86 300/6
Went through drive through. While waiting at the window and in neutral touching brake only the idle kind of bogged down and got lopey then a few seconds later it increased idle speed and smoothed out. Then back to lopey bogged and so on.

Havent had time to set and think about possible causes other than maybe a vac leak. What do yall think?

 

Oh when i left it drove fine. Just happens setting still.

 

I would tweak the idle mixture screw(s) a little bit. Make sure you tweak them when it's doing it's "thing" which would probably be when it's fully warmed up and has been driven a little bit correct?

 

If I remember, you still have the feedback carburetor. Adjusting idle mixture on those is interesting to say the least. It almost sounds like it may be heat soaking and forcing fuel past the needle and seat. The Carter YF is real sensitive to fuel pressure, we used to put pressure regulators on the AMC Pacers to solve a terrible hot start problem when they first came out.

 

Yes feedback carb. Yes fully warmed.
Its a new problem. Nothing has been changed in a good while.

Ill also add that a couple times recently it cranked a little longer to catch when it was warm and parked facing uphill on a 8% or so grade. I could smell fuel like it was borderline flooding.

 

I'd like to add that when I press my brake pedal, my idle changes slightly and goes back up to normal as well. It's not a slow thing, it's moderately fast. It drops down, then picks right back up again.

It's also a brand new brake booster, doesn't leak or anything. You can come out hours later and still have a little vacuum assist. It doesn't whistle, and the booster effect of it works really nice to help you out when you need to get on the brakes. It's definitely not sluggish as far as how it works.

I've just assumed it's the nature of the beast with these old trucks.