Engine miss at 30 MPR

[JimT]

i have a 1956 292 that runs good but at 30 to 40 MPR it will fall down like it out of fuel. I have put a new coil, new power valve, change the old gas. I need help

[Daves55Sedan]

BTW...it's MPH (miles per hour).
Could be that your float is set too low, so that the more gas you use, the closer your float chamber gets to empty, so the engine starts sputtering.
If you have done a carb rebuild, go back and look at the float adjustment instructions that come with the carb rebuild kit. There are a couple different versions of the needle, seat and washer(s) depending upon whose kit you buy, so you must use the instruction sheet from the exact carb kit it came in.
It is very easy to adjust the float on a Ford 8BA, EBU, Holley 2100 or ECG carb (Holley 2110). Just take the top (air horn) portion off and turn upside down to gain access to the float and use the cardboard measuring stick that came with your rebuild kit.

[Merc Cruzer]

Sounds like fuel starvation.

[54vicky]

to confirm fuel starvation when it starts to do that ease off the throttle.do not lift off the throttle but slowly ease off it will allow fuel to fill the bowl if it is the float setting.then slowly ease into it see if it keeps up.another thing you can try if you have a manual choke is pull the choke out slowly while driving when miss starts this will change the air fuel ratio.good luck.there may be a problem elsewhere in the fuel delivery system (hole in fuel line etc)

[dmsfrr]

The rubber hose between the fuel line on the frame and pump may be obstructed inside. Age and ethanol can ruin them. Check the output pressure & flow of the fuel pump if you can. (keep a fire extinguisher nearby)

Which carburetor and distributor does the engine have?
If the engine has an original 'Loadomatic' distributor you may not be getting any timing advance. When the rubber diaphragm in the vacuum canister goes bad the timing advance does not work at all.
.

[bobss396]

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2X on the fuel hose thing. When in doubt, change it out. Get some ethanol-friendly hose and new clamps. Also the fuel filter, avoid the glass or plastic ones that I see too much of.

What carb is it, a Holley? They are easiest to set the floats on.

[rotorwrench]

I've even seen stuff in a gas tank get sucked over to the stand pipe and block it under acceleration. Any flex line that feeds the fuel pump can either have blockage or even a hole in it. Under suction draw it will leak air into the line.

The jets and main fuel metering passages in the carb may have a problem with blockage to fuel or air vaporization flow. Some of the new power valves don't fit the older carbs well. The accelerator pump has to function correctly. Older carb bodies can get warped or have worn throttle shaft bores due to age and shade tree maintenance. Load-O-Matic spark control has been mentioned but this was a system that utilized the carburetor as part of the system. The ports for venturi suction to operate the system also have to be in correct configuration in order to function the diaphragm in the distributor as designed.