Hello, this is my first time posting here so please forgive me if this question is simmilar to pervious posts. I have a 1985 F250 longbed with 63K miles on it. It has the 351W engine coupled to C6 tranny and the Holley 4180 carb. My problem is the engine would not run without the choke being tied almost shut so I took the carb off and rebuilt it entirely with a rebuild kit. I made sure to remove all of the old gasket material, wash off any tarnish, and flush out all the jets and passages. The kit included new gaskets, diaphrams, o-rings, and float valves. After rebuilding the carb and reinstalling it on the engine, I adjusted the fuel level in the floats. Right now the engine starts fine but will not stay running until it is warmed up unless I keep my foot lightly on the gas. Once the engine warms up it idles well and pulls 20-21 in/hg of vacuum. With no load the engine will idle and accelerate well. When I put the truck in gear it lugs for a second and then smooths out and idles fine. My problem is when I try to give the engine gas it will accelerate briefly for a few seconds and then it wants to die. I have been messing around with the engine for a couple weeks now and have not been able to pinpoint the cause. I've looked for vacuum leaks by pulling lines off the manifold tee's one at a time and capping them to look for a difference in vacuum with no luck and have also tried the unlit propane torch approach. Out of desperation I took the carb back off, cleaned out all the passages again, and swapped the new power valve with the old one. None of this has made any difference to the running performance. If anyone could point me in the right direction as to where I should look next it would be greatly appreciated.

Thanks,
Jim

 

Here are a few things to try: 1. With engine warmed up, set the curb idle to the spec on your sticker with trans in drive. I think it should be 600 to 650 rpm. 2. Make sure the choke settings are correct. 3. The fast idle rpm adjustment may need to be increased so you don't have to keep your foot on the pedal. 4. Turn the primary mixture screws about an additional 1/4 turn out (CCW) which should help the hesitation. 5. Make sure the distributor vacuum advance is connected to the proper vacuum port and is working properly (i.e., advances with vacuum applied and doesn't leak down).

 

Thanks Piffery1, I took the carb back off, drilled out the caps over the idle mixture screws to open them up 1/4 turn, and increased the fast idle speed. Now the engine seems to be running much better when I put it in gear and step on the accelerator. Tomorrow I'll try tweaking the mixture a little better and set the curb idle and fast idle to specification. Thanks again for the advice, it was greatly appreciated.

Jim