Edit: Jon always says it is never the carb, so someone tell me it isn't that carb.
We were getting the truck running today and ran into an odd issue.
The engine was cold (35°F air temp), we pulled the choke, turned the key, and it cranked and started fine.
After letting it sit and idle for a bit (90 sec?) it started running rough, so I pushed the choke in and it smoothed out. We let it sit and idle for a couple minutes while checking other things and it idled fine.
When we tried to rev it up in neutral, the throttle gets to about 1/2 and it starts hissing loudly (from the throat) and stumbles and tries to die. Letting off the throttle, it smooths out and idles just fine. The throttle position that it stumbles and dies is very consistent.
If I pull the choke out about 1/3, it still idles fine and will rev as high as you want with no noise or stumbling.
My first thought is a small vacuum leak causing a lean condition at rpm and a bit of choke is enough to richen it up. I would not expect that to get worse at higher rpm though.
I didn't have time to get the propane torch out today, so I figured I would ask if I was totally off base on this. I would order a kit from Carbking, but I can't find any tag or numbers on it.
