I'm having a couple problems with my 67 f100 ranger w/ the 300 i6. Just started happening recently. When cruising at constant throttle position, the truck will buck randomly. It feels like your blipping the throttle. Also, the truck is randomly having a hard time holding idle. It will sputter slower and slower and eventually stall. A few cranks will start it back up but it's pretty rough. I've tried adjusting the idle screw, but it doesn't seem to help. For example, when the truck seems to be idling low, I'll adjust the idle screw to speed it up a bit. After driving for awhile however, the idle will become much higher than what I thought I set it at. I'll then adjust it down. Again, after a while, it will then seem like it's idling too low and stall, etc etc.

I'm suspecting a very rich running engine, because I can smell gas pretty strongly, and at one point I looked at the carb and saw fluid covering the outside of the carb which I'm pretty sure was gas.

What I've done in the past couple of weeks:
- changed oil
- replaced oil in the oil bath air filter
- sprayed carb cleaner in and around the carb
- played with the air/fuel and idle screws (which way do I turn to lean out the air/fuel mixture?)

 

Sounds to me like its time to rebuild the carb. Also, check to see if the tank has a lot of rust inside. Small rust particals can flow past the filter, and cause the needle to not seal to the seat. This happened to me before.

Nathan