Those symptoms are consistent with a way-too-rich mixture. When you hold the accel pedal to the floor that activates the carb’s choke-unloader mechanism which turns off the choke; i.e choke is opened, disabled I’m suspecting gasoline is leaking from the fuel bowl into the intake manifold when the engine is off. Do you see any liquid gasoline coating the throttle valves if you peer down the throat of the carb before start up in the AM? Any liquid gasoline coating the surfaces of the intake manifold just under the carb? You may have to remove the carb to see that.
Another possibility is the carb’s idle circuits are clogged. That would make it hard to start & keep running at low rpms, but run fine at high rpms. Gasoline has two ways into the engine, first through the carb’s idle passages, which empty near the throttle valves, and second though the venturi, emptying near the top of the carb. The venturi pathway is only used at higher rpms.
If you don’t see any liquid gas (per above), you might try removing the carb, and remove the idle mixture needles (count how many turns), spray through those holes with carb cleaner, then replace the needles with the same number of turns (from closed). Might work.
Is your carb an Aisin with an AAP (Auxiliary Accelerator Pump) system? That has a vacuum hose going to a dome-shaped metal fitting held onto the carb with three screws. There’s a diaphragm under that dome. If the diaphragm breaks, there will be excess fuel drawn into the engine through that hose. Maybe enough to keep it from running unless it’s floored, which brings in maximum amount of air. Pinch the hose shut with a clamp, or plug it with a BB or piece of a nail, and see what happens then.
When I took the air cleaner off this morning I found I had disconnected the hose to the choke opener. It started up and idled smoothly immediately (with the help of the jumpstarter). It still lags when cold.
Suggest to clarify the current situation w/your truck ? Is this correct?
Start up is normal, cold and warm, idles good cold & warm, choke plate is behaving as expected on cold starts and as engine warms up, but the remaining problem is when engine is cold or warm and you step on the accel pedal quickly, engine stalls or balks like it is going to stall?
I drove yesterday. It didn’t lag or stall. I had to warm it up for a few seconds, something I hate to do. I had turned down the idle, added a can of Supertech™ motor treatment, filled the tank.
It seems that it often won’t start the first time. I check everything under the hood, find nothing wrong, then it starts fine, although I don’t think I did anything that would matter.
One theory: This could occur if the fuel level in the carb’s fuel bowl is lower than spec prior to the first attempted start. The first attempt cranks the engine which pumps more gas into the fuel bowl, so on the next cranking attempt it starts normally.
gasoline evaporates from fuel bowl. Either into the air or it moves into the evap system, more likely explanation if several days or weeks b/t use.
gasoline leaks from fuel bowl into the intake manifold, usual cause is a problem w/the carburetor or its parts
external gasoline leak, most likely from fuel bowl through faulty accel pump
Absent super-smell, you wouldn’t normally notice much if any odor from the first two, but might from the last one.
I expect its possible, but no idea how it is done w/your particular carb. On mine, while a fiddly job, fairly quick & easy. Remove the air filter ass’y , then the fuel bowl cover, 4 screws.
There’s a glass window on the carb. Gas should be about halfway up the diameter of that window. You might have to remove the air cleaner and maybe use a mirror to see. It was easy to see on my 1979 Toyota 4X4, as I recall.
No. I could crank the engine with my breaker bar to make it work. It must have gas in the bowl to start up readily, which it usually does, but I never see a level in the sight glass.