So I’ve been troubleshooting this for over a month - ‘56 235 in my ‘41 p/u:
Idles fine at approximately 21” vacuum until around 1200-1300RPM lowers slightly but past 1300 or so RPM the vacuum decreases significantly until nearly zero at WOT and engine begins to run poorly.I tried pouring a very small amount of gas down the carb at wot to detect any change in engine sound or rpm and there was none. Replaced spark plugs and cleaned them when they began to look black, rebuilt carb, timing seems ok, new points and condenser, new fuel pump and filter.
As of now, I’m focusing on either fuel starvation from carb or restricted exhaust. Also, on the street it runs fine as long as the RPMs stay low. It does seem to lose slightly more power at the higher throttle when at full operating temperature. Haven’t taken truck too far from the house due to the same exact symptoms every outing.
I know this topic has been addressed in older posts but nothing I’ve read has solved the problem or the remedy was never specified in the posts. TIA…
