Hi All. One of my toys is a '79 class c motorhome built on a e350 cutaway chassis with the original 460 4 bbl and c 6 tranny. It is all original and only has 46k miles. It is in excellent condition. It used to have a slight hesitation when accelerating from a dead stop so I rebuilt the carb, changed the fuel filters, cleaned the gas tanks, and replaced the rubber fuel lines. That seemed to resolve the hesitation. It has the stock mechanical fuel pump as well as a Carter elec. fuel pump. It starts on the first crank, runs exceptionally smooth, idles smoothly but after it is driven around 3-4 miles, it will suddenly drop in RPMs while idling and and act like it wants to stall or die. If I give it some gas, it will then run ok. It does this regardless if its 90 degrees outside or 9 degrees. It has the appropriate fuel psi according to stock specs. I plan on changing the spark plugs, spark wires, coil, ignition module, and distributor as it can probably stand a change. If anyone has experienced this or has any ideas, please let me know as it would be greatly appreciated. Thanks for your time!

 

Sounds like it is trying to flood, maybe? What about a choke issue or maybe secondaries opening. These are hard to troubleshoot.
jim

 

Changing the items you mentioned is good maintenance I would do anyway, especially considering age. I assume you mean distributor cap. I would not change the distributor unless it had play in the shaft or rust on the plates. It does sound like a fuel system issue. Is there old stale fuel in the tank? Also, was the float changed changed during the carb rebuild? Not a bad idea. If the float sticks up, it could starve for fuel. Hitting the gas would not improve with a stuck float unless the accelerator pump squirt of gas is the cure or the linkage jiggling the carb frees the float a bit (that is a stretch).

 

You know Jim, I too thought that perhaps it's getting too much fuel but I don't know exactly why I suspect that. It's not vapor lock, that much I'm pretty sure of. I did change the choke pull off as it wasn't operating but that didn't seem to make a difference. The float was changed during the rebuild. I don't think it's the ignition module as they usually display a different symptom when going bad but I guess I'll see what happens after I do the maintenance that I mentioned. Thanks for your input!

 

Sorry, I did mean distributor cap. I cleaned out both gas tanks this summer and they weren't dirty at all but I cleaned them out anyway. No stale fuel in the tanks and I only use high quality fuel and keep it fresh. Like I said, I'm going to do some maintenance and then reassess. It almost mimics an electrical problem so we'll see with the new wires and ignition module. I might also put a new painless wiring harness in, just the wiring for the distributor to the module as it is the original wiring. Any other ideas let me know and thanks for your input!

 

Is there an EGR on this one? If that hangs open at idle, it usually stumbles and dies. One thing to try is (carefully) squirting some fuel down the throat to determine if it is starving or flooding. That will at least give you a direction for troubleshooting. It seems that 3 or 4 miles of driving to warm up makes it temperature related.
jim

 

When you changed the choke pull off did you set the proper gap on the choke plate?
Once the engine starts the choke pull off is supposed to open the choke a specified amount to keep it running until the electric choke opens it on up. I don't know about the 460 4bbl but my 2150 2bbl choke gap was set using a 3/16 drill bit..
Thinking though that would only make it flood out before it warms up.. If the electric choke has gone bad or out of adjustment and not opening up fast enough, that might do it...