Idle drop issues.

[1984ranger28]

Hi, I finished the duraspark conversion om 2.8 about a week ago. Got the engine running better than ever. There is a small issue with the idle however. After revving the engine and quickly releasing the throttle shaft, it dips below idle around 100 rpms for about 2 seconds, then returns to normal. It doesn't seem like it wants to die. What are some problems that could cause this? Thanks, Lucas.

 

[RonD]

What source are you using for Vacuum advance?

There are two types of Vacuum with any gasoline engine, intake vacuum and ported vacuum

Intake vacuum has high vacuum when throttle is closed, lower vacuum as throttle opens
Ported vacuum has little or no vacuum when throttle is closed, then gets higher vacuum as throttle opens

And there are two types of distributor vacuum advance, lol

Ported vacuum is found on a carburetor ABOVE the throttle plate, there will be a port
In this picture its port #5: https://www.ford-trucks.com/forums/1424779-for-anyone-who-needs-a-mc2150-vacuum-port-diagram.html

If you are already using Ported Vacuum then switch to Intake vacuum and see if that solves the problem

 

[1984ranger28]

Thanks for the response. I did have the distributor going to ported vacuum, so I swapped it to manifold. The problem didnt go away, but it did help. The idle now returns to normal in a 1/2 second to 1 second.