I just finished a putting a rebuilt 390 in the 61 Ford and the only real problem I am having is vapor lock (I think). Here is what happens: Have about 450 miles on engine, Runs fine, temp is always good, but then I stop to get gas or something short like that, re-start the engine and the temp goes way up for a short time. If I try to drive immediately, it will start to sputter in a few minutes. If I nurse it, it will stay running, and then it is ok. By that time the temp is back down where it should be. This all happens in about 5-10 minutes. It is basically a stock engine with a performer manifold, a 600 holley and a new mechanical fuel pump. It also has a 1" plastic riser under the carb (mainly to avoid vapor lock). Everything under the hood is new or rebuilt. I believe this is vapor lock and the heat soak from the engine is boiling the fuel out of the carb or the fuel line. Please let me know if you have any ideas on how to remedy this problem. Thanks -Dave
It does sound like vapor lock but I'm confused by what I've copied from your post. Normally vapor lock is caused by the gas boiling from your carbs as you've stated...but in the first sentence you say that if you try to drive it immediately it will start to sputter in a few minutes. That doesn't sound like the fuel has boiled out of your carbs...it sounds more like a fuel pressure problem.
Sounds like your on target with the troubleshooting. The only thing I can thinks of is putting a bypass fuel filter on it and run a return back to the tank........If I recall, just before FI took over, car manufacturers did just that because of high temp thermostats (meet emission standards) and high under hood temps. Hot soak seems dead on. When you park it hot try lifting the hood and see what happens
Yeah but this is about 25 or so years before FI took over. If your pressure is inadequate, and just as with coolant, your fuel will vaporize at a lower temp. Good place to start.... Fuel gauges are cheap. Hook one up and monitor it under all conditions.
25 years ago, we routinely changed to a 160 degree thermostat in the summer.........fuel was formulated differently too. It has a new pump on it, but yeah, check the pressure..........ir blame it on global warming.
the engine temp going way up is a different problem. Although this could be causing the vapor lock. Does the temp climb as the engine is shut off or immediately upon start? i would suggest trying a new or different thermostat. Sounds like it's lazy or sticking. How hot does it get? The sputtering and starting issue does sound like vapor lock. Is you carb hot to the touch? is the line? Does the line come close to the exhaust or is it touching the motor? I've had vapor lock on 2 vehicles, both have which have been problems with the line running to close the the block (although again yours seems to be related to a high temp issue). A simple reroute has done the trick in both cases. My daily drive piec o shit 86 pickup also gets vapor lock from time to time, again a line clearance issue. The carb is off a van which has a center fuel inlet and comes two close to my thermo housing. Sometimes it's hard to start after a long haul so pouring a little poland spring on it always does the trick. I'm too lazy to fix it and the truck barely deserves it's anual oil change so fuck it... good luck
they used to put wooden cloth pins on fuel lines a long time back, for vapor lock, i dont know if it work or not, not a joke
I would switch to a Holley Red pump (don't need a regulator) and Chevy use to make a heat shield that went under the carb. It was a piece of flat aluminum that went under the carb to isolate it from engine heat. Should work for any Holley.
I can confirm that the heat shield will work. It cured my '73 from the vapour locks, exact same circumstances as the OP. Alex.
Mid 70's Ford pickups with 360's and 390's are the worst vehicle I have ever seen for vapor locking. On the stock setup it seemed like the gas was boiling in the line right around the mechanical pump rather than in the carb.
I believe it My friend used a 46 ford with a flathead 8 back in high school and when we delivered newspapers with it each afternoon it would vapor lock. He carried a spray bottle of water and would spray the rear mounted pump on top of the engine, plus the line to the carb. Had to do that several times a trip. Gas today is even easier to vapor lock
You are right, it may be a fuel pressure problem, it seems to start and idle fine but when you try to drive it, it acts like it is running out of gas for a short period (maybe till it cools down). Seems to me it would act like that whether the fuel was boiled away in the fuel line or in the carb. either way, the engine is not getting any gas.
The temp climbs as soon as I shut the engine off. But I don't think it could be the thermostat because it keeps the engine at the right temp all the rest of the time. When you think about it, this makes sense, normally when the engine gets hot, the thermostat opens and all the hot coolant gets pumped thru the radiator so it can cool off. Whe the engine shuts off, there is nothing to pump the hot coolant out of the engine so it would heat up to some degree. I do not know how hot it gets because there are no numbers on the gauge. When I turn the ignition on it pegs the meter, but then comes down within a few minutes of the engine starting. Also, it never dumps coolant out the over flow with a 13# cap. I am sure someone could figure that one out. I can also check the temp of the carb and the fuel line As you can see in the pic, the output fuel line runs right next to the front of the engine. this may be a problem. Thanks for the input !! -Dave
I do not know, I am going to T a pressure gauge in line and see what I get. Lots of other good sugestions too. I think the best thing to do is check temps around the fuel line and find out where it is the highest, then move that area or insulate it somehow and see what happens. if this does not work, maybe change the thermostat and see what that does. Thanks -Dave
Keep in mind that until the carb itself cools down you're going to keep sputtering. The cooler fuel from the fuel tank flowing through is going to bring its temps down, but that is time dependant as the fuel is going to flash the second it reaches the hot carb (why you can run a few minutes sometimes until it acts up) until it is cooled sufficiently. Got a piece of sheet metal? Cut a square hole in it to fit the outside of your carb holes, an extra gasket and sandwich it in. Make sure your linkage doesn't bind and take it for a test run. Alex.
If you have enough hood clearance, a phenolic carb spacer will keep your carb much cooler. I just installed one on a 302 Ford in a 51 Mercury yesterday to help combat a similar issue. In that case, the fuel lines all needed to be re-done as well. Someone had routed miles of rubber fuel hose all over the engine and near the exhaust to keep it plenty warm!!!
Good point, I will keep that in mind. The plate looks like a simple quick thing to do as well. I have a spacer under the carb now, not sure if it is phenolic tho. Anyone know how hot a fuel line or carb can get before it boils the gas?
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