Ignition Timing Question

[Tio Pancho]

Ok rookie question here. 1977 Cherokee Chief with 360, 4 bbl. with an HEI distributor. Engine is freshly rebuilt and starts fine. No real issues there. But I need to break in the cam. My question is with the timing. I set the initial at about 5*btc with the vacuum line disconnected. But when I connect the vacuum line back up it jumps to about 15*. I believe the timing should remain at 5* after connecting the line and only advance when the throttle is applied.
What am i missing here and how do I address this? Is this done with the allen wrench inside the vacuum advance canister?

Thank you in advance.

[Tio Pancho]

Accidental double post. Mods please delete this one.
Thank you.

[will e]

Your distributor is working perfectly. The timing should increase at idle with the vacuum connected to manifold vacuum. The vacuum advance also operates at cruise and adds to the centrifugal advance. As soon as a load is placed on the engine the manifold vacuum will drop to a level below where the vacuum advance module activates. It happens very quickly.

Now, how much advance and at what vacuum will depend on the distributor and the advance cannister. Some are adjustable with an allen wrench. This typically adjust the amount of vacuum advance.

[Tio Pancho]

Your distributor is working perfectly. The timing should increase at idle with the vacuum connected to manifold vacuum. The vacuum advance also operates at cruise and adds to the centrifugal advance. As soon as a load is placed on the engine the manifold vacuum will drop to a level below where the vacuum advance module activates. It happens very quickly.

Now, how much advance and at what vacuum will depend on the distributor and the advance cannister. Some are adjustable with an allen wrench. This typically adjust the amount of vacuum advance.

Thank you Will E. I was having trouble wrapping my head around this. Much appreciated.

[Srdayflyer]

at idle the timing with vacuum should be 15 degrees, at 2000 rpm timing runs about 20-25 degrees, and at WOT wide open throttle timing runs 32-35 degrees just and fyi

[Tio Pancho]

at idle the timing with vacuum should be 15 degrees, at 2000 rpm timing runs about 20-25 degrees, and at WOT wide open throttle timing runs 32-35 degrees just and fyi

Thank you. Good to know.
Which leads me to another question. What should the rpm's be once the vacuum line is connected and the timing is at 15*?

[Srdayflyer]

i run mine at 700 +- 50 a/c solenoid should kick it up 100 when the a/c is on

[will e]

i run mine at 700 +- 50 a/c solenoid should kick it up 100 when the a/c is on

The solenoid is an anti-diesel device, not part of the AC system.

[Srdayflyer]

i beg to differ on that but thats why this forum exsists, thying to keep out classics alive and yes it aids in anti dieseling but with the a/c on it does kick the idle up other wise the a/c draws down the idle quite a bit sometimes to near stall, my holly sniper is wired to the a/c lp switch when i select the a/c on the idle kicks up 100 rpm , those york (piston type compressors)take a lot of energy compaired to a sanden (vickers) style compressor thats why amc switched to them in the last few years of production to squeek out a bit of fuel economy. not that your gonna change the aerodynamics of a flying brick going down the hwy.

[will e]

79 wiring diagram.jpg

This is from the 79 Jeep wiring diagram. It is specified as the anti-diesel solenoid. It is connected to the same circuit as the electric choke. Both are powered when the ignition is on. It is not integrated into the AC system.

[tgreese]

These devices are installed for either reason. Suggest you need to check the TSM to resolve this - an anti-dieseling solenoid will be adjusted so the throttle plates close completely without power (ignition off), and normal idle when energized. The solenoid could be adjusted for an idle boost when the AC is on. The same solenoid could have either effect. The device (solenoid) has two states - on or off. How it functions depends on when the solenoid gets a signal.

[will e]

From the factory I have never seen it used to 'step up' the idle for the AC compressor. One thing to note is that the solenoid is not very strong, it often cannot 'push' the throttle open. It is strong enough to keep the throttle open. If it was connected to the AC system it wouldn't be effective at idle if the compressor was cycling.




1986 AC diagram. No indication of a solenoid for the carb as part of the AC:
https://oljeep.com/gw/elec/86/86_FSJ_Wi ... age3-3.gif
Under hood it is connected to the same circuit at the electric choke
https://oljeep.com/gw/elec/86/86_FSJ_Wi ... age2-6.gif

1983 under hood. Connected to same circuit as the electric choke Also note that compressor wire is shown.
If it was used for AC it would have been most likely spiced into the compressor circuit. https://oljeep.com/gw/elec/83/83_FSJ_Wi ... rtment.jpg

1988 under hood. Connected to same circuit as the electric choke
https://oljeep.com/gw/elec/88/88_FSJ_Wi ... mPage1.jpg

[OldFarmTruck22]

For what it is worth - When activating A/C with any running engine, there is a natural power draw put upon the running engine that lowers rpm if not assisted by an 'idle kick-up' UNLESS this engine is computer controlled. Engines do not 'naturally' adjust their own rpm when load is applied. I know that these AMC 360's or 6 cylinders are LOADED with smog and vacuum junk from the factory, but I guarantee you there is an electronic connection that bumps that throttle up when the A/C is kicked on.
Even engines that are stripped of all factory smog and vacuum parasites require an additional solenoid to raise rpm when the A/C is activated.
Call it what name you might on the factory trimmed engine, but there is DEFINITELY an A/C kick-up solenoid built into that factory carb linkage. What you read as 'anti-diesel' device may also be wired to kick up idle when A/C is switched on.

[will e]

I am sorry oldfarmtruck22 but you are incorrect. I've traced the lines in my own rigs. I've linked wiring diagrams which show it as an anti-diesel solenoid connected to the ignition system and not connected to the AC in any way.
I searched on vintage air for solenoid, they don't sell one. Their kits don't include one.

There are aftermarket kits that use a solenoid to bump up the speed but our trucks did not do this from the factory.

I also thought they were for the A/C at one time. And, related to the OP topic, I thought 'ported vacuum' got stronger as the engine speed increased and increased the ignition timing on the distributor.

It is possible I am wrong, I never say never.
 

[Srdayflyer]

well guys
here is the info direct from the fsj manual section 1J-49/50 states the part in question is called the sol-vac throttle positioner. not and anti dieseling solenoid, without spending a whole lot of tine typing it verbatim has 3 positions
off, deactivated ,position (curb idle) , the holding solenoid position, and the vacuum actuator position, it is an electro- pneumatically controlled solenoid that and increases the idle if the intake manifold heat , A/C , or rear window defogger are in use or energized , those are the FACTS there are about 2 paragraphs explaining the operation you can read the factory FACTS yourselfs , just to clear fact from fiction

[will e]

That's great. Which manual?

[Srdayflyer]

its, in the factory maintenance manual, and the wiring diagram might list it as an anti-diesel the manual jets into the nuts and bolts of what does what ,when ,how and why, after 1975 when the government got more increasingly worried about your being able to breath fresh air and not have you driving a horse and buggy again their ever changing emissions controls ,
their are so many vacuum temp switches and lines its why most of the problems we run across are in part due to failed parts ,vacuum leaks electrical wiring problems in these rigs, my cherokee (big MINION Hauler) i spent over 200 hours gutting 80% of the emissions equipt. , repairing chaffed wires, repinning connections, removing wiring that supported bogus E PARTS, a lot if which are no longer available, the most notable are the AMC adapted motocrap ignition system , the fomoco carb 2100 series, and the elecrto mechanical/pneumatic cruise control, having replaced them with holly hyperspark ign, sniper EFI , and rostra cruise control, and nor pass emissions check with flying colors and i can actually see and work on the motor, and not worry about reliability, and being stranded , ive spent 4.5 years completely doing a mechanicals ground up on this truck and have run into just about every issue and problem associated on fsj's , i have a very solid understanding these trucks anyhow thats my take on ramblin on.

[will e]

Well, there in lies the confusion. You are referencing a different device. The 'sol-vac' is both electronically and vacuum operated.

http://gleebledorf.com/solvac.html

I am referencing the anti-diesel solenoid.

Both exist in the real world. I have not had the occasion to work with a 'sol-vac'. Do you know what year they were introduced?