AMC 360 Timing and 727 Trans Shifting

[JohnIL]

Hey Fellas,
This is really a continuation of a previous thread, but I have new questions. So, I thought a new thread was in order.

It you want to take a look for history's sake, here's the original thread:

http://www.ifsja.org/forums/vb/showthread.php?t=75329

Here's where I am:

-1988 Grand Wagoneer
-Fresh ATK Reman AMC 360
-Original 727 transmission
-Holley 80457 4bbl carb and Edelbrock Performer intake from original 360
-Plenty of power
-20in. of vacuum at idle - 18in. of vacuum at 60mph (2500rpm)
-Really bad fuel mileage. The old engine got 12mpg. The new engine gets 8mpg

So, last night, I set the timing again in an attempt at better mileage. I previously thought it was set at 15 degrees. It turns out that it was actually set at 10 degrees. I was looking at the wrong notch on the timing tab. So, I set the timing to roughly 12 degrees on the advise of GWChris (Thanks Chris!). When I reconnected the vacuum advance to manifold vacuum, I had waaay too much advance at idle and the engine died. I don't have time before this weekend's camping trip to fiddle with adjusting the vacuum advance, so I moved it from manifold vacuum to ported vacuum to eliminate the extra advance at idle. That fixed the idle. But, I think the idle mixture is set too rich, which makes it tough to start when the engine is warm. When I took the Jeep for a test drive, it ran well, with no pinging. But, It felt like is was down a little on power. Not enough to worry about, if it improves economy, but worth mentioning. The really strange part was that after advancing the base timing to 12 degrees and moving the vacuum advance to ported vacuum, suddenly, the transmission shifts smoother than it did before. Before the engine swap, the transmission was very smooth. After the engine swap, it shifted much more positively (harsher shifts). I assumed that this was related to the way that the shop adjusted the kickdown cable, but now I'm not so sure.

Now for my questions. First, should I expect any improvement in fuel economy with these changes? Second, does the change in transmission shift behavior make any sense? Are the shift points affected by ignition timing? Are the shift points affected by vacuum?

As alway, thanks for any wisdom you guys can share.

John

[710 Burner]

Well since the 727 is regulated by the accel. linkage, the only explanation that makes sense to me is that your driveability changed in such a way as to be pulling (or not) on the linkage. Ergo, the linkage may not be adjusted correctly to begin with. It should not die with manifold vacuum connected. I ran mine like that for awhile, but I think you will find every vacuum contraption on yer motor is leaking if its like mine.