Warm weather & vapor locks?

67bluegt · Aug 12, 2005

Besides my 67 fastback, I have a 66 Mustang convertible and what I believe to be a vapor lock problem. When the temp out side gets 75 degrees or hotter and I hit any traffic my engine will cut out briefly but will restart. The car has a 94 roller cam 5.0. w/ Holley 650cfm and electric fuel pump located at the tank. The temp gauge does climb but it does not pop the radiator cap. Still it must get pretty hot under there. I put a carb spacer on but it still does it. The fuel line is clear of the block. It shows up most when you turn a corner, then the engine dies for a second or two. Any ideas?

grego37 · Aug 12, 2005

Its the heads and exhaust you have to protect it from. There are various wraps, shields you can use.
but it sounds more like a float level
or fuel pressure problem, have you looked into that?

67bluegt · Aug 12, 2005

I wonder if it's possible that the oil pressure switch for the electric fuel pump cuts out briefly? All I have for a oil pressure gauge is the old 66 dash gauge and that looks pretty low when the engine is real hot. The switch is rated for 7lbs and I'm wondering if the oil pressure might drop below that setting, mainly corners and acceleration at low speeds. Once the rpms are up it seems to stop.

tos · Aug 12, 2005

Vapor lock would not happen by making a turn or accelerating and would not let you start right back up either so I think you can rule that out. As for you oil pressure switch- Maybe if your oil level was too low. Check your level and if its ok I would scratch that off the list too. Its sounds like a fuel level problem to me too. Check your float level and maybe do a flow check on your fuel pump. I knew a guy once who had a gas tank that was caved in on the bottom. It caused him all kinds of problems till he found that. Real far fetched in your case but worth mentioning.

67bluegt · Aug 12, 2005

Thanks, but the gas tank is brand new as is the pump. I have a fuel pressure gauge and it stays around 7 lbs. but it's under the hood with the engine so I can't tell if it drops when it happens. I did check float levels and both bowls checked out ok even after a resent stall. Weird.

tos · Aug 12, 2005

67bluegt said:
I have a fuel pressure gauge and it stays around 7 lbs..

I'm not talking pressure but flow. For instance if you have a filter and its clogged at Idle it will likely supply enough fuel to fill the bowls up untill you get out driving a little and that clogg causes enough restriction that the fuel level goes down to a minimum. Then you turn a corner and that little bit of fuel rolls to one side or you stomp on it and suck that little bit of fuel down before more can be supplied. This is classic fuel starvation in my opinion (turn-stall Stomp on it-stall) . Now if your stall comes just as you hit the accelerator in your turn maybe you need to check your accelerator pump adjustment. Does this happen no matter which way you turn?

67bluegt · Aug 12, 2005

Yeah, It happens both right or left turns, funny it only shows up when it's hot out? I did replace the filter the other day,( that was one of my suspects) but I could blow throught it without much trouble. I have not had the problem yet since temp outside has been lower today.

1966conv · Aug 12, 2005

With an electric fuel pump and 7 lbs pressure, it's not going to be a vapor lock problem. It could be a fuel pump problems though. What kind of pump do you have and where is it located. Most (not all) are pusher style pumps and must be located at a lower level that the output of the tank for gravity feed issues. It the pump is located higher or even level with the output you could starve the pump and be killing it.
Fuel pumps don't like cavitation, starvation or heat. Those are it's worst enemies.

If you have a little more info on the pump and location we can possibly eliminate this as a problem.

67bluegt · Aug 12, 2005

It's a Holley Red Pump and it is mounted lower than the fuel tank on steel straps just about 2 inches of fuel line from the feed on the tank. I could not get any closer.

grego37 · Aug 12, 2005

I cant tell from the pic.
is the pump mounted upright or is it on its side.

67bluegt · Aug 12, 2005

Pump is mounted upright.

grego37 · Aug 12, 2005

You have an adjustable fuel regulator and fuel pressure gauge in engine compartment , Right?

67bluegt · Aug 12, 2005

No, the pump is rated at only 7 lbs. max. Holley claims a regulator in not needed.

grego37 · Aug 12, 2005

you may want to slap a pressure gauge on there to see what its putting out.
It says it has an external pressure adjustment.

My carb guru talked me down from 7lbs to 6 to 6.5. He said when theres a quick slosh in the fuel bowls, (while cornering, quick stop, offramp) and the float moves, too much gas comes in too fast, causing a stumble or cut out of the engine.

Also my brother had a Holley red act weird on him, he had it exchanged for a good one.

67bluegt · Aug 12, 2005

Yeah, I will check out the pressure again. It could be the pump, it might act up when it's real hot and with fuel moving back and forth in the tank when taking a corner may change pressure.

thehueypilot · Aug 12, 2005

tos said:
Vapor lock would not happen by making a turn or accelerating and would not let you start right back up either so I think you can rule that out. As for you oil pressure switch- Maybe if your oil level was too low. Check your level and if its ok I would scratch that off the list too. Its sounds like a fuel level problem to me too. Check your float level and maybe do a flow check on your fuel pump. I knew a guy once who had a gas tank that was caved in on the bottom. It caused him all kinds of problems till he found that. Real far fetched in your case but worth mentioning.

I did have that problem on my gas tank and I thought I ran over something or someone tried to jack my car up by the fuel tank. Come to find out the gas cap vent, which is a slight dimple on the filler neck; surface was not enough to keep up with the pressure difference and was sucking in the bottom of the tank.

pabear89 · Aug 12, 2005

grego37 said:
you may want to slap a pressure gauge on there to see what its putting out.
It says it has an external pressure adjustment.

My carb guru talked me down from 7lbs to 6 to 6.5. He said when theres a quick slosh in the fuel bowls, (while cornering, quick stop, offramp) and the float moves, too much gas comes in too fast, causing a stumble or cut out of the engine.

With float levels set on the high side and pump pressure at 7+ with heat the fuel expands,
The lean into the corners causes the fuel level to change allowing the pressure to over ride the needle and flashover into the overflow,
This will also feel like a sudden bog or stall.

Just my 2cts

PB

67bluegt · Aug 13, 2005

I will check the tank vent and I will lower the fuel level slightly in both bowls and see if it changes anything. It's getting hot here today so I will have a chance to try out some ideas. thanks

2nd Mustang · Aug 13, 2005

67bluegt said:
It shows up most when you turn a corner, then the engine dies for a second or two. Any ideas?

I noticed from later post that you stated you have the pump mounted on some straps. I had an another 65 coupe with an electric pump mounted to the frame near the rear tires and I think I remember that the pump got it's ground source from the body of the pump. Is your ground source clean and firm?

67bluegt · Aug 14, 2005

That's a good question. I think I will climb under and check out the grounding. It was not the best if I remember. Not sure how only hot days would trigger it, but it's possible. thanks

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