desertdatsuns.net

Two questions;

1) What oil is preferred for carbs? Marvel Mystery? ATF? Your favorite?

2) Having some vapor lock issues after the car sits for about 15-20 minutes.
Anyone have any luck with wrapping the fuel rail? Waste of time?
I thought I would try it since I had some wrap that Velcro's on. Haven't driven it yet with it on.

Here is a pic

Does it have the heat shield under the carbs? If so, I've had good luck with Jet Hot coating OR some of that fiberglass gold adhesive foil mat.

The wrap should help, and I'm assuming the tune is perfect.

I'd also replace the PCV hose and route to vacuum, since the breather doesn't really do much, but I assume that's a temporary fix.

Dale re: damper oil, I've tried all kinds including ATF, 20wt. 3 in 1 oil and Marvel Mystery Oil. The conventional wisdom has always been to use 20 weight fluid in stock carbs, on a stock engine. Of course, if you want to experiment a bit you can try fluids with different viscosities. Interestingly, Peter Ogden and I were just talking about this today at a car show we were at. I think he may try a heavier viscosity. My current favorite (for no real good reason) is 20 weight fork oil that I bought at a local motorcycle shop. I saw this written up on one of the sites some time ago so thought I'd give it a try. As you bike guys probably know, it's clear, and I'm sure it works just like any other 20 weight damping fluid.

Regarding the vapor locking, I'm not sure why you'd have that issue on your early car. While wrapping the fuel rail may help, I'm guessing there's something else going on. Bring it by when you have a chance and I'll be happy to have a look. I've never had that issue with my Z and your Z is essentially the same.

Thanks for the input Greg & Randy. I do have the heat shield under the carbs. I'm going to put original air cleaner on the car (like the look better) and clean up some of the vacuum lines. The car runs good, but not sure the carbs are tuned perfectly. Randy, I'll get up there one of these days and take you up on your offer. Thanks for the input on the oil too, I will give that a try.

Thanks,
Dale

I used ATF back in the day, but AFT was different back then. Dexron was slippery for smooth shifts. I think it originally contained oil from sperm whales. Type F produced a firmer shift so the hot rodders would use that. Todays dexron/mercon is in the type F camp.

I have a couple bottles of fork oil if you want to try it. I quit servicing my own forks when they went to twin chamber inverted forks. I don't have 20w though, I have 15W or 85-105 which says it is 5wt.

I got a chuckle at the V-twin specific fork oil.

Insulation slows the transfer of heat but in the end everything on the planet strives for stasis. I've always been curious about vapor lock but it's never been a problem in my own Z. Since the carbs are working off a fuel bowl, not directly off the fuel lines (they via the pump just fill the fuel bowl), I would concentrate on the fuel bowls.

Goldie doesn't generally exhibit vapor lock because of the fuel rail design and the fuel "prime" (not really a prime) that the ECU does at each ignition ON. My fuel pump gets run for 4 seconds before start. The injectors are angled to the vertical with the fuel rail above so any fuel that vaporizes will rise up into the rail and then be pushed back to the fuel tank by the initial fuel pump operation.

The radiant barrier type "insulation" that Hitman suggests is pretty effective at minimizing that type of heat (radiant) which the bare exhaust is good at emitting. That's only one type of heat energy, but it's a good start. I'd try to keep heat away from the fuel bowls before I started to look at the fuel rail. If the bowls are full of liquid fuel, who cares if the rails have a little vapor in them. It'll just be spit into the bowls which always have air in the top anyway.

Another problem with heat could be fuel density. Just like air, fuel gets less dense with heat. The problem may not be lack of fuel, but less dense fuel mixing with less dense intake air making the fuel mixture swing very lean. L series engines really do not like lean conditions...

But then I always go back to - why doesn't Randy or Stephen or Gregg or Brad have a similar issue. I know through experience that every Z is unique, but all the cars mentioned have many similarities.

Too - Bob's stock 1975 280Z has horrific vapor lock issues...

P.S. The reason I mentioned Goldie - if all else fails, would someone want to install an electric pump pump on an SU engine with a switch for the sole purpose of clearing the fuel rail of vapor before start?

I know I'm a month late to this thread, but I have a lot of experience with vapor lock on my SU-equipped F54/P79 260Z race car. The car is an endurance racer, so it runs hard for 2 hours between fuel stops and can go as long as 25+ hours in a race. I had vapor lock issues both after refueling during a race and during the race itself if the ambient temps were high. I tried everything including adding extra heat shielding between the exhaust and the carbs, extra wrapping on the fuel rail, disabling the fuel return line, adding an electric fuel pump, propping the back of the hood open for increased airflow, etc. Nothing really worked and I continued to have the same issues before I fixed the problem for good. It turns out that the heat was getting to the fuel via the rail itself. Since the fuel rail is steel and it's bolted directly to the head in 3-4 places, the heat is transferred from the head directly to the rail. Adding insulation to the rail was actually making the problem worse by holding in the heat.

I fixed it by eliminating the rail completely and running rubber hose from the fuel supply pipe on the RH frame rail to the front carb and then to the rear carb via a T fitting. I eliminated the return with this setup which also keeps the hot fuel from going back in the tank and heating the whole system up further. I immediately got rid of my on-track vapor lock and the car runs great. One thing that I had done earlier to help hot restarts was to lower the electric fuel pump as low as feasible so it wouldn't have to lift the fuel to prime the pump. It's not uncommon to run the tank dry, so having a gravity fed pump helps.

Since this is a race car, I don't really care about what the engine bay looks like. For a street car, I'd probably test this first since it's a 10 minute and $5.00 test. If it works, I'd experiment with trying to insulate the rail's mounting brackets from the head. This could be done by replacing the thick steel washers with pucks similar to the ones between the carbs and the intake. It might not be as good as eliminating the rail, but it would look stock.

Great information and seat of the pants learning.

Never thought of using the plastic isolators - Makes a ton of sense!

That's probably the reason Nissan used those on almost all of their subsequent cars... Learned something new today!

Great info Jeff, thanks for the input. I think I will give some isolators a try.

Thanks,
Dale