Ignition timing keeps changing

[GoClimbAMountain]

I'm restoring my 80 CJ5 . So far, rebuilt my AMC 258 i6 / 4.2l , new Weber carb, new electronic ignition, new distributor. All vacuum lines hooked up.

Here's my problem. I can get the timing set just right and turn it off, back on, let it heat up, cool down and the timing stays. However, next morning i can start it and the timing will be totally off. I have to readjust it until the next morning when it will be off the other way. This has happened most mornings. Is this a distributor problem? Maybe the vacuum advance mechanism malfunctioning? It can have something like a 20+ degree shift, either way.

I'm chasing it but can't zero in on it.

 

[mtnwhlr]

I think it's the dissy, do you still have the old one if so put it in and see if it still does it.

 

[Torxhead]

You could try plugging up the vacuum advance line and run your previous test just to rule it out. It very well could be the mechanical advance in the distributor also.

 

[jp360cj]

What ignition are you running?

Does it always shift the same way (always advanced or retarded), or is it seemingly random? I'm wondering if the vacuum or mechanical advance is sticking.


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[Lumpy Grits]

with all of the above.
Also-Make sure the distributor's hold down clamp does in fact not let the dizzy move.
LG

 

[Torxhead]

with all of the above.
Also-Make sure the distributor's hold down clamp does in fact not let the dizzy move.
LG

Yeah, like too long of a distributor hold down bolt too prevent it from locking in position.

 

[GoClimbAMountain]

Thanks to all for the help so far. I'm beginning to think it is my distributer. I got inside and shifted the vacuum diaphram on the mechanical vacuum advance and made sure my cap was right and that i had no leaks. One other variable in all this may also be my timing light. I'm not convinced that the dial for timing shift on it is good. Not sure why its there anyway since you have the graduated marks near the pulley.

I'll keep you posted as i discover more.

Thanks again to all!

 

[GoClimbAMountain]

OK, I'm back. I haven't been able to try a new distributor but still diagnosing but have a few questions. I seem to be finding contradictory information online.
1. When setting the timing, do I disconnect the vacuum advance on the distributor?
2. One thing that I read said that you shouldn't see much, if any, vacuum on the carb at idle speed. However, it appears that I have quite a bit of vacuum on the carb so that the timing is totally different (about 20-30 degrees) between the vacuum connected and not connected.
3. When I set the timing with the vacuum advance connected, I get significant blowback out the carb when the engine is stopped. This goes away when I set the timing without vacuum advance.
4. But, if I set the timing without vacuum advance connected, then connect it back up, the timing shifts from about 5 BTDC to around 30 BTDC. Seems like a very large shift. The engine doesn't idle smoothly in this state.

What am I missing or doing wrong? Any input is helpful.

Thanks.

 

[mtnwhlr]

Yes you should set your timing with the vac unhooked and plugged.
There are two kinds of vac, ported and non-ported. You should be running ported vac. Ported vac will read 0 at idle and should run off the upper part of your carb.

 

[GoClimbAMountain]

Showing my ignorance here... there is a port below the electronic choke that always has vacuum. There is another that is connected to the pcv valve in the valve cover. Which is which?

 

[mtnwhlr]

There should be one on the upper part of the carb. It's the only place you will find ported vac.

 

[GoClimbAMountain]

I see 4 ports on my 32/36 weber:
1. A 3/16 port below the electronic choke next to the idle mix screw. It always has vacuum
2. A 3/8 port into the car to manifold adapter. It goes to the pcv valveand distributor for now.
3. A 3/8 port for, i think, the vent for bowl going to the cannister.
4. Port into the breather. Going to the rear of the valve cover

Unless one of these is it I dont see a port above the throttle plates. Perhaps Im missing something? Which makes the most sense to use?

Sorry to be so slow.

 

[mtnwhlr]

It needs to be above the throttle plates to be ported. I have never had a weber hopefully someone with one will chime in. I like the Motorcraft carbs.