Weak fuel pump?

[67Dart273]

Red, since you are having such a fight, I think it's time "to get serious."

I assume you have ONLY a mechanical pump?"

Put your pressure/ vacuum gauge back at the rear and crank the engine. It should pull at least 12" vacuum

Now unhook the line to the carb and devise a way of plugging it quickly. The best you might be able to do is a bolt with a smooth unthreaded section, and a clamp.

Again crank the engine, develop vacuum on the gauge, and as quickly as you can, plug the front carb line and clamp it.

Now watch the gauge for leakdown.

This business of the "empty filter" may be a red herring. The fuel may be trying to boil, and as the needle opens, the fuel suddenly expands and vaporizes, until the pump keeps up. I've seen lots of cars that ran perfect with a partly or completely empty filter, although if you run it a couple of minutes you can see fuel "coming and going."

Even though you replaced the pump, have you run a capacity check? You may have a problem with the eccentric.

And don't forget--"new" does not mean "good." The new pump might have a problem. OR if it got a little dirt into it, the pump valves may not be working

 

[RedFish]

Here's what I've done.. While waiting for the Carter paump to arrive from Rock Auto i pulled a 3 year old air tec from the 73 Valiant 318 and bolted it on the 273. Hard line port in different orientation along with fuel filter location. Pulled the hard line from the Valiant and installed on the 273 with brand new mopar inline filter that cant be seen through. It is now positioned vertical below the alternator. Replaced rubber fuel line at pump to frame rail and replacd the short one at the tank/sender. New clamps all around.
No difference what so ever.
Installed dual plane intake from Valiant 318 on the 273. Tuned, drove around a bit. I cant exactly say no change in overall performance but the original problem still exists.
Yesterday I rechecked intake torque, installed that new Carter pump. I really hoped to hold back that pump for the Commando build. Oh well, still no change.
I can no longer see fuel comming and going but I'm sure it is. The stumble, and fluxuating rpm at idle, fish bite of a mis unde light throttle/load remains unchanged. Runs right well under load/WOT. Got a match ? LOL

 

[airwoofer]

You could test your pump by running the gas line up front into an empty 2 gallon gas can, it should darn near fill it in a minute. I believe that pump you're running free flows at 125 GPH. If it does then the pump is probably OK.


I tested my elec pump last night by removing the fuel line at the carb and flowing into a can with the elec pump. It took 1 1/2 minutes to flow 1 gallon and that is with no restrictions the carb induces - ie with the pressure gage reading zero cause the line was just dumping in a can.

I am thinking the pump is weak or the stoick gas line is too small. Might not even be flowing enough for the little 340 at 6000 RPM. The stroker I bought has dyno sheets calling for 38 GPH so definately will have to be fixed before putting that in the car.

 

[RedFish]

The psi comes from resistance. With the line full open you would see very little or no pressure.
If 125 GPH is correct, that's about 2 gal per minute, and you got 1 gllon in well over a minute... thats half gassed. Pardon the pun.

I think I found my problem to be the bowl vent not opening. Makes me feel stoopid too. :banghead:
I'll know for sure in a day or 3. It runs so smooth right now that I can idle it down to dang near nothing and ride the rockers / adjust the valve lash.
I'll paint and reseal the rocker covers too while waiting for the parts needed back at the fuel tank.

 

[Ksipes1]

It use to run fine....it just started acting like this not long ago and progressively got worse to the point it is now.

yeah I know the ole gas can trick....just wanted to get some opinions on it first before I go out and take it apart and get splashed with fuel lol.

but thanks for the input!

I also thought about disconnecting the feed line to the pump and capping off my vent line and try blowing air down the filler neck to build pressure and send the fuel down the line in the bucket to see if any gunk came out.

someone put a new tank and filler neck in the car at one point.

the car sat for a good 2 years....when I first put gas in it I seen some rust particles in my fuel filter but cleared up not long after.

Ill go through trial and error and save dropping the tank as a last resort if I have to.

I had similar issues where very small particals of rust got through the filter and enough to mess up the carb. Cleaned the carb and it was better. Put in new tank and sender. Ended up putting in a wood spacer to help with the heat soak that seemed to be causing some vapor lock. Was better. Finally put in an electric fuel pump and problem solved.

 

[Dusterdude72]

I just finished up moving to a new place and I ended up driving the duster to the new place. When I got in the home stretch of the new place I decided to get on it and see if it fell on its face.......boy was it the opposite, the duster turned on so hard and was gone in a flash......no hesitation,no bogging,nothing.

so I think the 15 mileish drive of steady 40mph driving may have loosened some rust that may have been clogging the screen in the tank or something.

fuel pump would not be intermittent like that....so I am thinking the tank needs dropped and cleaned out and should be good to go.