desertdatsuns.net

Yesterday I stopped down to George Geringer's and took the SU's off his 73 240Z, which he claimed had not been fully gone through in over 220,000 miles. If that's true, it can only be because George drives his car a lot so fuel has not varnished parts to the point of sticking. George said soon after he bought his Z the stock flat top carbs were swapped due to the well known vapor lock issue. I was feeling inspired by Paul's excellent documentation of the work he did on Greg's 411 wiring so I thought I'd attempt to do the same on this rebuild.

While removing the carbs and linkage yesterday I noticed a few obvious things needing attention. The phenolic spacers between the carbs and the intake manifold were incorrect. They were the thin version that came with the flat tops and were not nearly 1/8" thinner than the ones used on the round tops (probably would make little if any difference in the way the car runs). Two of the throttle rods with the plastic ball ends need to be replaced as they were badly cracked and just barely hanging on. I also noticed that neither of the float bowls had gaskets on them, which is a potential fire hazzard. Additionally, the center link connecting the two carburetors had been modified/bent/welded, so there was no way to adjust the piston lift in each carb to synchronize them under acceleration.

In my next post I'll detail what I find after opening the carbs up. These carbs did come off a running/driving car, so I'm not expecting to find too much wrong with them that a full clean-up and tune won't improve dramatically.

Good luck, Randy!

Great Randy, will be interesting to follow along. You always to a nice job on Z carbs.

Dale

Well, I've got the first carb disassembled, and other than years of grime everything looks relatively intact. The first photo shows how far I typically tear carbs down when doing my rebuild (I count 66 parts). You can see in the other two photos just how gummed up the throat of the carb and the piston got after ??? years. From here everything will go into my carburetor Jacuzzi (hydro-sonic cleaner). It actually does a pretty good job of knocking most of the scud off. Hats off to Doc who gifted me the Jacuzzi (thanks Doc). It has a heater and a timer on it, making it both effective and easy to use.

I love the simplicity of SU carbs. I bought a couple of S30's out of a field for $600 back in 1983. Both were very rusty, so I parted them out and found a better car to start with. One of those cars was a '72 240Z and I kept the engine in the garage for 16 years before buying a 260Z to convert into a race car. I pulled the carbs off the L24 and went through them. Other than being grimy inside, they work perfectly to this day on my L28 engine. They are easy to tune and do great in the race car. The only thing I had to do other than SM needles was to ditch the stock fuel rail and use all rubber supply with no return line. Once I did that, the vapor lock issues were gone.

My old Austin Healy 100-4 had SU carbs. I rebuilt them when I first got the car and never had to mess with them much after that. A lot of thought went in to their design.
- Guy

Agree, they are brilliantly designed. It's a shame they've taken so much abuse over the years ("you have to tune them all the time") from those that just don't have a clue. I've found that once they're set up properly, the only thing you have to do is clean them periodically. Jeff, we've found a source in Australia for just about any needle profile you can imagine. A number of us have done quite a bit of experimenting with different needles to optimize engine performance. I'm currently running a much more aggressive needle (richer at some stations) than the SM. Happy to share what I know when you get your race car back to AZ.

Here's the "carb Jacuzzi" I mentioned.

Very cool on the needles and other SU parts! What's an ultrasonic cleaner that size run?

I am really at a crossroads on my race car. I simply don't have room for it in AZ and the owner of the garage where it is stored is getting ready to epoxy the floors, so he wants it moved. I've had the car for 12 years and many of the parts for over 30 years. It might end up being sold back in MI.

The needles I'm currently running in my Z are TF's. I was running SB's but they proved too rich for everyday driving though they did produce good results on the dyno.

Looks like Walmart has the same ultrasonic cleaner I have for $70. I'm using a Simple Green product in it diluted 4:1, but not the green stuff because we learned it will etch aluminum. The stuff to use actually says on the jug that it will not etch aluminum and it is purple colored. You can pick it up at Home Depot. Re: your race car, it would be a shame to leave it in MI or sell it. Hope you're able to find another alternative, Jeff

Thought I'd have some fun with the domes on George's carbs and surprise him so I'm polishing them. Below is the before and after.

Finished the first carb up today.