Obscure causes of vapor lock + how to keep engine cooler

[The Posh Mushroom]

Hello!

I have been struggling with an intermittent vapor lock issue, as well as difficult hot starts on my 1966 Beetle.

I've changed/checked pretty much all of the common causes I've seen discussed on the web.

So far I have:

-Given the bug a full tune-up: adjusted valves, changed oil, set points and timing, and tuned carburetor
-installed new engine-to-body seals, both front and rear
-installed a new, working thermostat to replace the non-functioning one
-installed new spark plug wires
-installed a new brosol fuel pump, along with a new drive rod and bakelite spacer/insulator (I made sure it dropped in freely and wiggled a bit as I know they can swell and bind the fuel pump drive rod)


However, my car still vaporlocked today after driving about an hour and a half at ~45mph, stopping for ~5min, and driving another 20min. It was about 75 degrees out and sunny, so not very hot.

I say vapor lock because the car lost pickup after shifitng into third, started to lose power, and then stalled out. It restarted and I drove into a parking lot, where I swhut it off and observed a whole lot of bubbles coming up into my fuel filter (located between the fuel pump and the carb). After about 10 minutes, I started the car again and drove about 40 more minutes home with no issues.

Could my metal fuel line be routed wrong in the engine bay? It comes through a hole in the vertical front tinwork, passes about 1/2in over the cylinder 3 tin ware, through a clip on the fan shroud, then curves around, goes over the intake manifold (again about 1/2in clearance), and into the fuel pump.

Does vapor lock always equal engine overheating?

I know installing an electric fuel pump by the fuel tank and removing the mechanical fuel pump would fix the vapor lock, but I'm afraid that the vapor locking is a symptom of my engine running hot, and if I have an electric pump, then I'll just drive until I overheat/blow the motor, because right now the vapor locking is acting like a fuse, protecting the engine from overheating.

Another thing I might try is lining the metal fuel line in the engine with DEI heat sheath or something similar to try and reduce the radiative heat vaporizing my fuel - but I'm worried that might not be enough or it could have the same effect as described above.


Any ideas of how to combat this vapor lock or help my engine run any cooler?

Engine details:

Rebuilt about 5,000 miles ago
AB- code 1300cc block
Single Port heads
Non doghouse Oil cooler/fan shroud
SVDA distributor
12V alternator
Brosol alternator style fuel pump (new)
intact thermostatic assembly with new thermostat
All tinware in place (As far as I can tell)
Stock exhaust/peashooters
Solid '66 Decklid

[raydog]

I don't see where you have replaced the fuel filter yet. There are plenty of other things to consider first before you assume vapor lock. In my experience, vapor lock has usually been an excuse to cover up some other underlying issue. Also check tank venting, tank sock, debris in the tank. Post engine photo.
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Come on, It's not rocket science. KISS

[Cusser]

Vapor lock - especially in winter - has not been a big issue for these.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[74 Thing]

Is your fuel tank vented properly? If not the fuel will not flow properly and there will be suction on the tank side.

[VW_Jimbo]

[The Posh Mushroom]

Here are photos of my engine:

Let me know if any more/different photos would be helpful, I'm happy to take them and post them here.

[The Posh Mushroom]

I actually forgot to include this on the list of work I've done, but I replaced the fuel tank vent line, so it is properly vented. The fuel filter I replaced about 8 months ago, but it looks very clear/new.

I have not checked for debris in tank, or the tank sock but when replacing flex line under the car (between the tunnel hard line and the engine hard line), I saw a smooth, uninterrupted laminar flow of gas coming out, which says to me that the line is clear and unobstructed with no debris. I will check inside the tank with a light tomorrow.

Every time this issue has caused the car to start stalling out, I have touch-tested the dipstick and it was not immediately-burn-myself hot, and I saw copious amounts of bubbles coming into the fuel filter. It also only happens when I have ran the car for over an hour, and the car will run beautifully until about 30 seconds before it stalls out. It is a sudden issue. All this combined, plus my work to vent the fuel tank and install a new filter and fuel pump, is why I think it is vapor lock.

I want to ask this again, because it's a crucial question for me and hasn't been answered yet:

How do I tell the difference between vapor lock and overheating?
They seem to have near identical symptoms (loss of power/stalling out/hesitation)

Also - If I switch to an electric fuel pump or insulate the fuel line in the engine compartment am I increasing the risk of me damaging the engine because I won't have the warning sign of vapor lock before the engine has a chance to truly overheat?

[VW_Jimbo]

Your engine bay looks good. 2 things come to mind. 1. What type of exhaust do you have? 2. Do you own an IR temp gun? 3. How is the fuel line ran coming out of the frame horn?

And if you are certain it is heat related, maybe try a few things, one at a time. Turn the mixture screw out a 1/4 of a turn. Try it a few times. This will have an immediate effect on the internal temps of the combustion chamber. The car will run cooler.

Try exchanging that steel line in the engine bay, (and the one from the frame horn if it is there) to a rubber one.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Q-Dog]

If it is vapor lock, the fuel pump or the fuel lines ahead of the pump (or maybe the entire upper part of the engine) should be pretty damn hot when the car stalls. (What is the boiling point of your fuel?) Temperature of the oil/dipstick/bottom end of the engine does not tell you how hot the upper part of the engine is.

"Vapor Lock" happens when fuel boils (vaporizes) somewhere inside the fuel system, usually inside the fuel pump or fuel lines ahead of the pump. The fuel pump can't pump vapor. So, when the car stalls you need to check if the fuel pump and lines are hot. If a hot fuel pump/fuel line is causing vapor lock, you could pour cool water on the pump/lines to cool them down and the pump should start working immediately. (I learned this little trick when I installed an electric pump inside a beetle engine compartment. Don't do that.)

If the upper part of the engine is getting hot you could have a timing problem. How are you timing this engine? Do you use a strobe? Have you verified your distributor is advancing correctly?

Heat can cause other problems too, like a coil that works when cold but fails when hot.
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Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[Slow 1200]

What exact carburettor are you running? It might not be a match to your distributor

[74 Thing]

I would make sure the vent line is clear for the fuel tank since you said you replaced it. How is it routed etc? Did you blow through it and there is no obstructions? If this happens again and your car conks out then remove the gas cap and try starting and if you hear a swoosh sound or everything is ok then it is the lack of a fuel tank vent causing suction on the gas.

Check the fuel pump too. Tee in a pressure gauge where the fuel filter is and verify the fuel pressure temporarily. https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html

You may also want to pull the fuel pump and inspect the fuel pump rod. There was a production of aftermarket rods that wore on the tip since they were not properly hardened. Also the fuel pump rod should move up and down within the fuel pump flange very smoothly. There have been reported cases of the flange being too tight and as the engine heats and expands it causes more pressure on the rod and slows the action.

[toxicavenger70]

If it was me I would temporarily install an electric fuel pump to see if it works. If it doesn't then you will know what your issue isn't.

[Michael Ambrozik]

No body has said anything about the heat risers. If they are plugged up it can cause frosting.

[viiking]

Where do you buy your fuel from? Does it occur with fuel supplied from different Brands or suppliers?

What’s your altitude where you buy fuel versus where you use the car?
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[The Posh Mushroom]

Fuel tank vent is routed properly (sideways U shape then down through hole) and clear of obstructions - I blew and sucked air through it when installing it and it was clear.

I use normal 87 Octane pump gas, usually from Arco but occasionally from other gas stations. I both use the car and buy my gas at approximately sea level. I live in CA so my gas has between 10 and 15% ethanol (don't even get me started on how stupid this is)

I just installed a new fuel pump (3 days ago), made sure the rod moved smoothly and that the spacer was not too tight.

I am running a Solex H30/31PICT and a 113 905 205K (Bosch 0 231 137 009) SVDA distributor. It is hooked to a vacuum outlet on the carb and all other vacuum ports are capped (I really doubt a carb/dizzy mismatch is my problem as I have no hesitation, flat spots, or rough running)

I bought some Design Engineering Heat Sheath, and am planning to insulate my metal fuel line in the engine bay - I will take a long drive tomorrow morning and report back here.

[74 Thing]

I would verify the fuel pressure by teeing in a gauge then if you just replaced the pump and have not verified the pressure.

[sjbartnik]

It ain't vapor lock dude
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[Slow 1200]

[Q-Dog]

I asked about how you did the timing and you didn't answer. It matters as I also don't think you have the correct carb/distributor match. Read to the end of this thread. You probably need to measure the vacuum of that carb and maybe use a different port. And use a strobe to verify the timing is advancing correctly.
https://www.thesamba.com/vw/forum/viewtopic.php?t=691755
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Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[The Posh Mushroom]