Electric Fuel pump options for heat soak/vapor lock problems

[CudaJon]

Happy Summer,

I have a heat soak/vapor lock question regarding my 73 340 stocked Cuda.  I need to solve this problem since it's getting embarrassing especially at the gas station.  Since I have an iron cast intake and was told from "Coolcarb" that the thermal insulator solution may melt due to the heat generated and the crossover port that I'm now thinking of just putting an inline electric fuel pump mounted near the fuel tank. The problem I seem to be running into is that I'm looking at Carter fuel pumps and their all require 3/8 fuel line. My SB has 5/16 fuel line. I certainly don't want to change out the sender unit and replace to a 3/8 fuel line. Does anyone have any recommendations on fuel pumps or just solving this problem the least expensive way.  Thank you very much for reading!!

[Dakota]

I can't answer your question with confidence, but it might help those than can if you add a few details about your approximate HP and how you drive. 

For a stock motor that's street driven (no racing or autocross), I'd think the 5/16" is adequate as shown in the attached screenshot from Summit, but I'd certainly defer to the wizards here.  Note that the Summit chart includes the words "if your pump manufacturer doesn't specify" except that yours did. 

[DeathProofCuda]

Happy Summer,

I have a heat soak/vapor lock question regarding my 73 340 stocked Cuda.  I need to solve this problem since it's getting embarrassing especially at the gas station.  Since I have an iron cast intake and was told from "Coolcarb" that the thermal insulator solution may melt due to the heat generated and the crossover port that I'm now thinking of just putting an inline electric fuel pump mounted near the fuel tank. The problem I seem to be running into is that I'm looking at Carter fuel pumps and their all require 3/8 fuel line. My SB has 5/16 fuel line. I certainly don't want to change out the sender unit and replace to a 3/8 fuel line. Does anyone have any recommendations on fuel pumps or just solving this problem the least expensive way.  Thank you very much for reading!!

Can you tell us more about the problem that you are experiencing?  Car doesn't want to restart when you just shut it down for a few minutes to fill up at the gas station?

[CudaJon]

I apologies for lack of detail. So the car starts great from a cold engine with no issues at all. However if I wait about 10-20 minutes after the car has been warmed up - driven, it has a very tough time starting. It's only with I have the petal all the way down that I can finally get it going and I'm hoping my battery and or starter does not fail. I did some experiments where if I wait say 30 - 40 minutes, I have no issues,  it starts without the petal to the floor. When I do take it for rides I often just pop the hood, and knowing I will be there for at least 30 minutes, the car will start. I guess I convinced myself it's heat soak because it's very repeatable. So that goes into my thinking in that if I could try something like a electric fuel pump inline, I could quickly rule it in or out. Thanks!

PS: I go to the same gas station and usually chew the rag with the mechanic and forget about the time. It just happen once. 

[DeathProofCuda]

What is your procedure for starting the car when warm?  Does it turn over slower when warm than it does when cold?

[CudaJon]

Yes, so starting the car warm, I depress the petal almost halfway and turns about 4 times before catching. Sometimes maybe 5 times, sometimes maybe only 2 times. Hope that helps.

[DeathProofCuda]

Yes, so starting the car warm, I depress the petal almost halfway and turns about 4 times before catching. Sometimes maybe 5 times, sometimes maybe only 2 times. Hope that helps.

So you depress the pedal about half way, turn the key, the car turns over 2 to 5 times and then starts, is that right? 

Not trying to be a PITA, just trying to cover the basics because I'm not sure that an electric fuel pump is going to do anything to remedy your problem.  Have you taken off the air cleaner and looked down into the carb right after shutting it down?  You may have gas boiling out of the fuel bowls, flooding the carb, which is why you need to floor it (completely opening the primary throttle blades) to get it started.

Many warm-start starting issues are also due to additional resistance in the electrical starting system due to heat.  Sometimes the starter turns over just slowly enough when warm to cause a problem.   Sorry if you've already covered all of that.

[CudaJon]

First off you are not a PITA, I appreciate yours and all members input. I'm not a mechanic so I need to be asked these questions.


Yes! you got it on the petal.  So I have taken off the air filter I believe last summer and honestly forgot what I found. (That doesn't sound good...)  This weekend I will get the car warmed up and take the air filter off.  Will I hear the fuel being boiled out?? I also have a spark plug wire with a light to show if I'm still getting a spark, I will also try this to make sure the electrical system is not the problem.  Can you recommend anything else I should try?? thank you very much!

[7212Mopar]

If you keep the stock 5/16 fuel line and new fuel pumps are 3/8, just get some reducers. Get an insulated carb base gasket if fuel is boiling when engine is hot.

[FSHTAIL]

Using non-oxygenated fuel cured a lot of that issue for me,
also using a phenolic carb spacer solved the rest of it. 

If your fuel has ethanol in it, you're not going to have a good time. 

[torredcuda]

If you are holding the pedal all the way to the floor that usually means the engine is flooded with fuel not starving for fuel or vapor lock. What carburator, stock Thermoquad?

[CudaJon]

The Carb is an Edelbrock, I believe the model is 1806S but could be wrong. - Thanks

[73_Cuda_4_Me]

@CudaJon - So if you are running an Eddy (Probably the 1406s like I have), then you also have to have an adapter to go from spread bore carb to square bore...

What other engine info can you provide? You say stock 73 340, but have you added a cam or headers? What is your timing set at?

I had the same issues you do, and most of it was advanced initial timing making it harder to start, and also causing more heat in engine compartment with headers.

[GrandpaKevin]

Running Mopar electronic ignition?
Check for spark when the hot start issue happens.

Had the same hot start issue years ago.
Spent a day trying to vapor lock proof my fuel system with no luck.

Old time Mopar mechanic told me to replace the magnetic pickup in the distributor....
Replaced the magnetic pickup and never had a hot start issue again.
They fail often and will work/start when cold but once warmed up will not work/start again until they cool down.

Good luck

[Poolshark314]

A simple thing to try that has seemed to be an improvement for me is using heat wrap on the fuel line into the carb. You can find it for less than $15 usually and it takes a few minutes to get on, depending on how far down from the carb you want to go.

As a side note, if your 340 is running a cast iron intake manifold, hold off on the Coolcarb for now. I am talking to the owner about troubleshooting my issue. He has been great so far and is sending me some things to try out. I will keep you posted if it still interests you