Spankrjs 1985 Spring Special CJ-7


Scrambler Junkie
I did some more diagnosis, trying to figure out my "slight surge" at light cruising speeds/throttle input.

With the vacuum advance disconnected, the problem goes away 90%. The issue is still there, just not as noticeable. So, I was thinking, maybe the vacuum advance diaphragm was leaking, or the linkage binding up, maybe?

This is the vacuum advance module, on the side of the distributor:


The OEM tag that is on it:


Basically, engine vacuum, either ported or manifold (depends on year/emissions stuff, check your under hood sticker), pulls on the diaphragm advancing the timing as vacuum increases. This is kind of when I am having my issue, right off idle, into more of a light throttle mode, when the vacuum is increasing, should be increasing the timing.

So, I hooked up my little hand held vacuum pump to the vacuum advance module:


Put 20" of vacuum on it:


The diaphragm held the vacuum for 20 minutes. Vacuum never started to drop, I finally just released the vacuum. So, I am assuming no vacuum leak here.

I pulled off the distributor cap and checked how smoothly the vacuum advance arm was moving. It moves really smooth, I don't think anything is binding up. I was hoping maybe the inside of the distributor had some debris inside, causing an issue, but nope, it is clean.

No vacuum applied, arm rests here:


Full vacuum applied, arm moves to here:


Not the best pictures, but the arm moves nice and smooth throughout its entire range of motion. No skips, bumps, erratic movement, nice fluid stroke.

So, I do not think my issue is with the vacuum advance module. This was an easy thing to check. I will probably hook up a vacuum gauge inside the cab to check vacuum while the engine does its "surge" thing. It will only do it under load, part throttle cruising. Idle, hard acceleration, stationary throttle increases, no problems, Starts up and turns off fine.

After looking at the vacuum, I will probably check the fuel pump pressure/discharge capacity. Then, check the carb again. Just kind of funny how this problem just happened, not right after I rebuilt the carb, who knows? Maybe I dropped some old RTV down the carb throat when I was messing with the valve cover re-seal?

Speaking of valve cover re-seal, fail :(


Yep, the plastic valve cover started to leak, but only at the back, near the firewall. I am almost wondering if the mushy/shot motor mounts/transmission mounts allowed enough engine movement for the valve cover to hit the heater box stud, jarring the seal loose? Before I proceed with either resealing/replacing the valve cover, I am going to change the engine/transmission mounts. When I was draining/refilling the transfer case I realized that I could actually pick up/lift the entire engine/transmission/transfer case assembly!!! Time for some new mounts.

I was talking about how the vacuum advance is run off either ported/or manifold vacuum, this is how my '85 California emissions model is run:


Hard to see, but I have a line that runs straight off the intake manifold, to a small vacuum reservoir, through a forward delay valve, to the adaptive switch. Before the adaptive switch/reservoir/delay valve, the manifold vacuum line "T's" off straight to the vacuum advance module.

So, I am getting full manifold vacuum to the vacuum advance at idle. This is probably due to the under dash computer controlling some of the timing.

IIRC, I set my timing at 8 degrees advance:

1) engine RPM at 1600
2) vacuum advance module disconnected/vacuum line plugged
3) adaptive switch electrical connector unplugged.

When you hook everything back up, I can't remember what the base timing actually is at idle. But, it is higher then the initial 8 degrees. So, you have base timing, plus mechanical advance, plus vacuum advance, PLUS the computer controlling some of the timing.

On the computer affecting the timing, this is why when people do the "nutter bypass" you have to remove one wire from the ignition control module. This is how the under dash computer controls some aspects of the timing, via the ICM which talks to the pick up coil assembly inside the distributor. I am assuming the computer is using the pick up coil as a rudimentary "cam position sensor"?

After I check out the possibility of any fuel issues, I will recheck all the timing stuff, and map out the mechanical/vacuum advance curves.

That's it for now :wave:


Scrambler Junkie
I did some more diagnosis work last night.

First, I wanted to check manifold vacuum, while driving. I wanted to see if I had steady manifold vacuum throughout various RPM/driving conditions, especially when the surge occurs.

I inserted a plastic "T" at my manifold vacuum line, right before the little vacuum canister:


I had a really long length piece of vacuum tube, which I connected to my "supposed to be mounted in the dash but I keep it loose for diagnostic stuff" vacuum/boost gauge, voila:


The picture above is showing manifold vacuum, while the choke is on the 2nd step fast idle, around 900 RPM. 22" here, 24" at base idle RPM of 650.

Manifold vacuum highest at idle, drops as you smash the gas and the throttle plates open. Vacuum steady, smooth drop as you accelerate. Manifold vacuum DOES fluctuate when the engine surges at light throttle, between 10-18". Vacuum fluctuation matches the engine surge, so I am thinking the vacuum fluctuation is a "symptom", not a "cause" for my issue.

I just tested "manifold vacuum", I might go back and test "spark/ported vacuum", but I would imagine the results will be the same.

So, no vacuum leaks anywhere, steady manifold vacuum EXCEPT when the engine surges. I am going to "ASSUME", for now, that the steady vacuum reading is telling me that I do NOT have some weird vacuum leak some where. If necessary, I will revisit this potential vacuum leak scenario.

Next, decided to test fuel pump pressure and volume. I did not think this was the cause of my issue, but worth testing to eliminate the possibility.

My fuel pressure tester gauge is for "high pressure fuel injection" applications, NOT for low pressure carb fuel pressure. So, $35 in parts later I had a "low pressure" fuel pressure tester:




Basically, cheap fuel pressure gauge, 1/8 NPT "T" and two 1/8 NPT hose barbs, some fuel line and clamps.

NOTE - some people mount these gauges permanently under the hood. NO way I would trust one of these cheap gauges to sit on top of a hot engine. Too great a risk for a fire.

Anyway, FSM fuel pressure testing procedures:


At first, I mounted the pressure gauge between the filter and carb, bad idea. The gauge fluctuated terribly due to the excess fuel trying to flow back to the return port on the filter:


So, I removed the filter, installed gauge, got this reading:


This is higher then the 5psi mentioned in the FSM, BUT I am also "dead heading" the pump because I took the return line out of the loop. I am assuming my pressure is fine.


Scrambler Junkie
Next, I tested fuel pressure volume:


Both testing procedures are from my 1983 FSM. Interestingly, my 1985 FSM does not have these testing procedures??

One pint is 16 ounces. I did not have a 16 ounce container, so I figured a 12 ounce beer bottle would be good enough:


I ran a piece of hose from the metal fuel line straight to the beer bottle:


The carb will idle for awhile with its float bowl full. Anyway, in 18 seconds I had 12 ounce of gas, so no doubt in 30 seconds I would have had at least 16 ounces/1 pint:


So, I am pretty confident that my fuel supply/pressure, at least to the needle and seat, is good to go.

Even though I have "screwed around" with the idle mixture screws recently to see if a slightly enriched the mixture would eliminate the surge, it is till almost dead on. Note that the stepper motor pins are close to center at idle:



If you rev up the engine, they move around. If you hold the engine at high RPM, then manually shut the choke plate, causing a lean condition, the pins will move to the full rich side.

I am thinking that my issue is inside the carb, either a metering pin setting, trash somewhere, not sure. More diagnosis work needed.

I have been working through the FSM trouble shooting procedures, not necessarily in order:


From the above picture:

2, 4, 5, 10, 11, 12 all check out OK.

Still to check:

1 - float level inside carb
3 - inside carb
6 - check all timing (base, mechanical advance, vacuum advance, computer advance)
7 - 9 - inside the carb stuff
13 - pain in butt to check, but I do have the handy dandy AMC Feedback tester tool!!!

Anyway, I will probably check all the timing stuff next, then pull off the carb.

I am thinking I have a carb issue, but only one way to find out. My issue seems to be right around the time the carb should be transitioning completely off the idle circuit.

That's it for now :wave:


Scrambler Junkie
Had a little time on Saturday, and no rain for a change, so checked the ignition timing.


Used my older timing light/tachometer.

With the feedback carburetor and computer functional, there are a few steps to take before checking the timing:

1) Warm up engine
2) Disconnect/plug the vacuum advance line
3) Unplug the wire connector from the 4"/10" vacuum switch on the fire wall (if not, the computer will mess with the timing)
4) Hold the engine at 1,600 RPM.

OK, with all of that done, I was at 20 degrees advance, it should only be at 8. When I went to loosen the distributor, the hold down bolt was a little loose. So, I am thinking the last time I checked the timing, I left the bolt a little loose, and the distributor was slowly advancing itself.

Hard to see the timing marks with the radiator/water pump/front accessories in place, but this is what the timing scale looks like on this '85:


Amazingly, I took the above picture with the engine off, and the timing mark on the crank pulley lined up exactly where it was when I was checking the timing, 20 degrees advance. What are the odds of that!!!!!

And here is one on an '83 engine in my garage:


In hind sight, the next time I have the front of this engine off, I am going to paint the 8 degree mark so it is easier to see.

So, this thing obviously had way too much initial advance. With the base timing set at 20, and manifold vacuum adding around 12, I was sitting at 32 degrees advance at idle. I never checked, but I am assuming the computer might have been trying to retard it some :shrug:

Anyway, set the timing to 8 degrees advance, turned off the engine, reconnected the vacuum advance and the 4"/10" vacuum switch. Interestingly enough, my "static idle" advance was right at 20, 8 degrees initial plus 12 degrees from the vacuum advance (manifold vacuum).

So, that cured my "slight surge at cruising speed/light acceleration"? NO.

It made it almost go away, but it was still there.

Before I pulled the carb off. I got out some carb cleaner. I did the old "rev the engine up, cover up the carb with a towel so the engine sucks really hard and hopefully pulls out any crud stuck in some tiny port some where and makes it run good again" trick. That cured it.

So, timing way out, assuming a partial carb blockage some where, running great again.

The interesting thing about the timing being that far advanced, the engine always turned off and on instantly. No hard starts or "dieseling" when it was shut off. I am assuming the under dash computer must have been retarding the timing some :shrug:


Scrambler Junkie
After all the work to get it running correctly, decided to do some easy work.

The engine/transmission were really moving around a good bit, so I decided to swap out the engine/transmission/torque arm mounts. I used polyurethane, which I have used in all my other Jeeps without problems. I wouldn't mind trying rubber mounts, BUT all of the stuff you buy today is crap and lasts less then a year.

I used Energy Suspension brand parts:


Motor mount part#:


Transmission mount part #:


Torque arm bushing part #:


What the stuff looks like out of the packaging:


Important note on which way to mount the transmission mount, which I ignored, and then had to go back and switch around:


I started with the transmission mount/torque arm bushings first. I was able to reuse the torque arm stud, it was in good shape.

To change these mounts, I simply unbolted the transmission mount/torque arm stud from the skid plate, then used a bottle jack on the Dana 300 tail housing to raise the assembly up off the skid plate. Then, just a matter of unbolting stuff. I did NOT drop the skid plate. You can, and it makes it a bit easier, but I prefer not to remove the skid plate unless I have to. Don't jack it way up, or the engine fan can hit the fan shroud and or radiator.

Years of motor/gear oil leakage are fun to deal with:

The transmission mount that was in here was secured to the skid plate with studs. This makes it easier to get it aligned, but they also hang down further then bolt heads. Not that this Jeep is going rock crawling anytime soon, I just prefer bolts.


How the torque arm goes together:


New vs old transmission mount, the new one is probably 3/16" taller:



Scrambler Junkie
A few reference shots of the part #'s I found on the old transmission mount/torque arm bushings. Not sure if they are OEM or aftermarket:



When I pulled all the transmission mount parts off, I made an important discovery: The transmission mount bolt closest to the torque arm was completely missing!! This was probably the biggest cause of my power train movement issues. In the picture below, left to right: big hole for torque arm mount/bolt that holds steel plate to transmission foot/missing transmission mount to transmission foot bolt/and outer transmission mount bolt.


Picture of how it all goes together, note that the torque arm stud looks short:


What I do, and I am not saying it is correct, but I have done this with my red Scrambler with over 40,000 miles on it: I shim the torque arm stud with washers to keep it tight between the skid plate/metal bracket. This takes some trial and error to get it tight. I do not like how the factory configuration allows so much slop. The way I do it, this torque arm mount is like another smaller transmission mount, and keeps the power train from excessively "torquing over". Again, not saying this is "correct", just how I do it.


With the transmission/torque arm mounts installed, I moved forward to the motor mounts. Again, I used a bottle jack under the oil pan, and changed one side at a time. Again, do not jack too high or you will break stuff. I did the passenger side first. I found it easiest to remove the upper motor mount bracket from the block, too. This gave me enough room to get everything removed/reinstalled without jacking the engine up so high that the fan would jam into the shroud.


Old vs new:


And again, don't do what I do and forget to install these steel plates between the top of the motor mount and the bottom of the block mounted brackets. Pretty sure they are necessary due to the shape of the bottoms of the block mounted motor mount brackets. Nothing like thinking you are finished and see one of these plates on the ground LOL.


One neat thing on the driver side: besides the grounding strap, this Jeep still had this heat shield to protect the driver side motor mount from the exhaust pipe heat. I have not ever found one of these before on any of my Jeeps. I will take a picture of it installed and post a picture later.


So, after having to spin the transmission mount around, and redo the driver side engine mount because I forgot the steel plate, finished.

Will need to wait for a break in the rain for a test drive.

As for the poly mounts, I always hear people talking about how much harder they are then rubber. Probably true. BUT, the rubber engine/transmission mounts that came off of this thing are rock hard, harder then the poly!!!!

As for vibrations, my red/green Scramblers are as smooth as a new car, no weird power train vibrations transmitted through the poly mounts. I would not mind trying rubber mounts, IF anyone made good quality replacements. The last rubber transmission mount I used lasted two days on the dunes in Michigan!!

Again, your results may vary :twocents:


Scrambler Junkie
I had mentioned earlier, that even after all my careful work, my plastic valve cover started leaking from the back corner. Fun.

So, start with all this crap in the way:


Front stuff to be removed - fuel line, vacuum line, upper radiator hose, heater hose, pcv valve and hose:


Much more in the rear - heater hose, pulse air hose, more vacuum lines, pcv intake hose, valve cover mounted solenoid trio, 10"/4" vacuum switch on fire wall:


And, air cleaner/associated wire pugs and vacuum hoses, serpentine belt idler pulley assembly:


When I removed the cover the first time, the RTV seal was at least 10 years old. This time, maybe a month.

Well, the cover would not break free from the head. I tapped on it, tried to get a thin scraper blade to break the seal, no bueno.

I eventually started smacking the valve cover, HARD, with a sand filled rubber mallet. Would not budge. Instead, the plastic cover broke:


I hated to break it, I was actually going to try to re-seal it. Once it broke, game over. Even with "the gloves off", this damn thing would not come off. I tried to pry it off, just broke off more plastic:


Finally got an edge up, used a big pry bar, just broke the cover more, the seal would not break!!!


Yes, the cover is cracking in half, the seal will NOT break free!!!


Got half of it off, unbelievable.


Finally got the other half mostly off, and still had a big chunk stuck to the head!!!!!!!!!!


The thing that sucks - 98% of this cover was perfectly glued down, no way it was leaking. The plastic on the OEM covers is actually pretty damn tough. What is amazing, the RTV bond was stronger then the plastic. All my prep work paid off, obviously, but I missed a spot, so all for nothing.

I did not want to destroy the OEM valve cover, but there was no other way to remove it. Sucks.


Scrambler Junkie
Like I mentioned above, 98% of the seal must have been perfect. Hard to judge after prying the cover off, but you can tell I had a good bead/seal:



The back end near the firewall, where it was leaking, does not look good, you can actually see oil in the RTV:


And the rear cylinder head:


In the picture above, you can see where there is no seal around the outside of the bolt hole, and a thin gap/cut in the seal right above the rear bolt hole. I am assuming that is where it was leaking from.

Anyway, no sense crying over spilled milk. It just sucks that I was so close, yet so far away. But, maybe this proves you can get the plastic valve cover to seal up with RTV, I just wasn't careful enough :shrug::twocents::(


Picture cravin' AK Postal nut
Staff member
SOA Member
Like I mentioned above, 98% of the seal must have been perfect. Hard to judge after prying the cover off, but you can tell I had a good bead/seal:

View attachment 80087

View attachment 80088

The back end near the firewall, where it was leaking, does not look good, you can actually see oil in the RTV:

View attachment 80090

And the rear cylinder head:

View attachment 80092

In the picture above, you can see where there is no seal around the outside of the bolt hole, and a thin gap/cut in the seal right above the rear bolt hole. I am assuming that is where it was leaking from.

Anyway, no sense crying over spilled milk. It just sucks that I was so close, yet so far away. But, maybe this proves you can get the plastic valve cover to seal up with RTV, I just wasn't careful enough :shrug::twocents::(
:eek: Not quite. IMO, it proves the plastic is never worth reinstalling. Suppose it didn't ever leak but you needed to get in there for maintenance work. You would have had to break it just the same. That's not acceptable to me :shrug:

Totally admire the idea and all the careful work but there's got to be a limit.


Scrambler Junkie
Two hours of scraping/sanding/wiping down, and picking out pieces of RTV/plastic from the cylinder head/rocker arms, ready for a new cover:


I am going to install one of the ubiquitous "Made in China" aluminum valve covers, the type that says "4.2". I was going to spend more for one of the "Mopar approved" "Jeep" stamped valve covers, till I realized that they are made in China, too :(

Anyway, I have had good luck with the cast aluminum "4.2" valve covers in the past, hope my luck holds out :fingerscrossed: I had over 35,000 leak free miles on my Red Scrambler valve cover, right up till a piston skirt cracked and I swapped in 4.0.

Anyway, I'll post some more information/pictures if anyone is interested.

That's it for now :wave: