Vacuum advance dist on 2.8

[ammohead]

I have a stanadard varijet 2bbl carb with a vacuum advance distributor on my 1986 comanche's third engine a 2.8. Originally it had California emissions that have fallen off somewhere along the way. An experienced emissions tech converted it to it's current state with the first rebuilt engine that was installed in 2000. After I did the swap on the current rebuild the engine seems a bit flat on acceleration. When I put a timing light on it and adjust to 10 degrees at low idle I Don't see an advance of the timing when revving. Where on the carburator should the vacuum advance be attached? Currently it is attached to the spacer between the carb and manifold. Is there a better place, perhaps higher on the carb body?

[carnuck]

Did someone previously try converting to GM Fuel injection?

If not, then your mechanical advance should be advancing too. Also, some cheap brand ignition rotors were know for jamming the HEI advance weights. That or your distributor may be hooked up to run GM EFI and it’s Computer controls the timing through a second pigtail.

I saw some guys hook the advance to manifold vacuum which causes it to retard with the throttle and the mechanical advance counteracted it by advancing with the engine RPMs. Timing didn’t jump forward again till the throttle was let off.

This doesn’t account for CTOs (Coolant Temperature Overides) in the vacuum line that work/don’t work depending on the engine temp or if it even works right.

I run ported vacuum (hg/in rises with the throttle applied until past 3/4 throttle opening. )

 

As to where it plugs into the carb, that depends on which carb it has. You can check the ports with a vacuum gauge or even a clean hose to your tongue or finger.

 

 

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[Jeep Driver]

The vacuum port could be clogged or line clogged or cracked or split. 

[Green Mesa XJ]

I believe the timing for the automatic needs to be around 12 degrees, the California emission with the computer controlling advancing was about 10 degrees. You may just need to bump the timing up a little. Strangely my 2.8 manual transmission is supposed to be 17 degrees, maybe because it’s high altitude emissions.

If you’ve got the right distributor I’m not sure why it’s not advancing, I’ll post a vacuum diagram for the factory set up but you can hook up the vacuum line to the distributor several places.
This weekend I’m going to post the way I’ve set up the vacuum lines with a Weber carburetor for another member.




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