I have tried everything, checked literally everything, rebuilt and disassembled carb numerous times, set float wet and dry, etc, etc. '76 F250 4X4 360 C6 runs absolutely flawlessly once warmed-up but loads up seriously when cold. Auto choke works fine it seems but I feel that if I installed a manual choke I could control it might solve the problem. EGR, vacuum advance and everything else seems correct. Distributor works fine and in good condition, cap, rotor and plugs new. Vacuum lines correct and good. ???????

 

I know you said the choke is working, but lets make sure its set up right before we eliminate it. What is the spring set to and how wide is your pull-down?

If the choke is not the problem, I'd be looking at a slight vacuum leak under the carb or the EGR coming on before the engine is warm enough due to a faulty ported vacuum switch.

 

Thanks for the info!

 

Heat riser to the air cleaner working? If not, it could be icing up in the carb.

 

The heat riser is the thermostatically controlled flap in the air cleaner snorkel, right? If so, mine is working just fine. I just bought three remanufactured carbs, all of which I plan to return, which are susposedly correct for my '76 F250 360 4X4 to compare them and their specs to my original MC 2100 which I just rebuilt and which seems to be in excellent unworn condition. Two of the carbs are MC 2150s, pretty poorly remanufactured, with 1-9/16" throttle bores. In one of them the power valve was completely cross-threaded and screwed in anyway. The third carb is a Holley remanufactured unit, $50 cheaper than the other two (192.50) and appears to be nearly all new parts and an MC2100 with 1-11/16" throttle bores just like my original carb. It looks like a really nice unit and it comes with an excellent instruction manual. I'm going to document all of its adjustments, disassemble it, compare it to mine, adjust mine to its specs, reassemble it and return it. I have pretty much come to the conclusion that my carb is not at fault and that it's the 109000 miles on my engine and maybe the EGR valve that is giving me the trouble. The engine runs very well once it's warmed-up. One difference I noticed right off about the Holley remanufactured carb (HRC) is that the choke plate is opened wider when the pull-down plunger is held down as when the engine first starts up. The specs in my rebuild instructions state that the bottom edge of the choke plate should be open 11/64" and on the HRC it looks to be about 1/4". I tried setting my carb to about 1/4" last week in an attempt to get it to run better during warm-up but it didn't seem to help. If this HRC is set differently I'll at least try that again .

 

Wow...3 reman carbs can't be cheap.

I'm guessing that while pulling the carb off and on this much you've probably moved the EGR spacer plate around some right? Have you replaced the gasket between the spacer and the manifold? A small vacuum leak in this area can go unnoticed while the engine's warm but will surely be noticeable when the engine is warming up. You may want to spray for leaks around the carb base.

Here is some clarification on the EGR possibility if you're interested. If the EGR valve is causing trouble, it may be getting vacuum signal too "early" because of a faulty ported vacuum switch, which is supposed to block off vacuum to EGR until the coolant reaches a certain temperature. EGR coming on before the engine is warm enough was known to cause many "driveability" problems when EGR first came out. Or, the valve could be stuck open too, in which case the valve doesn't care about the vacuum signal it's getting.

 

I rechecked the prices and they were all with in $10. I'm returning them all so I'm not concerned about the cost.

I suspected an EGR malfunction so I made a plate to block it off completely and it made no difference even though I can see that it opens and closes when I operate the throttle once the engine is warm. The thermo valve works properly.

The gasket under the EGR/carb spacer plate probably should be replaced but I don't think it's actually leaking. I will check it with some WD-40 or starting fluid.