Been running my Fitech install about a month and it runs great but I noticed my MPG went down compared to carb.
I checked the ported vacuum and it doesn't give any vacuum until 3500rpm so this is my problem. With my 518 tranny cruising RPM is 2000-2500.

FiTechs only solution is to use manifold vacuum, sounded like a known problem.
With my initial set to 15, won't this cause hard starts?

Any other ideas?

Why would running the advance off manifold vacuum cause hard starts? You still only have the initial 15° while cranking.

You might find your problem isn't starting, but trying to maintain a stable idle speed.

Always read you never want to run manifold vacuum for the advance.
I guess there's no option in this case. We'll see how it performs with the change.

Interesting, as advertised, the vacuum advance definitely improves the gas mileage. The loss of the 15 degrees from no vacuum advance cost me about 3-4 mpg.

Ported vacuum should show up just after the throttle blades are opened. If it's not showing up until higher throttle openings, it could be related.

I'm assuming your timing is being ran by the distributor/vac advance, and not the Fitech unit?

As long as your idle vacuum (in D if automatic) is a few points above where the vac advance drops out, you can run it off manifold just fine.

ie, idles in gear at 13", make sure the can is 'all in' by 10ish.

You just don't want it to idle near where the can starts to move, otherwise it will really start to hunt as the can backs off, which changes the timing, which changes the idle speed, which changes the vacuum, which changes the timing

The tipping point on the vacuum advance can is adjustable on stock distributors.

Not understanding,
With the distributor hooked up to manifold vacuum now, all the advance is in at idle.
So the way it is now, the only added advance after idle is the centrifugal weights force limited by the springs

At high load (very low vacuum), the vac advance drops out. So, under load when you floor it, it goes away and you're left with the initial + mechanical, limiting total advance to 30ish degrees to avoid pinging.

At idle and cruising, you should have 10"+ of vacuum, so the vac advance is adding to the initial + mechanical, just like ported does. Giving you 45ish total, cleaning up the burn and improving MPG.

Ported just has zero vacuum at idle, but otherwise works the same when you're above idle.

if you set the initial to 15 on manifold when running I could see that it automatically being way retarded from that when starting (from no vac adv) could cause very hard starting. Maybe there is enough cranking vacuum to activate it, I never thought about that. You might Google it or call FiTech or Don at FBO (he is a manifold afficionado) As they've for sure dealt with this. holler how it goes.

Lot's of folks advocate using manifold vacuum. All my cars run noticeably better with manifold vacuum including my FI Tech car.

No other choice at this point,
After I connected the manifold vacuum, it idled rough and had a serious backfire with I blipped the throttle.
I'm hoping the ECU just needs to relearn with the new set-up.

what was the initial when you connected it to manifold and is the rotor phasing OK?