[obnxshz]

Originally Posted by GoatRider

Depending how extensive your engine modifications were, you could have radically changed the vacuum signal that the modulator is seeing. (Also as mentioned make sure the line is still attached and not kinked.)

Some TH400 modulators are adjustable by inserting a small, flat bladed screwdriver inside the vac. port. I would experiment with that first since it is an easy fix. Sorry but I can't remember which way turning the screw does what to your modulator function.

JS

Turning it clockwise reduces vacuum signal thus raising and friming shift point. Turning counter clockwise.. well you can figure that one out...
I usually go 1 to 1 1/2 turns at a time and test to get it where I want...

I also agree with checking the vacuum source and put a gauge on it to make sute it is within specs...

Good luck!