3E Weber Swap - Optimal Timing/Advance?

[noahthefrog]

I've just done a weber swap to a 32/36 on my 89 Tercel EZ (3E-Federal) and am having some timing issues that exceed my understanding of how engine timing and vacuum advance works... Any insight or solution would be appreciated. Please forgive the excessive detail below - I figure too much info is better than not enough.

Here's the details of the manner things are currently connected for reference:
-Using stock square "hat" type filter assembly that came with the Weber
-EGR is connected to the Weber's EGR port and the EGR valve has been tested and cleaned and works.
-Inner vacuum advance diaphragm (nearest distributor itself) is connected to intake manifold
-Outer vacuum advance is connected to the ported advance on the Weber
-PCV is split into two smaller hoses with a T-connector and goes into the same cluster of intake manifold vacuum ports (the group of three ports on the round connector near the fuel pump). Will be reinstalling original heat-riser/PCV connector once my gaskets arrive.
-valve cover breather port and charcoal canister connected to air cleaner
-"Air suction" system (for catalytic converter) has it's own breather filter separate from air cleaner.
-Redline fuel pressure regulator installed and set to between 2-2.25PSI
-New NGK spark plugs, wires & distributor cap, rotor button, battery.
-Fuel/air mixture is ideal or very close - tested using voltmeter and O2 sensor under load and idle per Haynes manual.
-currently running 89 octane fuel with minimal issues. Car runs like crap on premium gas - haven't tried 87 octane sine I replaced the carb. With OEM carb I had to use at least 89 octane or I would get no power for hills.
-Timing is set per Totota specs (took it to a shop to verify this years ago)

Everything works well enough to drive and is better than the OEM carb, but not like it should. Here's the problems:
-sometimes stutters or hesitates when going uphill at steady speed at about half-throttle in any gear/RPM. I live in the mountains, so this is like 90% of the driving I do and the biggest problem.
-Hesitates sometimes when taking off quickly at a stoplight - acts like it wants to stall, then takes off like it should. Happens worse when engine is cold (normal, i think) but also happens when warmed up sometimes.
-Everything works excellent at full throttle. Idle wavers a little, but is ok.
-Disabling EGR has little or no effect on this, so I don't think it's related.

My clue that this is timing or vacuum advance related is that I had hooked up a check valve to supply constant vacuum to the outer distributor advance by mistake (mistook it for a vacuum delay valve). Effectively, this gave maximum vacuum advance constantly. This caused the car to run perfectly except at idle, which jumped from 800RPM to 1100RPM. I get no pinging at idle with the configuration, but can't tell if it's pinging under throttle while driving. This makes me suspect my timing is at fault since the car runs better with this obviously incorrect setup.

My Questions:
Should I just advance the base timing by adjusting the distributor's base setting?
Is there a way to amplify the vacuum coming from the weber's ported advance to make it advance timing more (ie by supplying extra vacuum) when it kicks in and is that advisable?
I know premium gas isn't required, but why would it make it run worse?
If it's not the timing, is there anything else that could be causing this?

Any ideas or suggestions?

[96paseo]

As far as I know, the vacuum advance is only for helping the engine start easier. Once the vacuum reachs a certain level, the ignition timing will be determined by the distributor positon. Since its been a few years, you may want to check teh timing again with a light. The correct timing is 3 degrees BTDC. The lines to the vacuum advance should be disconnected and plugged with golf tees before setting the timing.

[noahthefrog]

From what I've read...
I'm pretty sure the vacuum advance is to adjust timing on-the-fly when the gas pedal is pressed, but engine RPMs aren't rising. RPM based timing adjustments are made by centrifugal force inside the distributor itself and that part seems to be ok as I don't have any RPM-dependent problems. It's supposed to advance the timing above idle and below full throttle in a progressive way - more advance the more I press on the gas pedal until it's floored, and then it's supposed to stop vacuum advancing.

It all works fine except when I'm at part-throttle when it should be vacuum advancing and I think it just isn't advancing enough. I checked to make sure the weber is creating vacuum on it's vacuum advance port at half-throttle and that the vacuum advance mechanism diaphragm on the distributor does hold vacuum.

Checking the timing again is probably a good idea- I've had bad luck with repair shops before and they may have just said "yeah the timing is fine" and not actually checked. Going to try some regular 87 octane gas and see if maybe it just can't handle higher octane gas and then try checking the timing myself.

All that aside, I can't be absolutely sure it is the timing or vacuum advance and not something else.

Could the computer be interfering somehow?
Anyone else had a problem like this after a Weber swap?

[96paseo]

From what I've read...
I'm pretty sure the vacuum advance is to adjust timing on-the-fly when the gas pedal is pressed, but engine RPMs aren't rising. RPM based timing adjustments are made by centrifugal force inside the distributor itself and that part seems to be ok as I don't have any RPM-dependent problems. It's supposed to advance the timing above idle and below full throttle in a progressive way - more advance the more I press on the gas pedal until it's floored, and then it's supposed to stop vacuum advancing

.

With a timing light you should be able to tell whether the advance is working correctly or not. The vacuum advance should reduce the ignition timing as RPM increases with the ignition timing being at its highest at startup and idle. You should be able to see this by increasing the RPM while firing the light. Your timing should come back closer to 3 degrees as you go up in RPM. But definitely get the mechanical timing set correctly first. Do your vacuum lines go to a TSS before going into the manifold and carb body?

[noahthefrog]

Thanks for the info 96paseo. This engine timing stuff is very confusing to me.

I took another look at the advance module and the inner one is totally caked with sludge thick enough it shredded the paper towel I was wiping it off with. I hooked up a check valve like I accidentally did to the outer diaphragm, and it had no effect on how the car ran. I think the inner advance's linkage is stuck and that would explain everything as the advance would always be a little less than it's supposed to be. Going to give it a thorough cleaning and see what happens...

[noahthefrog]

Turns out all of the vacuum advance linkage is internal and protected from the sludge. I finally figured it out, though.

The PCV hose was taking all of the vacuum from the cluster of ports I was using on the manifold for the vacuum advance and causing a dip in vacuum to the advance module. I hooked up the PCV elsewhere and the problem is gone. Hooray!

[96paseo]

Nice. Its been a while since I had to think about a carb'd engine. Last one i worked on was a '78 Corolla.