Rebuilt a 78 f250 351m, manual trans. Did a complete rebuild, bored .30, new cam, rebuilt heads and put new aluminum intake and holley 4160 carb. Engine runs good with good power, have the timing set around 10 degrees. Only issue im having is it hesitates and stumbles when shifting into the next gear. Detailed explanation is while accelerating, push the clutch in to shift into next gear, and when your letting up on the clutch and next gear grabs, engine stumbles. Almost sounds like it cuts out for a second until you hit the gas. It seems if you feather the throttle while in the shifting process it runs and sounds normal. Does anyone have any ideas on what this might be? checked the float levels, accelerator pump is adjusted correctly. When i get my vacuum gauge from work tomorrow ill check the idle screws again. Anyone had any issues with the 4160 carb? right out of the box the power valve had a leak due to it being assembled with 2 gaskets stacked on top of each other.

 

this is the windsor family forum.

set the timing back down to 8* and perhaps rebuild the carb.

 

I wouldn't retard the timing, I'd advance it a few more degrees. Retarding it will just magnify the problem. I would also check the sealing of the intake gaskets to see if you possibly have a vacuum leak. Spray carb cleaner as it's running and see if the idle speed reacts to the carb cleaner.

 

Might also look at the vacuum advance pod on the distributor to make sure it's working. Remove the cap and pop the end of the hose off the source it's connected to and while sucking on the hose, look at the breaker plate inside the distributor body to see if it's moving.