Vapor lock

[Shakey Bender]

Hi all. A little background on the issues i'm having is in order I think. To start my fuel tank is original and has been giving me a little more than just gas. That said, I regularly change fuel filters (the big clear plastic paper element type). The issue I am having is when I really get on it I regularly run the bowl dry in the carb. There is air in the filter and it never gets much more than half full. Originally I had it between the pump and the carb. Now I have it between the hard line and the pump.
Sorry this is getting so long winded. But someone will probably ask these questions plus a few I'm not thinking of.
I tried this setup to eliminate the silt and garbage I found when I disassembled the pump and cleaned it out. Is a stock cam driven pump on a fresh motor better at pushing gas thru a filter or pulling? The pump is new and the cam lobe shows no wear. Some other things I have done, new hard line soft line and clamps removed the p/u filter cleaned out the carb and so forth.

 

[Bort62]

You are running the bowl dry under acceleration... what is your float level ?

Might be too low.

I have a hard time seeing how the filter could cause this unless it was extremely clogged, which it aparantly isnt.

What carb do you have? Some have a small filter screen on the inlet that may be cogged.

 

[wsa111]

Run, a fuel pressure test.
Perform a fuel volume check.
As Bort 62 stated, make sure your float level is not too low.
If all the above check ok, remove the fuel cap & blow with compressed air the fuel line at the fuel pump inlet. The sock in the tank may be clogged.
I would bet your fuel pump is the culprit.
By the way what kind of carb is on your ride?? Bill

 

[Shakey Bender]

Build info
3000 miles onengine since rebuild
74 200 block line honed 30 over flat top hsc pistons classic inline lopey cam 10/10 crank all new internals
65 200 head port and polished tricut valves 302 springs milled .020 valve stems machined for modern oil stem seals hardened seats multi angle cut
single out header into 2.25 with glass pack 1101 carb cable throttle 90 main jet ds2 ignition blaster 2 coil
The carb has no inlet filter and I have tried messing around with the level. I admit I don't know the correct means of measuring the float level. Some info here would be helpful. I suppose the pump may have failed but I will go back to the vapor lock issue first and has anyone tried any procedure for eliminating air in the line? The pump may be cavitating? By the way I removed the sock and filter assembly from the pickup.
Should I go out and buy a inline fuel pressure guage for the pressure test? Whats a fuel volume test? I wonder if the tank vacuum relief is clogged? Some how I think this is something simple. The car ran great until 2 weeks ago when I put some fuel treatment in and unleashed some deposits in the tank.

 

[BIGREDRASA]

Buy a simple vacuum gauge. Most will also read the pressure from the cam-driven pumps. The needle swings the other way, and you read the numbers opposite the fat side of the pointer. If you don't have a maintenance manual, go to the library and look up the Chiltpn's, Clymer's, etc.

To check flow volume, you basically disconnect the fuel line from the carb, and stick it into a 2 cup graduated measuring cup. What I don't recall for now is if you crank the engine for a minute or so, or you run the engine on fuel bowl contents for a minute. The book will tell you how much gas should have flowed into the measuring cup for the given time. Remember the old saying: "When everything else fails, read the book."

 

[Bort62]

Your pump isnt cavitating

 

[wallaka]

Your pump isnt cavitating

Yep, no possible way for a diphragm pump to cavitate.

I'd say that you might have a partial blockage in the fuel lines or pickup area of the tank.

 

[addo]

I'd also check the tank's vent tube for obstructions. Here, mudwasps love to clag them up with their nest.

 

[Shakey Bender]

Okay guys. Thanks for the help. I talked to one of my friends at work. He recomends a electric fuel pump. I looked this morning. They have a universal for 40$ a carter race pump for 90$ and a holley for 112$. I'm leaning towards the later two. I don't think the mechanical is gonna keep up with my motors needs in the long run. I will be stepping up to a 2bbl when the taxes are done. I want to get the problem resolved right. She is my daily driver aside from my motorcycle.
I will check back but I think/hope this will fixes me up.

 

[mustang6]

Careful with that electric pump- if the problem is really with fuel delivery from the tank as others have suggested (and I tend to concur with), the pump will not fix it and if you run an electric pump dry for too long you can damage it. You should be able to install it and try it long enough to tell if it fixes the problem though, and if you wanted to go electric anyway you could still do that after fixing the blocked pickup/line.

 

[BIGREDRASA]

What Mustang6 said.

 

[Bort62]

Yeah, I am pretty sure your problem isnt the pump, and throwing an electric pump on there is just throwing money at your car.

Especially since you already replaced the mech pump to no avail.

Open your fuel tank and disconnect the fuel line from the pump. Blow the fuel line out w/ compressed air. It may just be clogged in the pickup.

 

[addo]

I've killed two Holley pumps, due to non-return regulators. They keep pushing against the pressure, and fail internally.

The diaphragm unit as fitted to your motor by Ford, will support a mild 250.

Electric pumps need a return style regulator. Between that and the pump, you'll be in for a good $200 to $300 - a gauge is necessary, too.

For that matter, a fuel pressure gauge fitted now, will show if pressure is dropping under load... Perhaps that should be the next thing purchased?

 

[Shakey Bender]

I've thrown out a lot of info but may not have been detailed enough. The pickup is moving fuel and the hard line I replaced just days ago. The pump is moving fuel. I have run the car on the bowl and observed the flow from the disconected line. It had a pronounced pulse but all said it is working.
Okay lets back this up and go at it a different way. If say the needle and seat and or the float were set incorrectly or failed. If the fuel level in the bowl was say unregulated would this cause the engine to stall after a hard run? It starts and idles fine, will cruise well but, if I hit WOT for a sustained period It will stall on decel. It then starts back up after cranking for a short while or if I coast and baby the throttle.

 

[BIGREDRASA]

Okay lets back this up and go at it a different way. If say the needle and seat and or the float were set incorrectly or failed. If the fuel level in the bowl was say unregulated would this cause the engine to stall after a hard run? It starts and idles fine, will cruise well but, if I hit WOT for a sustained period It will stall on decel. It then starts back up after cranking for a short while or if I coast and baby the throttle.

That is affirmative. Also, if your carburetor is mounted sideways, it will flood when making hard turns. Try lowering the float say 1/8" and see what happens.

 

[Shakey Bender]

Thanks for all the help folks. Its back on the road. I did a complete tear down on the carb and found some dirt in the booster. My guess is at wot the dirt was getting pulled up into the passage and after it settled would start up and idle and cruise.
I did some leg work on the 2bbl conversion and found a 2100 1.14 for 25$. He even thru in a drop base 14 inch chrome air cleaner for free. It came off a running 68 289. I have ordered the adapter and a rebuild kit along with a half inch phenolic spacer. I will post results after the swap and tune. Can't wait!!