setting engine timing -- vacuum advance mid 20s?

[BenM]

we got it adjusted to whare we have about 10 degrees at idle (with the vac plugged in) and peaks out about 35 at 2000 rpm. and we were actually able to put some miles on it too! we drove it from his house to mine about 15-20 minutes away. car felt like it was surging and still falling flat mid range almost as if it was working too hard definatly wasnt as bad as it was before lol. got it in my drive and popped the hood and the exhaust manifold had a slight glow to it. temp barley got into the green line... ive got another ignition box here out of my 84. could it be the box thats causing the surging? as far as the glowing goes too lean? idle screws are about a full turn from closed. they were initially set at 2. car definatly doesnt load up any more lol.

Based both on the hot manifold and the surging, I'd suspect the box. Misfires and unburnt fuel/air mix in the exhaust can overheat the manifold.

But first, check all your spark plugs and see what they look like, that will tell you something right now.

[kajsdf]

we've got a known good box that will be swapped in today. i will check plugs as soon as i get home.

[captspillane]

This is a great thread. My Spirit had Gronk's kit on it when I bought it. It ran terribly and I never got it straightened out properly before stealing that engine for my MPI SX4.

One thing I did find was that the distributor hold down clamp was never tightened by the previous owner. Its embarrassing how long it took me to figure that out. The distributor was free to vibrate and spin freely. That is a simple reason your timing would change value randomly.

[GRONK]

Could also be a leaking intake manifold, bad PCV valve, bad plug wire, mis-config on plug wires, etc.

[kajsdf]

pcv valve is good. we sprayed all around looking for leaks and found none.  could be plug wires, but they were changed when i did tfi upgrade. i've heard they can be bad out of the box. just a simple resistance check, or is there a better test?

at this point my list of suspicions is:
bad ignition box
bad plugs and/or wires

still need to dial in proper vac advance but i think that will be easier once electrical issues are ruled out/eliminated

[68AMXGOPAC]

The only time I have ever seen glowing red exhaust manifolds is when a friend put the distributor in 180* out on an Olds V8 - we drove it for quite a few miles before it got real doggy , got out and opened the hood and they were glowing cherry red...................not saying that's your issue , just commenting.

[eaglefreek]

How did the car run before the carb swap? In my experience a glowing exhaust manifold has typically been a timng issue. A couple possibilities could be either the outer ring slipped on the crank damper or possibly your timing chain might have jumped a tooth.

[kajsdf]

car didn't run great before carb swap.  however, we have some findings to summarize:

1. assuming anything is supposed to be easy is a bad assumption.
2.  having a tach is very important -- idle by ear is only so accurate. (however, we were VERY close.)
3. setting timing properly by altitude is vital.
4. there is a vacuum adjuster screw in the distributor.  it needs to be set up to get proper advance.
5. glowing exhaust manifolds are not good. in our case, this indicated that we were running far too lean.
6. church or other vacant facility parking lots make excellent testing grounds to avoid irritating the neighbors.
7. vacuum gauges are underrated.  go get one.
8. constant jokes improve morale.
9. removing the computer after it's bypassed (and the associated wiring "brain stem") is an extremely liberating feeling.  (don't forget to re-connect the yellow wires going to the 2-wire connector on the ignition box or you won't start.)
10. seafoam is amazing.  it really does work.
11. paint works excellent to identify timing marks.
12. a/c hoses and heater hose should be removed if possible to pull valve cover with ease.
13. removing the head and lifters and reinstalling head and lifters was far less frustrating than these timing issues.  and easier.  and even though the tsm does not state that priming is necessary, it is an excellent idea.  a priming "tool" can be created using an old distributor shaft and a drill (be sure to rotate in the direction of the engine and DON'T hit the cam gear.)
14. there is no such thing as an overabundance of assembly lube.
15. keep face and limbs away from carburetor while timing.  backfires can hurt.
16. speaking of things that can hurt, exposed wiring on the coil to distributor can bite pretty hard.  it's funny as a spectator, though.
17. swivel sockets are amazing and will save your sanity.
18. don't drop intake bolts onto your motor mounts.  this is a frustrating area to retrieve them from.

i am sure there were plenty other excellent lessons.  if anyone would like any clarification on any of the above points i will definitely elaborate. 

final note of what we did:

-installed new lifters (this was the easy part)
-timing set at 12* base (due to altitude -- gronk explained this excellently earlier in the thread)
-carburetor mix set 2 turns from all the way in, fairly rich (may adjust later -- seems to work well for now)
-distributor vacuum advance adjusted at least 10 turns from initial setting (set to carter settings, but we are unsure of original/specific settings)
-idle set at 750 rpm
-choke still needs to be properly set up, we are running it tied open at the moment
-new spark plugs -- old were disgusting and covered with trash, even though they were fairly new.  buildup due to poor performance with the carter and our various attempts at tuning.  highly recommend changing, this will make things easier.  these were what was causing our surging.
-computer completely removed -- there is a yellow wire that runs to 3 or 4 wires spliced together that needs to be hooked up to the ignition box if you remove all the wiring.  this will be fairly easy to identify as it is the only bundle like that. 
-installed aftermarket tach.  will likely replace at some point with something mounted inside the dash, like the clock -> jeep tach conversion thread.

we still need a little fine tuning, mostly with the vacuum advance -- this involves a LOT of trial and error, even after timing is properly set.  there were a few good threads we found on some jeep forums that posted distributor curves and other such information (links to follow later). 

at this point the car is now definitely drivable and the performance is definitely above the carter's.  carb conversion is, of course, highly recommended.  new lifters were a great improvement as well, although we did not replace the cam as most people recommend -- i will be rebuilding this motor at some point in the future and changing out the cam/matching lifters when that happens.

hopefully this helps out some of you that may have run into these issues or have hit a roadblock.  any questions or clarification needed, just ask.

[68AMXGOPAC]

I would like a video of #15 and #16 : ) - #10 is so true - great stuff.

Sounds like you have more of the bugs worked out - great percervierence (sp) .
Good story too : ).

[carnuck]

One thing I forgot to mention that occasionally plagues AMC 6 cyls (until the 4.0L came along) and that is cam walk. They put in a cam button from the factory to overcome that trouble. It's an "easy" add-on  to the 4.2L with the cam bolt and timing cover from the 4.0L (and a miteaswell timing set)