Hey guys, I just bought a 71 elco, and its got a 5.7l carbureted block mated to a th350 tranny. I believe its either a 600 or a 650 cfm edelbrock carb.
Here’s the problem: after starging right up with a little accelerator nudge, the engine idles fine; after warming up, i take the car out in the city. Runs fine. I take it on the highway, and it accelerates up to crusing speeds. After about 10-15 seconds, the engine begins to stall out and die. Ive found that if i deccelerate slowly, the engine keeps turning over, but coughing and sputtering. I need to pull the car over because of traffic. The engine settles down and mostly returns to normal. I take off fine giving it a little gas, but like previously stated, up to highway crusing speeds stalls the car.
A couple things- I thought it might be the fuel delivery system (changed the filter, monitered the fuel pump; it sucks in a good way)
also, the transmission’s first shift point seems to be a little too high. second gear shifts through very very quick into third, almost unnoticable. I dont know if the throttle valve is the cause of all this mess.
From doing research online, most symptoms point to the accelerator pump, but I want some advice before I dive into the carb
The accelerator pump shouldn’t cause it to die after getting up to speed. When was the carb rebuilt? Could be bad float adjustment, bad float, something preventing enough gas into the carb at high speed.
Sounds like fuel starvation, flow-test your fuel pump. It should deliver at least a quart a minute, or even a half gallon…Disconnect the fuel line from the carb and stick it in a jug and start the engine for 30 seconds and check the fuel flow…
I agree with texases & caddyman. Definitely fuel starvation. Is it possible this was a six cylinder car originally? If it was, it may have used a 1/4" fuel line, which may be too restrictive to feed a 350 at highway speeds. It should use a 5/16" line at a minimum, and preferably a 3/8".
This vehicle likely does not have a fuel return line to the tank. Is it possible the car has a non-vented gas cap on it and the pump is trying to pull a vacuum on the tank?
If so, you might remove the gas cap, drive it a ways, and see what happens.
Another possibility could be the carburetor floats being set too low.
Have you checked the fuel filter…Like many GM vehicles of that era…the fuel filter was built into the Carb and was ridiculously small…Check the filter…If bad…remove and replace…Better yet…is to remove it and put a better Fram F1 Filter in-line. That’s what I did on every GM carb’d vehicle I owned.
It’s not a Quadrajet carb.
I think it’s a bad coil. How old is the coil?
Does it still have points?
For the shift points try adjusting the throttle linkage/cable going from throttle to trans.
If the fuel pump has 3 outlets, one is a return line to the tank where a pressure regulator allows for fuel to recirculate to prevent vapor lock. If the pressure regulator fails in the open position it will cause your problem. If there are 2 rubber connections at the pump going to the tank pinch off the smaller one and test drive at speed.
Unless I’m very much mistaken, the shift points are determined by the governor and the valve body. The cable between the throttle and transmission is for manual kickdown (passing gear).