Lean (PING)

[jeremy5780]

Installed the mc2100 on my 85 CJ7 AMC 258 i6 / 4.2l with the team rush upgrade I was having a ping real bad on acceleration around 10-11 btdc through all gears, but it was idling like butter. I have my mixture screws backed out 1 3/4 turns with 19-20 psi and 750-800 rpms. So I backed my timing down to 8 btdc and it idles a little rougher than 10 btdc but it's still a lot better than the previous holley. So I took it for a test run and the ping can only be (slightly) heard in 3rd gear at the top of the rpm's, when I really mash the gas down. If I gradually give it gas there is no ping. I tried to drop it below 8btdc but its just to rough. I really dont thinks it's that bad but I wanted to pick your brains on the subject!

 

[IOPort51]

What octane gas are you using? I know regular is what you want to burn and if it had no ethanol in it that would be the best choice. jumping up a grade may be your best option.

 

[jeremy5780]

Running 89 octane with stock autolite copper plugs gapped to 50

 

[Torxhead]

Running 89 octane with stock autolite copper plugs gapped to 50

So, try backing down on that .050 spark plug gap and see what happens. The vacumn advance rate can be adjusted by inserting a 1/8 allen wrench into the vacumn advance canister hose inlet, but I would suggest you keep track of how much you adjust it.

 

[SCSEAJAYSEVEN]

Reduce your spark plug gap to .045. That should help. If not reduce the gap to about .042. Too much spark is just as bad as too little...

 

[mstar]

Jeremy, if you have a understanding about ignition advance you might want to start by determining the total mechanical advance and then the vacuum advance.Sounds like your advance setup is screwed up. Not enough at idle ,to much total advance.this can be corrected .mike

 

[jeremy5780]

Mstar you lost me, I'm not sure how to check that.

 

[mtnwhlr]

Jeremy, if you have a understanding about ignition advance you might want to start by determining the total mechanical advance and then the vacuum advance.Sounds like your advance setup is screwed up. Not enough at idle ,to much total advance.this can be corrected .mike

With the Team Rush upgrade it says to change your vacuum advance from a ported vacuum to a non ported which would give you more advance at idle and less total.

 

[jeremy5780]

So I need to disconnect my dizzy vacuum hose from the carburetor and hook it directly to the manifold?

 

[Dan77CJ7]

With a DUI distributor you can get rid of all that wiring and vac hose's if i remember you dont run emissions $350bux cleans the place up like a molly maid!!!! one wire two hoe's!!!

 

[Dan77CJ7]

*hoses

 

[mtnwhlr]

So I need to disconnect my dizzy vacuum hose from the carburetor and hook it directly to the manifold?

It was hooked to the upper part of the carb above the throttle plate which is ported, you need to hook it to a port at the base of the carb that is below the throttle plates which is nonported.

 

[mstar]

Jeremy, what i was thinking is to check your advance for total mech.Not sure about what these guys like to run but i think 32* to 36* should be OK. If you want to set it at 10* initial than you will want 22* to 26*
centrifugal advance.If all that checks out then move on to the vacuum advance.I am not familiar with the mods you have made so someone else can guide you for further adjustments.It may just be lean main jets or faulty power valve, etc.(lean will stumble and ping on light throttle) .
It sounds like you have made several modifications to your engine.Did you do one at a time and understand 100% what you did and why. mike

 

[jeremy5780]

Turned the mixture screws out to 2-1/2 turns and gapped the plugs to 40 and the Ping at max rpm in third has quited down a lot, I have to mash the pedal to the floor in third and almost over rev to hear the ping and when you do it's very faint.

 

[jeremy5780]

I disconnected the timing advance from the distributor and plugged it and it still has the lean ping, I'm wondering if it's the power valve? I'm not sure of the size in there now, it's from a standard rebuild kit from napa

 

[Neuner]

I took readings to map out the timing curve vs the RPM. I went in either 250 or 500 rpm increments, just can't remember. Not sure what I did with the excel sheet otherwise I'd post the graph. It helped show me where it needed tweaking. As I made adjustments or bounced between ported and manifold vacuum, I retook the readings for its effectiveness. I was able to get a smooth idle at around 5-600, no ping and really good power using 87 octane.

I read arguments all over the internet on manifold vs ported, distributor settings and initial timing but it wasn't until I graphed it that I was able to tweak it for my setup and equipment.

 

[Neuner]

Found the first one I did with the initial settings and off of ported vacuum as an example:

 

[IOPort51]

Is your graph measuring vacuum or deg. of advance or both?

 

[Neuner]

Is your graph measuring vacuum or deg. of advance or both?

All three, vacuum measurement (port or manifold), centrifugal timing (ported and manifold disconnected with dizzy plugged) and combined timing with either of the vacuums attached.

After doing the port, I mapped the manifold which only increased the initial timing for a flatter curve. No matter what I did, my setup did not like manifold at all but I could see through the graphing and adjustments how it would benefit others depending on how they had theirs.

 

[Lumpy Grits]

CK the base area on your carb. They are well known for vacuum leaks that will cause a lean fuel mix. A lean mix can lead to 'pinging'.
Use VERY soapy water for this ck, and see if the bubbles get pulled inside.
Also make sure ALL of your manifold bolts are tight. Use the soapy water here too.
LG