Vapor-Lock, Percolation, and 100LL

[Marlin F.]

After spending a good portion of the last 2 weeks by the side of the road with my hood up, I've found access to some 100LL for my 66 L79. If I am normally running 91 octane non-ethanol pump gas, what do you think a good blend would be with the av-gas? I'm hoping 75% pump and 25% av-gas will do the trick, but I defer to those considerably wiser (and more experienced) than myself. I know the general topic has gotten a lot of attention previously, but I don't recall seeing much about specific blends that might work.

Thanks in advance!

[Keith G.]

Re: Vapor-Lock, Percolation, and 100LL

I bought a barrel of 110 and mix it 50-50 for my 435 car, the 110 cost me 7.00 a gallon.

[Domenic T.]

Re: Vapor-Lock, Percolation, and 100LL

That will help (25% ) but I find 50/50 works the best for me.

DOM

[Rob M.]

Re: Vapor-Lock, Percolation, and 100LL

Marlin,

Just wondering what the driving situation/condition was that caused the issues? What was the temp that day? Have you checked the timing, etc. lately?

The one time that I had a problem with percolation/vapor lock was driving home from Tahoe on the 395 when it was 107 in the high desert - that was when I stopped for gas or lunch and had to restart the car. That was 91 octane with ethanol. It was no fun.

cheers

[Michael W.]

Re: Vapor-Lock, Percolation, and 100LL

I think I'd first find out for certain that your problem is vapour lock and not something else. 'On the side of the road' infers that the engine quit while the car was in motion. This not typical for vapour lock.

[David K.]

[Michael M.]

Re: Vapor-Lock, Percolation, and 100LL

Marlin, I use 100LL from the airport. Every six gallons of 100LL I add four ounces of Marvel Mystery Oil. I have been doing this for years without any problems.

[Marlin F.]

Re: Vapor-Lock, Percolation, and 100LL

It's been near 100* here in Kansas City for a couple of weeks, even during the evenings. The car will buck and sputter after 30 minutes of driving or will not start after a 30-minute heat soak. Cooling things down for 30 minutes or so will get me back up and going. I took it out Sunday morning when the temp was around 75* with no problems. The consistency of the variables points to a heat-related fuel problem. I wired the heat-riser valve open and have found some non-ethanol premium, which has helped, but when push comes to shove I'm still of the belief I can benefit from the stability and higher boiling point of the 100LL.

I'll let you know tomorrow!

Thanks to all...

[John D.]

Re: Vapor-Lock, Percolation, and 100LL

I used to have a lot of hot start issues on my 67 L79 due to percolation in the carb fuel bowls. Wiring the heat riser valve open helped immensely.

[Timothy B.]

Re: Vapor-Lock, Percolation, and 100LL

Marlin,

A few things I would also think about concerning the condition you describe. When the car will not restart have you removed the air cleaner lid and noticed any accelerator pump shot? Lowering the float bowls 1/16" along with making sure the air bleeds are open may help some.

The condition you describe also sounds like how a ignition coil can act when it breaks down so keep this in mind.

[Mike M.]

Re: Vapor-Lock, Percolation, and 100LL

I have a 1971 Olds 442 that I had much trouble with fuel percolation. If it was hot and you stopped for a short periord of time the car would not crank. It turned out in this case heat riser ports were letting too much heat get up under the carb. This heat was causing the fuel to percolate and the fuel would come shooting up out of a vent pipe on the top of the QJet carb. This fuel was actually shooting over into the front 2 barrells of the carb, flooding and killing the engine. In this case I bought another carb, one with an electric choke. I bought some heat riser block off plates to stop the heat from getting up under the carb (I had already tried a phenolic insulating plate, plus a buncn of other fixes.) I just drove this real stock, a/c car on a 2200 mile trip under brutal heat conditions with no further percolation problems. This will not work for everyone but perhaps it will help a few.