vapor lock

allHIvw · Posted: Mon Jun 15, 2015 12:14 pm Post subject: vapor lock

hey got my first project 68 so kinda new to the scene, the bug runs good the only problem is after driving a bit at stops i get vapor lock being my fuel filter is in the rear….should i just move it to the front or go with electric? thanks

Randy in Maine · Posted: Mon Jun 15, 2015 12:19 pm Post subject:

How close (at the closest point) is the fuel line to the exhaust system (usually over by cylinder #3)?

DeathTrap · Posted: Mon Jun 15, 2015 12:27 pm Post subject:

try replacing the filter
and never diagnose it by the liquid level seen in it

Tim Donahoe · Posted: Mon Jun 15, 2015 1:02 pm Post subject:

You say the engine stops (at Stop signs, etc., I presume) when driving. Vapor lock happened to me once (the day was 114F) because my metal fuel line was touching the manifold. This also occurred after stopping and shutting off my engine for about 5 minutes (at a gas station). Upon attempting to re-start, it just wouldn't start.

You seem to be saying that this occurs while driving and while stopping (engine on). That could be caused by a lot of different maintenance issues: valves adjustment, timing, carburetor adjustment, choke adjustment, etc.

Tim
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Bob Brugge · Posted: Mon Jun 15, 2015 1:03 pm Post subject:

Mine is in the rear, it is put on with hose clamps, never have a problem with that so far.
Are you sure it is vapor lock and not icing? Have you chased down your fuel lines to be sure they haven't been re-routed somewhere they shouldn't be?

Juanito84 · Posted: Tue Jun 16, 2015 6:51 am Post subject:

My brother's Chevy truck has problems with vapor locking because the fuel line runs right next to the exhaust manifold. But if everything's set up correctly on a Bug, the fuel line should be far away from the exhaust manifold.
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sjbartnik · Posted: Tue Jun 16, 2015 7:03 am Post subject: Re: vapor lock

DeathTrap · Posted: Tue Jun 16, 2015 8:03 am Post subject:

Vapor lock smapor lock

it's a poor mans excuse to incompetence.

there is such a thing but the term and diagnosis is rarely correct.

Most always something else..

these fuel filters plug at the slightest hint of disolved slime

it's like blaming the brakes on everything except adjustment.

Bob Brugge · Posted: Tue Jun 16, 2015 9:12 am Post subject:

Chochobeef · Posted: Tue Jun 16, 2015 9:59 am Post subject:

You can try "wrapping" the metal line in rubber hose to give it some insulation. And take some wire and tie it up away from the manifold. This has worked for me as a prevention for such an occurence.

Juanito84 · Posted: Tue Jun 16, 2015 4:42 pm Post subject:

One uncle I had wrapped his fuel line with cloth. Then he had a spray bottle and would pull over and soak the cloth with water.

I don't think VW's usually have vapor locking problems but I am seriously thinking of running an electric fuel pump with a pressure regulating valve that returns excess fuel to the tank, kind of like in a fuel injection system. I'd run the return in front of the fan, or perhaps arround the venturi ring, and back to the tank. If I ever get air conditioning I'd run the fuel line along an AC line.
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If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine?

Juanito84 · Posted: Tue Jun 16, 2015 4:49 pm Post subject:

jwold · Posted: Wed Jun 17, 2015 3:00 pm Post subject:

Check to make sure your fuel line to the carb isn't plugged. I thought I had VL issues, turned out to be crud/little rock in the fuel line btw pump & carb.

MagmaJctAz · Posted: Fri Jun 19, 2015 5:21 pm Post subject:

Yes, how did you diagnose vapor lock? Was the carb empty?

I swore my 71 Chevy pickup was suffering vapor lock. It would stall when stopped, then die. It would only restart once it cooled down.

Eventually, it wouldn't start any more! Had to have it towed home. Discovered the fuel pump failed. Replaced the pump, the problem has not reoccurred in 4 - 5 years!

My point? Apparently, pumps can fail gradually. Mechanical pumps vary very little in regards to how they operate, from manufacturer to manufacturer.

What I would do in your situation is measure the pressure the pump is outputting. I forget the spec range at the moment. You can also perform a flow test, which I've never done, because it can get messy and difficult to measure.

You can also perform a vacuum test. I did this by connecting a "tee" to the suction line of the pump. Start the engine. There should be zero vacuum, because as the pump pulls fuel from the line, gravity replenishes the fuel from the tank. If you pinch the fuel line leaving the tank, you'll see vacuum increase.

You want the pump to pull a good vacuum, ~10 in/mg, when the line is pinched. This indicated a healthy pump. When the line is not pinched, (free), the vacuum should return to zero. If it does not, it will reduce flow, and can lead to vapor lock.

Another thing to check is how your fuel tank is vented. It's common for POs to plug all vent lines on the tank allowing the pump to create a vacuum within the tank.

Regards,
Mike
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NYPATER · Posted: Tue Sep 01, 2015 5:17 am Post subject: Vapor Lock

Whatever it is, it's no fun. I've sanded down the post that the pump sits on, painted the muffler, inspected the tin, moved in the lines, checked the gas tank vent and still have this empty filter, jerky running, won't start after driving problem. I read somewhere that the new gas boils at a lower temperature and a spacer can be added between the carb and Venturi. But I don't see that for a vw.
You are not alone.

Mint74bug · Posted: Tue Sep 01, 2015 7:00 am Post subject:

Kiptere · Posted: Tue Sep 01, 2015 7:03 am Post subject:

Easiest fix - get an electric fuel pump.
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Juanito84 · Posted: Tue Sep 01, 2015 1:32 pm Post subject:

Vapor lock is more of a problem on vehicles like my brother's Chevy pickup where the fuel lines run right down the frame next to the exhaust manifold. The VW has a cooler top half of the engine compartment where the fuel lines run into the pump and up to the carb so this shouldn't be a problem on an aircooled VW. The places where the fuel line might pick up heat is 1) Where it comes into through the engine tin, right above the #3 exhaust header, 2) The fuel pump, especially if your oil temps are very high, and 3) possibly the carburetor, but I doubt it. On a VW the carb is so high off the engine that any heat that reaches it isn't likely going to do a thing. Maybe with dual carbs sitting on short aluminum manifolds, yes, but a center carb, even with a heated air cleaner, no.
_________________
If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine?

TheAmazingDave · Posted: Tue Sep 01, 2015 2:09 pm Post subject:

DeathTrap · Posted: Tue Sep 01, 2015 2:58 pm Post subject:

Someone dredged up an old thread. Then hijacked it for moral support.

In my own defense and reality based vapor lock is barely if ever the culprit.
I would say inexperienced understanding of conditions make it so.

I wrap my tv rabbit ears with tin (aluminum) foil and that's about it.

The old ads of the beetle running across the sahara or death valley without issue support this.


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