84 w250 idle peters out... float adjustment?

[eljefino]

84 dodge w250 yard plow truck. Came with a 2 bbl Holley, replaced it with a (don't laugh) "Dromedary" Chinese Carter knock-off.

Has an automatic choke, which works well enough, and it holds a high idle. The issue is when the truck warms up enough, it won't hold a consistent idle. Just cranking up the stop screw isn't a cure, as I have to have it at 1500+ RPM to power through the "low spots."

Set, by ear, to a reasonable, or somewhat-above-reasonable idle, it gets into a funk where it idles slower and slower and just peters out. A stab at the gas pedal, hard enough to trigger the accellerator pump, brings it back. Fuel is managed pretty well, using sta-bil, winter RVP gas, and rotating new for old. It makes good power when plowing.

Thinking I had a bad fuel pump, I wired up an electric one, no difference. When I unplug the electric pump, to "run it dry" for summer storage, it stalls out in about three seconds. This is counter to my small OPE which will idle on what's in the carburetor's bowl for 20-30 seconds.

Anyone else with such a set up care to comment? Seems like my float bowl is nearly dry and could use some more fuel. There is also the possibility that it's anything else, like a vacuum leak, etc. The thing's not on the road so I really only need PCV and the brake booster, maybe I'll tackle that angle and plug off the rest of the hoses.

 

[Gyro Gearloose]

I once had a car doing the opposite and going way too rich after long periods of idle. Turned out that the needle valve was worn and the excess side play allowed it to wedge in the valve cage and lock up. Normal driving provided enough vibration to keep it moving. Its a long shot but one of those weird things you would never expect..

 

[zrxkawboy]

Sorry to say, but with a Chinese carb, who knows?

 

[wpod]

Why the new carb? Did the problem start after the carb install?

 

[Brian123]

84 dodge w250 yard plow truck. Came with a 2 bbl Holley, replaced it with a (don't laugh) "Dromedary" Chinese Carter knock-off.

Has an automatic choke, which works well enough, and it holds a high idle. The issue is when the truck warms up enough, it won't hold a consistent idle. Just cranking up the stop screw isn't a cure, as I have to have it at 1500+ RPM to power through the "low spots."

Set, by ear, to a reasonable, or somewhat-above-reasonable idle, it gets into a funk where it idles slower and slower and just peters out. A stab at the gas pedal, hard enough to trigger the accellerator pump, brings it back. Fuel is managed pretty well, using sta-bil, winter RVP gas, and rotating new for old. It makes good power when plowing.

Thinking I had a bad fuel pump, I wired up an electric one, no difference. When I unplug the electric pump, to "run it dry" for summer storage, it stalls out in about three seconds. This is counter to my small OPE which will idle on what's in the carburetor's bowl for 20-30 seconds.

Anyone else with such a set up care to comment? Seems like my float bowl is nearly dry and could use some more fuel. There is also the possibility that it's anything else, like a vacuum leak, etc. The thing's not on the road so I really only need PCV and the brake booster, maybe I'll tackle that angle and plug off the rest of the hoses.

I will not laugh, but how much would it have been for a new 2 bbl Holley from the good old USA versus what you bought?

 

[supton]

Watched a vid where they installed an O2 sensor with a hole saw, clamp and metal zip ties, but no welding. Don’t think it’s worth spending a lot on, but would rigging up one help? less guessing about rich vs lean.

At its age, any chance gas tank crud got through the filter and into something? or a cracked vacuum line. Does this have weights in the distributor for advance?

But it sounds like a low float level. New enough that I would think you could reuse the gasket.

 

[eljefino]

Why the new carb? Did the problem start after the carb install?

Great question, because the truck was somewhat of a bear under the old one too! The replacement was five years ago, FWIW, but I'm just now bored enough to try to get this running better. I did find some roughness in the auto-choke operation that I cleared up, sticky linkage.

Question remains, what about three seconds worth of gas being in the bowl at any given moment?

 

[mk378]

Vacuum advance is important for idling. Actually the concept is to retard the timing while idling so the rpm will stay down without having to restrict the air to practically nothing, which would make for a very touchy adjustment. Put a timing light on to see if the system is working. It should be at base time while idling then advance sharply as soon as the throttle is moved off the stop.

 

[eljefino]

Thanks, will do. The vacuum advance is run by a dumb analog computer with 1/8 plastic lines going everywhere. You've convinced me to break out the vacuum gauge.

I got the carb apart and made what I felt was the smallest adjustment to get more fuel in there. There is a slot in the accellerator pump well, does anyone know if fuel is supposed to get in that slot or not?

 

[eljefino]

Well I fiddled with it, ripped out a huge amount of vacuum line. That "computer" was an amplifier that took direct intake vacuum. Got the distributor directly connected to ported vacuum. The carb bowl vent still goes to the charcoal canister... and that's about all! It runs for half a minute now when I unplug the fuel pump, idles forever, calling it a success.