domes that you mention. They are supposed to be more desirable to racers, though I don't know the reason that they are more desirable. It could be that they do not have provision for the engine coolant to preheat them like the 3 screw one do. The 3 screw Round Top SU's are from later 240Z's, like in 1972 (prior to the Flat -top Hitachi's being used in 1973) You may be able to find more info on www.ztherapy.com. They are reputed to be the best rebuilder of SU's in the country. Good Luck!

[2ManyZs]

The main reason the 4 screw are more desirable is that they use 4 screws to mount the dome, which keeps the dome alignment in the proper postion relative to the carb body, which lessens the chance of piston binding. It just makes it less likely the dome can be installed off center enough that the piston could possibly bind in its travel.

[clutchdust]

thanks guys. sounds like either way, i'm golden! right?

[Bruce Palmer]

Hi guys,

Bruce Palmer here. I'm the voice on the phone a ZTherapy and wanted to say hello and indicate to everyone we are going to try and set aside the time to get more involved here. We have even invited Mike to come to the shop to see what we do. You might want to take a miute and read the owners bio page to get a feel for who Steve and Pam are all about.

To further highlight this discussion, Hitachi built the Datsun SU under license from SU in the UK and between you and me, we think they did a better job than SU did. Having been involved with ZTherapy since Steve and Pam bought the biz, I can also testify to the fact that ZTherapy is putting out a better product today than was available previously. That's all I'll say on that subject.......

I personally have put about 400,000 miles on SUs so have a fair country knowledge of the product so run your questions by here any time and if I don't have the answer, Steve will.

Cheers

Bruce Palmer

sales@ztherapy.com

[Zedrally]

I believe that there is also a smaller diameter SU that was used in the triple ''S' es. From memory they have a smaller suction chamber and throttle body, and can be confused with 'zed SU's.

Anyone with further info?

[Bruce Palmer]

... there are 38mm (1 1/2") round & flat top Hitachis that were found on the 1600 Roadsters, 1600sss 510 and the 1800sss 610. All very good carbs but easy to tell from the 44mm Z & 2 liter roadster variety because they only have a 2 bolt mounting flange to the manifold. There was also a setup made for the Datsun 1200.....

[Gav240z]

I was under the impression that the eariler ones were 3 screw and later ones were 4 screw?

Also ClutchDust if your carbs were replaced by the British SU's then they are a slightly different carb as Bruce stated and from what I've read from the Ztherapy website they were not as good quality.

Personally I'd love to order a set of SU's from Ztherapy but after converting to AUD$ it's not worthwhile I'm better off buying the video only and say the SM needles then trying to build my own Ztherapy set in Australia.

[Bruce Palmer]

... confused. Gavin, are you saying you have HS-6 1 3/4" SUs on a Z? Not saying it can't be done just never heard of it being done. Does the fuel line from the float bowl to the bottom of the body have a wire spring wrapped around the fuel line?

Is there a little brass tag on one of the float bowl lid screws with an AUD # stamped into it? Just curious. After we do the machine work to install the roller bearings, one of the major quality differences between the Hitachi and the SU is pretty much negated so after having been "ZTherapied" they are both killer carbs.

RE: 3 screw or 4, outside of 1 less screw and the water port on the later 3 screw carbs there isn't $.13 worth of difference between 'em.

[Bambikiller240]

Originally posted by Bruce Palmer

Hi guys,

Bruce Palmer here........................... Having been involved with ZTherapy since Steve and Pam bought the biz, I can also testify to the fact that ZTherapy is putting out a better product today than was available previously. That's all I'll say on that subject.......

Hi Bruce:

Without getting into a BASHING of the previous ZTherapy owner or his product; can you enlighten us on what changes have been made to the SU's currently being sold by your company to make them better than before?

BTW, Were you at the MSA show in 2002? If so, I may have met you on the bus tour to the Nissan Museum.

Regards, Carl

[Gav240z]

At the moment I think a picture is a 1000 words as im in a hurry and will disect what you just wrote later bruce.

Here is a shot of my engine don't know if that help much.

I had a set of British SU carbs on one of my z's I will take a photo of them to show you I don't know much about em' just they were not as good for tuning and seemed to not stay in good tune.

[Gav240z]

Not sure if these answer your question I will try take a photo of the british ones not on this car or any car at the moment for you later.