Going off subject for a few minutes: Thank you. I just want to say that my truck is what it is today because of you guys. I learn so much from reading your posts and there is no place on earth to get this level of knowledge, mutual respect, and humor. Sometimes I can't find what I am looking for searching in FTE so I browse other forums. You get two comments in and they are bashing each other and the original poster is not helped.


I am creating this new thread because I wanted to share my experience. I do not have all the answers but I have a few. Within the last month I started driving my truck to work and other places (current mileage is 397 miles). It is not finished (probably will never be finished) but enough for me to start enjoying and working out the smaller issues. I have driven to work about 5 times thus far (13 Miles). Early Texas Fall mornings (70~ degrees) and evenings (80-90 degrees) with no issues. I drove home and did not drive it again on those days.


On Monday I drove home (91 degrees) got my son and we drove to the Homecoming Parade. I was not in the parade but sat on the tail gate with my 9 year old son. I could go on about how incredible that was but I do not want to go off subject more than once. After the parade was over (1 1/2 hour) I got in the truck but it would not start. Thought I was out of gas however, I just put 10 gallons in on Friday. No gas gage and that is why I carry a one gallon gas can. I poured my gallon in the tank and cranked it until it started. Went straight to the gas station to put 10 gallons back in but before I got to 10 it was full (22 gallon tank).


Tuesday I also drove to work. After work I picked up my son and went straight to Baseball practice (91 degrees). After practice (still 90~ degrees) the truck took three attempts to start in the same manner as Monday. In the morning and when I leave work my truck starts right up with zero issues. Sounds great, idle great, and everything. What came to my mind after these two days was Vapor Lock.


For you to get a picture (and I will attach) you need to know about the truck.

• 351W - Totally rebuilt with mostly stock parts (except new Edelbrock 600 carb-manual chock) couple years ago
• Mechanical fuel pump
• No A/C
• No Heater
• No Power steering
• Only belt going from crank to water pump to alternator
• Intake Manifold is cast iron and is original to the engine (from 1985 F-250)
• 165 Degree Thermostat - This weekend's work to change back to 180 Degree thermostat. Truck has been operating between 160-190. I understand this to not be efficient operating temp for engines so this is why I am changing. Just learned this through the vapor lock issue which may only exacerbate the issue.
• Only one Clear Fuel filter directly before pump. Many discussion I have found on whether the filter be before, after or both. To me it just makes since before but who knows.
• Filter screen/sock in fuel tank
• Combination of metal line and rubber hose between fuel pump and carb
• Fuel line running from fuel pump and carb runs within inch of front of engine and intake
• fuel line from tank to fuel filter ran in C of frame away from heat
• mechanical fan from engine belt drive
• exhaust manifolds
• new 22 gallon fuel tank (basically everything is new on this build except for frame and sheet metal)
• one inch aluminum spacer between intake and carb

I may be missing some details that are important for you to get the picture.


In my searching it seems that my gas is vaporizing in the fuel line via heat soaking when the engine is off for an hour or so until it has time to cool like the next morning or at the end of a work day. Considering the close distance of my carb to the cast iron intake even with an inch aluminum spacer and combination of rubber and metal lines I think this is a culprit. I also do not have any way for the heat to escape like vents in my engine compartment and heat rises and sits there. The last thing that I believe is causing the issue besides the ambient temp is that Ethanol gas I use. Only one Ethanol Free station in a 100 mile radius (30 miles away from my usually location) in my Dallas-Fort Worth, Texas area. I understand that Ethanol lowers the boiling point of the fuel and also the fact that a negative pressure is created by my mechanical fuel pump which also lowers the boiling point of a liquid.


Here are some things that I do not want to do to correct the situation:

• Cut a hole in my hood to vent heat - opens other issues and just looks bad IMO
• Only use Ethanol gas - unrealistic to travel that far every time
• Add an electric fuel pump - I do not want to whine and any electrics I do not have to have on the truck
• Add an electric fan that stays on after the engine shuts off - same reason as not wanting electric fuel pump

Here was some changes I am going to make:

• Reroute the fuel line from the fuel pump to carb away from engine
• Change the material of the fuel line from the fuel pump to the carb from metal and rubber to something less heat absorbent. I have read that black nylon fuel hose is the way to go. Still researching.
• Future (need to save money) - new Edelbrock Performer RPM Air-Gap Intake (7851) - This being aluminum will help a lot and if am being honest will make my engine look great. I was going to make this change sometime but I am a guy that live by if its not broke...

I think the above major changes will provide cooler temps for the fuel in the fuel line from the pump to the carb and the fuel in the bowl of the carb when the engine is shut down. I do not think at this time the issue is with the fuel in the line from the tank to the filter. I may add to the list to move my filter farther from the pump/engine and more into the C of the frame.


Thanks for reading and any replies.
Stephen

 

I can tell you my experience here in Tucson. Huge problem with my daughter's 66 Mustang with SB engine. ONLY during peak heat of summer.

Very similar setup to yours but a 302. Blocked heat riser passages in intake, phenolic carb spacer, silver heat wrap on fuel line in engine compartment, air deflector in front of carb to divert fan blasting hot air on fuel bowl. Helped but did not eliminate problem on the really hot days.

The fuel tank gets scary hot here in the desert. It is the trunk floor in a Mustang so a heat shield at least deflects engine and road heat past it.

Ended up installing an electric pump near the tank to push through the stock mechanical. No more problem.

The thing I cant figure out is why my other daughter's 66 Mustang didn't need ANY of these mods. Same car, same engine. Only difference is one has a C-4 trans and the other has an AOD. Maybe additional heat from trans into rad?

My completely stock flathead in my 52 doesn't vapor lock in this heat. The gas will evaporate out of the carb over a few days though.

 

Yep, I haven't heard of anything but an electric pump being successful. There are many that aren't noisy. 12 years with mine and no issues, no heat soak problems, and I run E-10 all the time in high temps, high altitudes (which are even worse)

 

I learned a trick driving Willard cross country in 1978 in the summer while flat towing a model A. At that time Willard was running a 56 Buick Nailhead. Clip a number of common spring type clothes pins on the steel fuel lines in the engine bay area. Given your engine/fuel line layout about 20 pins should do it.
It did really work and was an old time fix.

 

A easy fix is using an inline gas filter between the carburetor and fuel pump. When the gas goes through the filter it is cooled enough to prevent the vapor lock. I used this method some years ago and it worked fine. In the old days, wrapping the fuel line with aluminum foil as well as the old clothes pin trick was popular...

 

Interesting. I always figured a filter in an area of high heat would allow more fuel to remain in the area subject to high engine heat and make vapor lock more likely. I don't know.

 

To fix the problem on my 74 k5 I had to run new fuel lines from tank to carb, crap stuck in the lines added to the problems... was able to get rid of the electric fuel pump that the PO put on it.


Good luck.

 

Vapor lock does not occur past the fuel pump. Once the fuel is under pressure it's going to make it into the carb (unless you have an ancient carb that has an unvented bowl - the AFB in your pic is most definitely vented.) If the fuel on the suction side becomes hot enough to boil/vaporize (100° F and up, depending on atmospheric pressure and fuel volatility) the voids (bubbles) are difficult for the pump to pull. If you have an older mechanical fuel pump it may also exacerbate the problem as it might not be able to create enough vacuum to pull the fuel from the tank. Likewise a small leak an the tank side will decrease the pumps ability to pull. Pumps always push better than pull. A non-vented fuel tank cap, or even a vented cap that's not performing properly, will add to the problem. 22 gallon tank? Mounted at rear of truck? That added distance would make the draw more difficult. Height of fuel tank vs. fuel pump height can also create a problem as the pump has to pull the fuel to the top of the tank and sometimes pull up again if the pump is higher than the fuel line mounted on the frame rail. While I also prefer a filter on the suction side it does add to the difficulty of the pump to pull fuel. Sometimes a bunch of little things add up to a problem.

 

I noticed in your description of your engine set-up that you still have the original Intake Manifold - If I'm not mistaken the manifold and exhaust set -up had a heat riser in the exhaust. I would investigate if the heat crossover passage is still open. If so , it can also cause excessive heat buildup in the intake and cause a hot soak or boiling of the fuel in the carb. Also check in your area what the RVP of the fuel is. Although this is supposed to maintained at the refinery level and changed per season for each area it can vary and with today's fuels increase fuel problems in carberated engines.

 

In my case, the evidence indicated that my vapor lock was occuring down stream of the original mechanical pump. Clothpins were clipped in the fuel line between the pump and the carb which made all the difference. I do not know if the original fuel pump was performing per design, I only know how dramatic the change was after clipping the clothpins between the pump and the carb. It is so easy to do that I suggest that the OP does this first.

 

I remember my dad using clothespins on his 48 flattie.

 

In the case of the flathead V8 with the fuel pump up high, the clothespins would be placed on the suction side of the fuel pump.

 

I'm old enough and have been working on cars and trucks long enough to remember clothes pins on fuel lines. I remember people in Ft. Lauderdale, where I began working on cars professionally, using them on totally flat ground at a whopping 8' above sea level. LOL I can only recall ever seeing vapor lock occur on several vehicles and they were all tightly packed motor homes, in the Colorado mountains, while struggling up mountain passes. But that's just my experience and I haven't seen everything.

I'm not going to argue whether they worked or not. However, as a thermal conductor, wood isn't one. It's a thermal insulator. I'm thinking wrapping something reflective, such as aluminum foil, around the fuel line would probably be a better option.

 

Clothespins do work as I have a fire pump with a Chrysler flathead 6 that requires clothespins, and it has an electric fuel pump. I don't know if it will help with your truck, but it won't cost anything to try.

 

The guys on the Ford Barn have so much trouble with VL that there are many threads about it and how to eliminate it. Unlike our trucks with the tank in the cab, the Cars had tanks mounted low and at the rear. The long lines exposed to heat, and the higher lift to the pump, cause real trouble for them.

One of the guys on there measured the temperature of the fuel pump housing after shutdown, on a warm day. It was near 160 deg. The FP absorbs heat from the intake manifold and engine bay. You could run ice-cold gas into the FP and it would just flash off at that temperature. Clothespins aren't going to make any difference in that situation.

They've also measured carb temps in the 130's. Ditto.

Adding a fuel filter that has a return line connection just ahead of the carb to circulate fuel constantly back to the tank, and to allow vapor to escape, helps a lot. Lots of cars used these, and if you have a return connection on the tank, it is worth trying. But like I said, the only reliable way to eliminate VL is to push the fuel from the tank to the carb, with an electric pump.