Fuel problem

[Jim Yergin]

I have a 1956, 312, manual transmission. Running fine except when going up a steep incline it will act as if it is running out of fuel. If I turn on my auxiliary electric fuel pump it will return to normal. I rebuilt the original mechanical fuel pump with a kit from Then and Now and It now does run better but still a problem on very steep inclines. Any suggestions will be appreciated.
Thanks,
Jim Yergin

[ward 57]

I'm thinking carb fuel float too low.

[Jimntempe]

I have a 1956, 312, manual transmission. Running fine except when going up a steep incline it will act as if it is running out of fuel. If I turn on my auxiliary electric fuel pump it will return to normal. I rebuilt the original mechanical fuel pump with a kit from Then and Now and It now does run better but still a problem on very steep inclines. Any suggestions will be appreciated.
Thanks,
Jim Yergin

If it never does it with the electric pump on it seems unlikely the problem is in the carburetor. I had my mechanical pump rebuilt by highly regarded rebuilder and it will still run out of fuel at times but the electric pump always takes care of the problem. How warm a day is it when you have these issues? Could be the ethanol is borderline vaporlocking.

[Rusty57]

Some electric fuel pumps can create enough pressure to force the float needle valve off the seat. Don’t ask how I know!

In that case the electric fuel pump hides the fact that the float level is low.

Have you checked the fuel level in the float bowls when the car is idling with just the mechanical fuel pump?

[Jim Yergin]

Thanks Rusty. Planned on checking the float level. The factory manual talks about "sectioning" the top cover on the carburetor to check the float level. Not familiar with that term, Doses it mean "remove?"
Jim Yergin

[Rusty57]

Hi Jim,

I apologize for my big mistake. I just reread your original post and realized that your car is a 1956. Lately my mind has been so focused on various ‘57 Holly 4 barrel issues that it automatically went in that direction.

I do not think you carburetor has the fuel level check plugs like the ‘57 4 barrel. So I assume that you will need to remove the float bowl to check that.

Once again, my apologies for creating any confusion. Hopefully a ‘56 carb expert will offer their advice.

[Jim Yergin]

Rusty,
Absolutely no need to apologize. I appreciate the guidance.
If "section" means remove then I think I can handle it. I will report back on my results,
Jim Yergin

[Rusty57]

I agree with your interpretation of "section".

[Jim Yergin]

On closer reading of the manual, the sectioning it calls for is actually cutting a spare cover to be installed so as to have access to the float level.
Does anyone know if I have to do that or may I just run the engine without the top cover on the carburetor?
Jim Yergin

[Rusty57]

Hi Jim,

Not sure I have a direct answer. Based on what I can see you need the “sectioned” cover so fuel is delivered to the bowls so you can observe the fuel level while the engine is running. The fuel comes up the 2 tubes that connect to the cover.

You might want to spend some time watching the YouTube videos from Mike’s Carburetor on rebuilding a Holley 4000. They are a very reputable shop. I have purchased from them and used their videos to rebuild a carburetor.

https://www.carburetor-blog.com/articl ... lley-4000/

[voltron]

I had a teapot do the same thing. You don't check the fuel level with the engine running. Holley manual says get car on level ground remove top cover of carb and, pull coil wire to disable, crank engine over with starter to fill bowl. The fuel level should be 1/2 inch below top edge of carb, without the gasket. Mine was off by an 1/8 inch too low and It would quit on local a bridge. Raising the fuel level an 1/8 inch fixed it.

[Jim Yergin]

I raised the level but it did not cure the problem.
Next I plan on pressure testing and flow testing the mechanical fuel pump.
Jim Yergin

[Jim Yergin]

The pump passed the pressure test but failed the flow test. The shop manual says it should produce a pint of fuel in 30 seconds or less. Mine only produced 1/2 pint in 30 seconds. To make sure it is not a problem in the line from the tank I bypassed the mechanical pump and ran the input line to the carb so that I could run the engine on just the electric pump. I then ran a new input line from an independent gas can to the mechanical pump with an output line to a container then ran the engine and the mechanical pump still only produced 1/2 pint in 30 seconds.

So it appears my fuel starvation problem is with the mechanical pump. However it is a freshly rebuilt original AC pump. I called Then and Now for advice. They suggested it might be a problem with the gas cap not venting properly. However my use of an independent source of fuel eliminates that possible issue.

Does anyone have any suggestions on where I go from here? Did I do something wrong on the rebuild that would cause a weakened flow? Is it possible that the lever on the pump is not getting a full throw on the drive cam?
Jim Yergin

[Rusty57]

Hi Jim,

Good testing procedures so we have actual facts to consider, not just speculation.

You eliminated an inlet restriction as an issue. The fact that the pump passed the pressure test means that the diaphragm and check valves are ok. So that leads to the stroke not being adequate.

Often during a rebuild they often do not consider wear on the pump arm or wear on the pivot pin or the hole in the arm or in the housing. There is very little movement of the center of the diaphragm even when everything is in good shape. So any wear reduces that. The displacement of the diaphragm is what produces volume

[seany-boy]

Jim

Did you check the valve in the fuel pump after rebuild? I recall you mentioned about the press fit etc on the other thread but this was one of the symptoms I had before I reseated the valve.