Heat Soak Vapor Lock on 34-pict-3

[SGKent]

The question comes up a lot in summer.

Things that help:

Run premium gasoline or at least mid-grade.

Add a phenolic spacer and a gasket on each side to stop heat soak from the manifold. There are probably other sources. http://www.evolveeng.com/automotive_parts/carburetor_heat_isolator.html

Slice open a larger hose and wire tie it around the fuel hose or metal line where it is near heat sources.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[busdaddy]

Timely post Steve, I've tried all of that except the wrapping of the lines and the super duper base gasket, most of the action happens in the lines and the fuel pump. Premium non ethanol isn't what it used to be either, I have some of each stored in Jerry cans for mowers, etc. and that premium puffs up the can faster than the regular ethanol crap if you don't open the vent, still smells the same but the formula isn't like it used to be, much more volatile lately.

The EAA (experimental aircraft association) discovered this years ago when they went through the the exhausting process of getting certification to use auto gas in aircraft, the major issue aside from alcohol eating critical components was the low vapor pressure of auto gas, especially when subjected to higher altitudes. You have to buy thier paperwork to get the whole deal but there may be something useful in this non EAA sites links: http://www.experimentalaircraft.info/homebuilt-aircraft/aviation-fuel-mogas.php (As a member I'm not saying much more in regards to what the STC says since it's something you have to buy and thier lawyers can easily beat up my lawyers, yes I read the "agreement"). It's not an issue in modern fuel injected cars where the system maintains 30 psi+ at all times and circulates fresh gas every few seconds, but in near atmosphere systems like our carbed VW's or even worse a gravity fed aircraft system it becomes a real issue. Add some heat soak from being cooped up in a hot engine compartment when you park and visit the grocery store and that stuff boils, regardless of how expensive it was at the pump.

I'm currently in the first day of testing the bleed off mod we've been discussing the last few years, it worked fine yesterday when it was in the mid 80's here but today is cool so it's going to be a few days until I can post some real results.As it currently stands it's 2 Tees between the inlet and outlet of the fuel pump, one has a restrictor in it. So far so good, no hot start issues even after a vigorous drive and a 20+ minute sit (prime conditions for 10-15 extra seconds of cranking before), fingers crossed.

Nissan went to a return line system on thier cars in mid 1970 with a reed valve at the carb inlet leading back to the tank, any excess pressure tha built up was relieved by the valve, earlier cars that never had issues in the past are now making bubbles in the fuel filter and flooding when parked hot, even though thier owners spoil them with the finest gasolines available.
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[airschooled]

Got a link to the bleed off theory?

I'm at my wits end trying to find nose-down parking spots here in the Midwest.

I'll try the fuel line wrap tomorrow; I have a nice six hour trip planned for Tuesday and I'll report back.

Placing an ice cube on the pump and an ice cube on the bowl got me through South Dakota's wasteland of ethanol. "Now you can select 10, 20, 30, or 85 percent garbage at the pump!"

Robbie
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[Amskeptic]

[busdaddy]

[Wildthings]

I agree with Busdaddy that premium isn't as good as it was a few years ago. Even the alcohol free stuff doesn't give that good of a hot restart any more.

Here is a previous thread on this subject:

http://www.thesamba.com/vw/forum/viewtopic.php?p=6820610

[airschooled]

[busdaddy]

Here's one of the previous related threads: http://www.thesamba.com/vw/forum/viewtopic.php?t=523787

Nissan dealt with the issue on their F-10 in the late 70's by installing a small powerful fan up in the LR corner of the engine compartment to blow on the carb a while after shut down, kind of a band aid but it worked.
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[SGKent]

the early 70's Fiat 124 Spyder and Coupe, and my 82 CJ7 had a return line to the tank from the carb. There was a small orifice in the nipple that let a small amount of fuel return to the tank. Both engines used mechanical fuel pumps. That is the ultimate solution but it requires modifying the tank for the return line. That allows fuel to stay cooler and relieves excess pressure - the only caveat being that in a bus the tank is higher than the engine whereas in the other cars the tank was lower. I don't know what effect the higher tank will have.

Make sure that the tank vent system is working properly because pressure in the tank can play havoc with the carb.

Many of the 70's cars with carbs used the phenolic spacers - and some added a metal tray under the carb to act as a heat shield.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[RocketSurgeon]

I tried the bleed off method and it seemed to work for a while. Soon enough though I had to do the same old 15 second crank over and it would putter on and reek of fuel for the next minute or so. yuk

http://www.thesamba.com/vw/forum/viewtopic.php?t=618963

I got tired of the stink. I have a cut off valve wired into coil power now. I only have 4 inches or so of fuel line after the cut off before it gets to the carb.

Its been in for about 6 months now. Its been nice not having to worry about vapor lock this summer not a single issue since, at least with the carb. My engine has been running hot for a while and I'm stumped on that problem.
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69 Westy

[RocketSurgeon]

It's the white block mounted to the shroud.
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69 Westy

[busdaddy]

[RocketSurgeon]

The tee looked untouched. Didn't clog and didn't swell. You can't quite tell in the pic but I have the fuel line running up over the fresh air outlet on the shroud. Tried to get it away from the dual port end piece heat.
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69 Westy

[busdaddy]

Interesting, with a little Googlage I found this http://www.centuryfuelproducts.com/afc-111-12-volt-lockoff-multi-fuel-shut-off-valve.html , tiny and unobtrusive enough I might break down and allow it into my engine compartment, hmmmmmm......
It'd solve the potential gravity feed issue if the needle and seat malfunctioned as well.
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[RocketSurgeon]

That is the same one I purchased. So far so good.
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69 Westy

[cdennisg]

I have this same problem with my stock 1600 DP 34PICT3 equipped 70 camper. Doesn't seem to change with higher quality fuel either. I am glad to see some possible solutions. I like the electro-cutoff switch. I wonder if it could be mounted on top of the fan shroud?
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nothing

[wcfvw69]

[Wildthings]

I have a spare engine compartment door for my '73 think, so I drilled a 3" hole in it behind the license plate and have a computer fan mounted over the hole so that it will blow outside air over the intake manifold and carb aftershut down. I have a thermostatic switch which I need to figure out the best place to mount to give me the needed amount of run time. Will report back.

[busdaddy]

[busdaddy]