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I have an annoying issue with my 98. It over fuels bad at a certain tiny spot in the throttle but only on takeoff. Truck is a 5 speed with 215 pump with a home cut 100 plate. I have the plate slid halfway forward and if I back the smoke screw out anymore it will fall off. The star wheel has been adjusted slightly and the housing itself is about centered. Truck runs really clean up top and down low, except for this small spot in the throttle on take off. I usually ease into the throttle and miss the spot but once or twice a week ill accidentally find it and it belches thick black smoke. I have a needle valve at the afc on the boost reference line. I also have PDD Bosch 5x.012 injectors set at 305 bar and like I said before, truck runs real good and clean every other part of driving. Ill see if I can get a couple videos this weekend.

Since it's all mechanical,  maybe something is sticking internally. Make sure obvious things are free and able to move around if they need to 

I don’t k ow enough about it to know what I’m doing. I’ll just keep driving it the way I have been and not worry about it

Boost leak on the AFC side maybe?

I have tested for leaks but have not found any

 are you sure you're not lugging the engine down a little and then applying throttle?  On mine, below 600 RPM the governor arm will slide under the AFC foot and allow full fuel, and will get stuck there for a second until the RPM's rise.  Nothing unsafe or scary about it but it does belch out smoke unintentionally.

I dont believe it drops that low but I think I actually may have figured it out. The truck has also done something weird for a while, when the engine is cold and I shift it would bounce up in rpm when it hit idle speed, like I touched the throttle. I thought it was the new injectors since it started directly after install. I adjusted the 4k gsk yesterday and I didnt see any smoke today and no sticking throttle. Nice surprise was that the bounce at cold shift it gone too, truck has more power now as well. Im not sure where I had the gsk set at before but I put them 6 clicks total each.