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Vapor Lock revisited

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bigjones

bigjones

Jedi Warrior
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Still having problems, but here is a good clue:
Went shopping yesterday - very hot, shops are about 10 miles away.

Done shopping, car started up no problem. Drove around parking lot to the main drag. Waited for an opening and pulled out. Then seen an SUV barrelling down on me so I punched it. That's when it momentarily stalled but then kept going but engine cutting in and out. Turned on back-up electric fuel pump and got home no problem. Very scary and annoying.

Can I eliminate the float bowl drying up when I was shopping because it started up first try? I'm thinking of the heat under the hood because tightening up the manifold nuts didn't help the exhaust stink and I'm thinking maybe blown manifold gasket.

Could it be vapor lock in the mechanical pump when it was sitting? (I've taken this pump apart and the diaphragm is in A1 condition)

My next step is ordering up a new gasket and a later mechanical fuel pump and spacer - unless I can narrow down the possibilities.
 
Just curious, but... is the supply line from the mech pump to the carbs a steel line? Mebbe replacing it with a fabric one, or better: slitting an oversize fabric hose and using that as a thermal "blanket" would change things?

....Just thinkin' out loud....
 
Doc,

Thanks for the reply.
It's a rubber fuel line from pump to carb surrounded with that foam insulation pipe stuff from Home Depot.

(Still waiting for my tennis buddy so I can try your feet-over-the-muffler trick)

Cheers!
 
This is what I learned about vapor lock, short version. You shut the car off hot. The float bowl is full and the float/needle has the line to the carb shut off. The gas gets hot in the line and boils creating an area of gasoline vapor instead of actual gas and the more it boils, the more it expands pushing liquid gas back towards the tank. You come back and fire the car up and it runs good at first from the gas still in the bowl, but after you run for a bit, the bowl starts to fill with gas vapor instead of gas and the bowl goes dry for a bit. On some cars with the fuel pump on the engine, the pump itself loses its prime because its pulling and pushing vapor instead of real gas. Once it cools off the vapor turns back to gas and its all liquid again and it runs fine, or if you can keep it running and it gets some coo fuel from the tank it will settle down. You got to keep that gas line cool. VW guys used to have this a lot and would run their gas line to a coil of copper tubing before going to the carb and put that coil in a coffee can and dump ice in there when it was hot. The answer to all this would be a way to run higher fuel pressure. Just a little more pressure and the gas won't boil. Fuel injection running 40psi never has this problem. Clothes (aluminum)pins on the gas line and all kinds of stuff has worked. Mine seems to have gone since I put the thick spacer between the carb and intake, but I have not tried it in high temps. I have tried it in the 80s and 85 is about as hot as it gets around here. I need to make a run down to Greenville and see how it does. It will be 100 down there.
 
:lol:

Have you an objection to just bypassing the mechanical pump entirely and relying on an electric one mounted in the rear?

I went thru a similar issue with this daily driver Alfa soon after purchase. It had the 2L, mechanical SPICA injection. The pump pistons were so worn the thing would vapor lock after 45 minutes, goin' 6 or 60MPH. My solution was waaay overkill, but suffice it to say the metal lines from pump to injectors went fer a chop (replaced the 2L with a Weber DCOE equipped 1750cc). Point being: A Carter #P60504 fuel pump has supplied the engine without issue for YEARS now.
 
bigjones said:
Still
Done shopping, car started up no problem. Drove around parking lot to the main drag. Waited for an opening and pulled out. Then seen an SUV barrelling down on me so I punched it. That's when it momentarily stalled but then kept going but engine cutting in and out. Turned on back-up electric fuel pump and got home no problem. Very scary and annoying.

.
Click to expand...

Mine's doing the same thing evry once an a while. Usually after the sharp turn comming out of wal mart. I have an electric pump under the hood. Once I had to get out and suck on the line to get fuel back up to the pump. I know, I know, the pump should be in the back but the P.O wired it for under the hood and I don't want to have to cut lines or run wires. Gettiing too hot to drive the thing down here anyway.
 
Electric fuel pumps in the rear near the tank for the win guys. Instant fuel no matter what the temp.

Why do you supose everything went electric. If you like a manual just use the shell of one and dummy it up.
 
Thanks for the responses.

Kim, your theory makes more sense than mine - (BTW, I'm still in debt to you for the suggestion on how to remove oil from a clutch, ha!)

As far as the electric pump by the gas tank - like Kellysguy says, it's all metal line back there and I don't relish the idea of cutting it - with my expertise I'll probably create more problems, ha!

My TR3 has a mechanical pump and I've had no problem in 10 years. And, before I fixed the cooling system, that engine would get stinking HOT. Also the carbs have no heat shield - again, no problems. Then again, there is more room in the engine bay and a couple of louvres in the hood.

I'm guessing fabricating a heat shield for the mechanical pump would be a waste of time.

You know that 5/8" spacer on the later mechanical pumps - is that alloy or something non-conducting?

Still pondering.

Cheers!
 
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