Surging Under Load - I REALLY need to get this figured out.

[FSJ Guy]

Sounds like fuel starvation to me, since it idles OK and only seems to occur under load.

I think your Duraspark is probably fine. The one thing I see you have not replaced is the distributor pickup coil. Unless you've replaced the entire distributor before, maybe try replacing the pickup module??? Yes, you can buy it separately.

[Dr. Marneaus]

I have never replaced the pickup in the dist. If it was bad, wouldnt it just not run?

[Tatsadasayago]

It is possible for the pickup coil to fail under load and heat. I kinda doubt this is your problem, but never say never when JEEP is involved. Another possibility is that the pickup is fine but the distributor shaft is bent/bending with heat or the shaft bushings are loose. This will cause intermittent spark as the reluctor gets too close or too far away from the pickup. This is usually manifested as a part throttle miss and not a full on failure like you are experiencing.

I don't know what it was about Reno air/environment back in the late 80s but I saw several pickup coils literally come apart causing the small copper wire to corrode to a green color and wrap itself around the reluctor. I was amazed these vehicles could even run.

Again, never say never when JEEP is involved

[Stuka]

I have had pickup coils fail due to heat. Always took them like 15 mins to start working again.

[Dr. Marneaus]

Okay so I followed the directions in the other thread. I believe I have achieved best lean idle.

I set my timing based on vacuum. This turned out to be something like 33-35* total timing when hooked to manifold vac. Removed vac and checked and it was like 11-13*

I pulled 6 of my plugs and they all appeared decent. Toasty brown, not black not scorched white. However one side of each plug was brown the other side was mostly white, I assume intake vs exhaust valve sides. Not sure what that means if anything.

Then I checked that the vac module on the dist worked. It did and it held solid. With my vacuum pump it appeared that the vac advance was maxed out around 15" of vacuum. It didn't move after that.

While doing all of this my vacuum gauge read right around 16" 16.5" was as high as I could get it. Yesterday I tested my vac gauge against my vac pump and the gauge read about 1" lower than the pump at any point I stopped so I assume that means the gauge reads a little low and I was around 17" vac. As mentioned I live at about 5000' elevation.

That's all I did today.

[Dr. Marneaus]

This is the same plug. The others were pretty similar not not as extreme a difference






Here was another plug

[will e]

I don't have a points dist. Even my old engine had been converted to some optical pickup thing. I've never had points on a vehicle.

You don't know what you missed. Dual points were even worse. I have NO IDEA how the Chevy guys with the distributor in the back of the engine put up with it.

[FSJ Guy]

When I've had the distributor pickup fail, it usually failed without warning and it simply failed. No intermittent operation at all.

First time, I think it was heat, as once it was towed home, it fired right up the next morning. The second time, I didn't give it a second chance and simply replaced it.

[Tatsadasayago]

Your first plug shows it's been running on the lean side of 14.7:1 with a bit of fuel wash from the intake valve. The orangish color is likely from an additive.
Note the heat penetration on the threads is about half-way to the washer? I'd say the chamber temps were a bit high and is consistent with a leanout. Also note the rounded edges of the electrode. Things were getting a bit warm there.
The last plug shows some oil consumption, but otherwise the same as the first one.
Of course, the new timing setup makes these plug readings a moot point and a fresh set would tell a different story after 50+ miles or so.

Your vacuum and timing numbers are actually quite good considering your altitude. I would wager you could probably get away with a few more degrees of base timing and not have any problems...and maybe even pick up some power.

The more I learn about your setup and issues, the more I am convinced it's a fuel pressure/flow issue and the plugs just add to the body of evidence.

[Tatsadasayago]

Oh, and back in the day I used Spooner summit as my testing ground. If my rig made it from the valley to the top without falling on it's face or melting down, I knew I had it dialed in! I broke in many an engine on that highway

[Dr. Marneaus]

Thanks bud! You're being pretty helpful!

So next step would be? I can do a new set of plugs and give em a reading this weekend. If it's running just plain lean I can jet back up one step on the chart. I believe I am running 3 stages lean in cruise and 1.5 stages lean in power mode (number 12 on the edelbrock 1406 calibration chart) I really don't remember but can look at my jets and rods tomorrow. If I'm still showing lean I can bump back up a little.

Not sure how much effect it would have had but I assume I was running lean down in Boonville and Sonoma area l the way back until past auburn. I leaned everything out to run decent here at 5k so there was likely a big difference at under 2k

But carb tuning aside, I hVe still experienced this issue.

Where should I look next?

[Dr. Marneaus]

Run a temporary fuel pressure gauge so I can see what's up?

[Tatsadasayago]

Yes, a temporary gauge would tell you a bunch.
I would also pop the top off the carb and take a peek for dirt etc.
Another thing to check is float levels. AFBs/Edelbrocks are sensitive to float and float drop levels, so confirm your measurements meet the factory specs. If the floats level is set too low, the needle closes off fuel too soon and the bowls empty rather quickly under load. Too high and you get flooding on even the slightest inclines.

If you don't find anything inside that seems wrong and you have a manual choke, you can close it when the engine is doing stupid things. If the engine perks up when you get about half closed, you know you are leaning out.
Obviously this won't work with an electric choke.

Good luck!

Jim

[Tatsadasayago]

Oh, and fuel tank venting...

[Cataldo]

Tats is on the money here!

Plugs, tank venting, and needing to put on a fuel pressure gauge. Try driving without a gas cap first, that rules out venting issues.

Go 1 heat range cooler on the plugs as well. Looking at the heat on your threads, it should be about 3 threads of discolor not half the plug.

Also what is your full mechanical advance? base, mechanical at ~3000rpm or wherever it stops advancing and then vacuum advance on top of that. What are those numbers?

[Stuka]

Plugs, tank venting, and needing to put on a fuel pressure gauge. Try driving without a gas cap first, that rules out venting issues.

Good idea to try. If your tank is generating vacuum because of a venting issue, it will cause fuel starvation, but only under high throttle use cases.

[Dr. Marneaus]

Cool thanks guys. Also I. An almost guarantee my tank is not creating a vacuum. It has a minor leak first of all, on the top. Second my gas cap does not completely seal if I do not want it to, and on this trip due to experiences from the past, I left it a little loose to make sure it wouldn't create too much pressure inside from the heat.

I will, however, further investigate the venting deal

[Dr. Marneaus]

on the whole fuel starvation thing...is it possible my fuel filter simply is too small and restricting flow?
Trying to determine the best methof of installing a fuel pressure gauge as well.

I already have an inline fuel filter near the carb. I can probably just remove it for now (keeping the rear fuel filter) put a barb coupling on each end of the existing fuel lines, then run hose up to the gauge/Tee fitting, then back down under the hood. I think. I'll have to investigate tho.

[Dr. Marneaus]

just realized my vacuum gauge is also a fuel pressure gauge. All i got to do is replace my under hood fuel filter with one of these and install a 1/8" barb then snake some 1/8" fuel line up through the cowl and stick my vacuum gauge under the windshield wiper or something.

[Stuka]

on the whole fuel starvation thing...is it possible my fuel filter simply is too small and restricting flow?
Trying to determine the best methof of installing a fuel pressure gauge as well.

I already have an inline fuel filter near the carb. I can probably just remove it for now (keeping the rear fuel filter) put a barb coupling on each end of the existing fuel lines, then run hose up to the gauge/Tee fitting, then back down under the hood. I think. I'll have to investigate tho.

Certainly possible. Fuel filters typically have a GPH rating, although OEM style ones rarely state what it is. Also possible the sock is plugged up a bunch, when when you need a lot of fuel, it starves the engine due to lack of flow.

I am thinking the gauge will tell us a lot. Either it will say fuel is the issue, or that it is not the issue.