SU carb cleaning, insulators and filter box horns

[lfesenfeld]

I have a 74 260Z that I recently bought 240 carbs for, to replace the original and poor performing flat-tops. My engine and compartment are quite clean. Anyone know a way or product to remove the oxidation from the carbs and give a nice polished look to the ones I will be installing?

I believe I will need thinner insulators. Is that correct and if so why?

The filter housing I got with the 240 carbs is in poor appearance condition while my original flat-top filter box is in very good condition. I would therefor like to use that filter box. I know I would need adapter plates. Would using adapters and the other filter box (with different shaped air horns) not have a negative affect on airflow?

[Arne]

For street use, Larry, I doubt the newer airbox will affect airflow enough to notice. Track use might be different, depending on the shape of the air horns that the adapters have.

As for the insulators, I'm not sure what you will want/need. Are you going to use the 260Z manifold? Are your round-top carbs from a '72 (three screw domes w/water passages) or a '70-71 (four screw domes w/o water passages)?

Lastly, the carb domes can be polished using any normal metal polish. On the other hand, the carbs didn't come very nicely polished from the factory. They were clean, but not polished. Mine (pictured below) are typical of the original finish.

[nwcubsman]

I guess I was unaware there were different thicknesses on the insulators. The only 2 I knew of were with/without the water passages. The only reason you'd need to change them was if the studs on the intake manifold were too short to reach through or if you wanted to be sure you had water available for cold weather driving.

[lfesenfeld]

I am new to "threads". I am not sure which of two or both responses I am replying to. I will assume it is both and address both separately herein.

Arnie,

I am planning to use the 260 manifold for not wanting to remove it having done that before to replace the gasket. I have the 3-screw.

There are so many metal polishes on the market of dozens of formulations. I thought some might work much better than most.

I have gotten the carb domes to look about like yours. My float tops still need some more work. Did you replate the brass or your throttle opener, etc. or is that original? Darn nice looking engine! Are your braided hoses original? If not where did you get?

Bryan,

I have insulators on my flattops and my 240 carbs that are about 1/2" thick like Arnie's. I was told about a year ago when I was considering switching carbs that I would need new, not as thick, but was not told why. I saw pictures of the insulators that person had. They were about 1/4". I have wondered if thinner are not required because of the thickness of the 240 to 260 air filter adapters reducing the clearance between the filter and the inner fender so one can does not have the room to maneuver the filter into place.

Larry

[Arne]

I am new to "threads". I am not sure which of two or both responses I am replying to. I will assume it is both and address both separately herein.

Perfect. You're doing fine, Larry.

I am planning to use the 260 manifold for not wanting to remove it having done that before to replace the gasket. I have the 3-screw.

That will work fine. There are actually people who say the 260Z manifolds are better flowing. I don't know whether that has been proven, but it's obviously no problem to stick with them. In fact, since you are using 3-screw carbs, it should simplify the swap, as you won't have to re-work the coolant flow to the manifolds - the 3-screw carbs should have the same water passages as the flat-tops you are removing.

There are so many metal polishes on the market of dozens of formulations. I thought some might work much better than most.

I have gotten the carb domes to look about like yours. My float tops still need some more work.

Everyone has their own favorite polish. Over the years I've tried several, all gave about the same results. Maybe someone who has actually polished their SUs can chime in here?

Did you replate the brass or your throttle opener, etc. or is that original? Darn nice looking engine! Are your braided hoses original? If not where did you get?

Mine is still all original. I will end up replacing the braided hoses soon, as I don't trust 35 year old hoses. Won't throw them out, though. They'll be saved along with the Koito headlights and 1971-dated plug wires.

I have insulators on my flattops and my 240 carbs that are about 1/2" thick like Arnie's. I was told about a year ago when I was considering switching carbs that I would need new, not as thick, but was not told why. I saw pictures of the insulators that person had. They were about 1/4". I have wondered if thinner are not required because of the thickness of the 240 to 260 air filter adapters reducing the clearance between the filter and the inner fender so one can does not have the room to maneuver the filter into place.

I've seen the thin ones, but don't know what the application for them was. If the airbox fits using the thick ones, that's what I'd stay with.

[nwcubsman]

My '73 has the swap done. Actually, Steve at Z Therapy helped me with it. I have the thicker insulators and a '72 air cleaner housing and it all worked great. We used the insulators again and just sanded off the old insulator gaskets and replaced them.

Good Luck!