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Hei timing and vacuum advance help!

11K views 18 replies 5 participants last post by  Luckymac 
#1 ·
Hi everyone over the last week i installed a new hei distributor. It already runs waaaaayyyy better than it did with the nutter bypass but the acceleration has taken a pretty substantial hit. I have the timing set at 9degrees before TDC and it better than it was but still not great. It might be because it wasn't totally warmed up before test driving it today between severe thunder storms. Also I have absolutely no idea how to set the vacuum advance. So if anyone has any ideas I'd be happy for the help! Thank you all
 
#2 ·
Need to post your Engine and Year?, Carb or injected?

You need to find a ported vacuum source for the advance. What brand of HEI do you have? Most vac advance diaphragms have a set screw that can be adjusted internally.

Grab an inexpensive vacuum gauge, if you don't already have one, connect it to your vac line at the dist. the vac should rise as you advance the throttle, 26 to 28 hg was the best I could get out of my 4.2l.
If it goes backwards on throttle increase, you are connected to a manifold vac source and need to find new source. If your carburated, go for the lowest port on the carb. If your injected your outside my expertise, someone else will chime in I'm sure.
 
#4 ·
You should be pulling all your smog off and tossing if you haven't already,unless you need to pass a visual on emissions equipment. Use the port at the base of the Carb on the side facing the valve cover and run a single Vacuum line to the Vac advance. Your HEI installation instruction sheet should tell you whether you need to do anything with the Dist. vac diaphragm or not. 9* is a good start to your timing. remember to set it with the vac advance line disconnected and capped and the engine at running temp and the choke fully open.
You will also need to set your idle mixture screws with a vacuum gauge to obtain the highest vacuum you can get at Idle, helps to clean up the stumble just before you start to accelerate.
Last thing, A fresh set of plugs makes a huge difference at low rpm. Use the inexpensive copper core champion or autolite. I found out the fancy platinum, etc actually perform worse and don't last long.

Good Luck
 
#5 ·
I'm not sure what the rest of the smog stuff is. Lucky in New York anything over 25 is exempt from emissions. Thank you so much I seem to have been on the right track but it really helps to have someone who's been here before to help clarify!

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#6 ·
With your setup, about the only thing you need for vacuum is the Dist, front axle cad on the front axle for in and out of 4wd, the line into the cab for your heater/defroster doors and the charcoal canister. Everything else not being used can go. just make sure to cap off anything you pull off the manifolds, anything vacuum not being used and uncapped or leaking will affect performance
 
#7 ·
I think I took all that out already anyway, I knew I didn't need the canister and my cad never worked anyway I just put a stud on the fork and welded it in. And I'm pretty sure all my heating stuff is cable driven because I'm still technically an "80s" YJ I might be wrong though

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#8 ·
There are vacuum solenoid actuated doors in the cab that change direction for the defroster. That line goes into the cab at the top of the firewall just behind the carb a little to the left. If you pulled the canister them make sure your EGR and CTO valves on the manifold are plugged or capped
.. I went cable lock on my axle so I pretty much pulled anything and everything else along with the wiring. tore the harness open and removed one useless wire at a time until I ran out of anything that wasn't connected after making sure everything was working before pulled each wire, then I replaced the dried out wire wraps with all new. Cleaned up under the hood nicely, easier to work on without all the garbage.
 
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#11 ·
Just by chance do you have an advance adjustment knob on your timing light? That may be giving you the wrong timing mark reading,
 
#12 ·
Glad you have it running great though, " I love it when a plan comes together".LOL
 
#13 ·
22* BTDC is too much. Are you sure that you have the wires in the correct place in the cap?
Another thing to check is your timing chain.

10* to 12* should be the sweet spot for HEI timing. Did you re-gap your spark plugs to .045"?

If your timing chain is good (you can listen to the front of your motor and don't hear clattering while running), and the Jeep runs well, I wouldn't worry too much about the plug wires being one space out in the distributer cap. You may have compensated for it by advancing the timing to what it is.
For me though, I would prefer everything to be in the "factory recommended" spec.

Check out Got it at lasts #11 post. The timing thing could be as simple as that.

Good Luck, L.M.
 
#15 ·
The only other thing I can think of is the distributor could be installed a tooth off.

Good luck, L.M.
 
#19 ·
What hasn't been mentioned is that the crankshaft pulley (also called a vibration dampener) is made up of an inner hub that bolts to the snout of the crankshaft and an outer ring with the timing mark on it. The two parts are joined by a rubber ring between them. If the rubber ring deteriorates (it could be 30 years old), the outer metal ring can move and make proper timing impossible.
If this happens, the cure is to replace the crank pulley. I poked around the most popular sites and didn't find any. Perhaps they are still available from MOPAR.

Good Luck, L.M.
 
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