Timing with vacuum gage ?s

[Collin the Hen]

Hey guys,
Are there any tips on timing with a vacuum gage? I know it's not dead on, but it's got to be better than my timing as of now. I might just go for it and dive into my engine compartment today... wish me luck!
P.S. ANY advise is much appreciated!

 

[mud4feet]

You've probably posted it before, but..........what year/model Jeep do you have???? Helps a bunch trying to figure things out. I need a computer genius to make any timing adjustments on my '03.

Perhaps list your year/model in your profile?? Or in your sig????

 

[Dace]

Vacuum timing is pretty accurate providing your timing components are not worn. A slow flucuation of the gauge could indicate an overly rich air/fuel mixture or worn chain, distributor drive and gears. No amount of tweaking will fix this. Of course I am assuming your Jeep is distributed and carburated.

 

[dave123]

What you do is set the timing to the highest steady vacuum at idle. Although this should be close to correct, I would still prefer to do it with a timing light.

This works on pre-computer engines, I would not try it with a newer engine.

 

[Collin the Hen]

Thanks for the advise! By the way, it's an 84 CJ7 with a 258, Motorcraft 2100, and the Nutter Bypass. The vacuum is steady at 4 Hg upon idle and jumps up when the throttle is opened and drops very quickly when the throttle is shut. It misses pretty bad but starts to clear up the higher the rpm. I've sprayed the manifold and around the carb to make sure there aren't any leaks; nothing happened. So I'm pretty much set on either the timing or perhaps the A/F mixture.
Two of the main Q's.
1. The vacuum is going straight from the vacuum advance to the carb. Is that ok?
2. I'm wondering if my advance is bad. Is there any way to diagnose a bad advance?

 

[dave123]

check this out:
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as for your questions, vacuum advance comes from the base of the carb. To diagnose bad advance, use a timing light and see if it goes up when you hit the throttle.

 

[Dace]

4" of vac at idle is awfully low. Where did you connect the gauge? It almost looks as if your reading ported vacuum. Depending on engine wear you should have at least 15 " vacuum at idle. 18-20' is optimal.

 

[Collin the Hen]

Yeah, I was putting my gage in the carburetor port. I plugged it in the manifold port and it read 17 Hg. I then advanced the time and it ran a lot smoother, and it jumped up to 21 Hg. The next day, though, It was as rough as before yet still at 19 to 20 Hg, so I'm just going to have to wait till my timing light comes. I'm debating on spending $90 to buy a TFI conversion for the distributor, because I'm thinking my plugs are a little too tired from the suspended retarded timing.
Main Q.
Should the timing be altered with the larger Motorcraft 2100?