AMC V8 Idle issues

The vacuum advance can on your new dist is adjustable (so sez the manuf.) using a small allen tool inserted in the front of the vacuum can via the vacuum inlet tube.

 

Wait couch, thanks for that but where did you find that info, I looked everywhere even contacting them and I got nothing. Any ideas on how much either way or is it just trail and error. Also what size allen key is it?

 

Tell you what. Cap the two vacuum ports (one on the carb, and one on the manifold) and set the initial timing at idle to 10 degrees before TDC and just use the weights in the dizzy to do the advance. Then you won't have to worry about it.

And remember that along in there somewhere you had a double can that did both retard and advance as another attempt at emissions control.

Plus what are the laws about emissions in Ireland? Do they cover all vehicles back to 1966 or do they only go back 10 years or 20 years?
Bet you have to keep all that stuff on the engine to pass.

 

Just looked the year thing up. Your Jeep was built before 1980, and probably registered before 1980, and is therefore exempt. Which makes things a lot easier.

 

This may help with setting your timing. you can google this, " Timiing and Vacuum Advance 101" by John Kinckley, or "How to set your timing for peak performance" by lars grimsrud. They are retired GM engineers that designed these systems back in the day. There are articles on points ignition and electronic. Awsome information but hard to grasp whats taking place, I read it several times before I fully understood what was going on.

 

Thanks guys for your responses
I had another look at this today, I was right 25* vac advance at idle, so I disconnected the vac line and plugged it. Timed the engine to 14* initial and then ran it up to 2900 RPM to see what total I got which was 30*. So I'm getting 16* mechanical advance.
So after that I set about fiddling with the vac canister, I tried adjusting it (both ways) to see what change it made on the amount of advance. I got 20* one way and 25* the other way so still no where near where it should be. I opened up the dizzy to see what was going on and saw the vac advance lever and its adjustment. I then tried turning the canister adjustment and found then only thing that changed was the amount of vacuum required to operate the lever, One way softened it the other hardened it. I had seen on the interweb that you can buy/make a limiting plate and attach this to the dizzy. So that's what I did, it was very much trial and error on the length of the plate but eventually I got to 13* advance. (I had 8* on an early try and took 0.5mm off and went to 13* so very sensitive).

Here is a quick snap of the plate



So at the mo these are the figures:

14* initial
30* total (2900 RPM)
16* Mechanical
13* Vac advance at idle

The Jeep seems to run great, haven't been off roading but seems smooth and pulls happily, question is I'm still off the recommended 32-36* total, but if I advance the initial any more I'll be advancing the Vac too. Ideas?

 

Your vac advance should be limited by the limiting plate, so it cant go higher, you have full advance at idle running manifold vac so it cant go any higher with the limiting plate there. IDK, if its running great you may just want to leave it there, you can always try 32 or 34 (by taking your initial to 16*. There and above the starter may want to kickback at start up, just take you initial back to 14* if that happens) and see how it runs and go back if you don't like it. The hard part is done, you have the vac advance dialed in, now you can find a initial timing setting that the motor likes and as long as your initial and total with no vac stays below 36 you will be fine. Add your vac advance to the total and that will be your total for cruise and light throttle. I think you have it nailed, just fine tune it with playing with the initial.

 

Thanks for that, is it ok to raise the initial by 2* effectively increasing total to 32* but the idle timing would be 29* (16* initial + 13* vac) or do I need to back off the vac to say 10* by making a new plate.

 

Yes that is fine raising it. your 29* at idle is initial plus full vac advance. The starter usually starts to kickback with too high of a initial, yours is 14. you see 29 at idle because you have full vac advance on top of your initial. When you raise the initial you will also raise the total by the same amount but the vac advance should stay the same now that it is set

 

Ok. Stick your Vac gauge on there and tell us the reading at idle.
And what is your idle speed set at?

 

I won't be back at the garage till Friday so I'll let you know as soon as I can. From memory idle RPM was 750