FMX Transmission Stutter

[RGunter]

Hi all,
I have a 71 Mach 1 with a 351c and an FMX transmission.
I recently installed a Pertronix Ignitor and a new Pertronix coil. At the same time I installed a phenolic carb spacer. This made my cranking much better. But it also advanced my timing and was idling too fast. I read where installing the Pertronix unit could cause that, so I backed the timing down to 12 degrees and set the idle about 800 RPM. The car ran good and seemed happy with that.
But when I went to drive it, the transmission would hardly engage. It was sluggish and “stuttering”. If I pushed the accelerator and revved it up some it seemed to catch.
My question is; could me backing the idle down be causing too low of vacuum to the transmission? I might have thought it was a vacuum leak, but it was perfectly fine until I backed the timing and idle down.
I am a little puzzled. Does anybody have any thoughts?
I should also say the transmission was rebuilt 12 months ago and has a new vacuum modulator.

 

[Spike Morelli]

Why not check your engine's vacuum with a guage? That will tell you if vacuum is too low.

 

[vintageman]

Agee with Spike above, check the vacuum with a gauge. Also, by any chance have you checked your trans fluid level, if it is too low, it will feel like you have to rev the engine up to really get moving.

Good luck
Tom

 

[RGunter]

Why not check your engine's vacuum with a guage? That will tell you if vacuum is too low.

I will do that. I have a gauge. How many inches should it be pulling? 12 to 15??

 

[RGunter]

Agee with Spike above, check the vacuum with a gauge. Also, by any chance have you checked your trans fluid level, if it is too low, it will feel like you have to rev the engine up to really get moving.

Good luck
Tom

I’ve checked it and it shows full. But now that you make me think of it, I wonder if it’s the right dip stick. It bottoms out and doesn’t completely sit down on the tube at the top. Perhaps I’m getting a bad reading? The stick seems it
May be too long. Thanks for reminding me of that.

 

[Hemikiller]

Take a look on the stick, it should have an engineering number stamped into it. Post a pic if you can.

 

[RGunter]

Take a look on the stick, it should have an engineering number stamped into it. Post a pic if you can.

Here is the stick. And I checked the vacuum on the manifold port on the carb. It showed 16 inches of vacuum. That’s where the transmission vacuum is pulling from.

 

[Bentworker]

Carb spacer may have tweaked your kickdown geometry

 

[California 72]

The kickdown linkage is a good suggestion to check. The other thing, when you installed your spacer, I'm guessing you removed all the vacuum lines at that time so, did you reinstall them accordingly or maybe crossed a couple and now have them in the wrong ports? It's easy enough to do, even with this project but please don't ask me what goes where since my car is in pieces and I'm unable to go take a quick pic.
Come to think of it, I'm going to have my own fight remembering where everything went so when, and that's a big when, I get things back together, this topic will definitely help since most if not all the gang posting here currently answering you will probably bring one up for you to see. I think Hemikiller and or Spike has one readily available.