growing issue, backfiring, stalling

[dvandervossen]

Have 81 CJ8 that ran fine for a while, but now has a progressing problem. Mostly finished it about a month ago. First couple weeks no issues, even did a couplee 2 hour drives. Had out on a trail on a overcast/drizzly day, puddles on trail. Drove about 6 hours on trail. First issue hit last 15 minutes on trail. Thought just ran out of gas. Then when leaving trail for hotel started having issues under load. From there it took 45 minutes or so till it started acting up the next couple times I drove it, but has gotten progressively shorter each time. Sputters & backfires from tail pipe, then stalls when pulled out of gear. Starts in 4th gear and progresses quickly down the gear range as you drive. Now can only go a couple miles or so before it starts. Thought it might be a heat soak issue, but ran w/ hood off and had same issues. Have replaced ignition/distributor w/ DUI high performance. Sleeved fuel line. Carb is reasonably cool to touch w/ hood off. Problem persists. Thinking heat range on plugs or carb issues.

Holley carb

Previous owner swapped the 4.0 block in (date stamp 1997) but put all the original AMC 258 i6 / 4.2l accessories back on. I took everything off and cleaned it up when building the jeep, but not go into an internals on Carb or engine.

Thoughts?

 

[Lumpy Grits]

:ww:

Make sure the tank is full-
When was the last time the fuel filter was changed?
Remove the gas cap from the tank, and see if anything changes.
LG

 

[Torxhead]

Ignition timing comes to mind, you did set it with a timing light right? You could verify the #1 tdc aligns with the timing mark on the vibration dampner. The ignition control module wherever it is mounted should be properly grounded and not getting hot to the touch. Make sure you have a set of spark plugs designed for your engine and not for the high tech computer controlled engines. The carb can be an issue also, make sure it is not dumping gas into the engine like maybe from a float that is stuck open.

 

[Lumpy Grits]

Bad electrical GND, is a common issue with all CJ's...........

One other thing-Put a wrench to ALL manifold bolts, and the carb's base.

LG

 

[R717]

Backfiring through the exhaust, not the intake, correct? Out the exhaust indicates intermittent ignition. Through the intake/carb indicates lean or ign timing. If it's intermittent then it's probably not ign timing. At what point did you put the DUI HEI distributor on? Did it make any difference at all? Next trip bring a multimeter with you, when it stalls, leave the ign on, and quickly measure voltage between batt + on hei dist and negative post on battery. If it's less than 12V you know your issue is resistance upstream of the ignition. To his isn't a definitive test, but it can help narrow down where to look.

 

[dvandervossen]

Backfires thru exhaust.

Issue started with "stock-ish" ignition computer, distributor, coil, plugs, wires

I installed DUI distributor & new wires, eliminating stock coil, distributor, sires and ignition computer trying to resolve the problem. Problem still persists.

I did wire from a larger (probably 12 gauge) 12volt wire that went into the ignition computer and eliminate the resistor wire before the DUI. Since issue existed before and after DUI, the voltage drop issue does not seem likely. The volt meter does fluctuate some, but typically between 12 - 15 volts. haven't seen below 12 while running.

I picked up some Autolite APP985 plugs that I am going to install. That would be last part of ignition system I can think of in terms of parts.

Timing was set w/ original distributor and the w/ DUI both at 5 degrees w/ the vacuum advance line pulled off and then vacuum line reattached.

Think I am thru most of the possibilities on the ignition side.

Have been doubtful that it is a fuel starvation issue since I essentially have fuel coming out the tail pipe, but filters etc are next on my list to check. This does correlate some with it getting shorter and shorter each time (as filter gets more and more clogged). Will have answer on this in the next day or two, as soon as I can get back on it.

New thought came up recently that maybe the exhaust valve springs are worn out & I am getting fuel mixture past them & losing compression as soon as they heat up enough to lose a little stiffness each time. Not nearly as easy to check or fix, so hoping not. But this would match up with the issue of it happening earlier and earlier in each ride.

Thoughts ???

 

[mtnwhlr]

Are you running a Cat?

 

[elwood blues]

What kind of Holley carb? With everything that you've replaced on the ignition, I'm wondering if it's in the carb... but... :dunno:

 

[Torxhead]

So, just what spark plugs are you running now? I would suggest Autolite 985s, and not the double platinums. Gap them at .045"

 

[dvandervossen]

No Cat - Flowmaster 40 & 30" cherry bomb behind that

Don't know how to identify which Holley carb it is.

 

[elwood blues]

Don't know how to identify which Holley carb it is.

https://www.holley.com/blog/post/how_to_identify_your_holley_or_demon_carburetor/

Do you know how old your carburetor is? Are you comfortable rebuilding it?

 

[dvandervossen]

2300 series

went ahead w/ several of the suggested fixes

checked filters, tank sock, etc. all clear.

replaced plugs, installed new alternator as terminal was loose

rebuilt carb

things do appear better. have done (2) 10 mile trips. Think carb still needs some adjustment. but significant issues I was having seem to have wained.

Looking around for an old school shop to adjust the carb better. Also not sure what timing I should set it at. Everything I look up on the 4.0 says its computer controlled and not adjustable. Which would be great if that was true in my case. However, since the engine was swapped in and all the AMC 258 i6 / 4.2l accessories put on it, its not computer controlled and I need to set timing. Currently its set at 5 degrees.

 

[elwood blues]

Okay, that sounds like you're on the right track. Have you ever set timing with a vacuum gauge? Honestly, with your unique setup, I don't know what to tell you about setting the timing. Get the carb tuned correctly will help.

My 2¢ about it, not knowing if you have a 500cfm or 350cfm 2 barrel carb is kind of an issue. A 350cfm may be a little to big, a 500cfm is way to big. The 2300 series is a good carb, but if you don't know how to get it dialed in, you're going to keep having issues. I would suggest changing to a Motorcraft 2100 series, which is very similar, but available in smaller CFM ratings (unfortunately they're all used, they don't make new ones since the 90's), or a Weber carb.

Here's a couple of links to Holley 2300 carb tuning procedures


https://www.google.com/url?sa=t&sou...FjAMegQIAxAB&usg=AOvVaw2_MHAHjpLBgfPNGRiwP5gZ

https://www.google.com/url?sa=t&sou...FjASegQIBxAB&usg=AOvVaw3T_AcgVAXMRGmjyqc6JK7j