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I would start with checking the timing.
 
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Quick question. Is your vacuum advance hooked up to ported or intake manifold vacuum? It should be to manifold vacuum. Period. No debate. If it is to ported vacuum it is wrong.

Yes. You could have a worn distributor (I hate the word dizzy, it is not called that in the professional world, it is a redneck internet I don't know how one really works term. This is just unjustified rant from me but I have never called one that nor has any decent tech I have ever worked with. DO NOT EVER USE THAT TERM AROUND ME AGAIN. JK. People who call them that just sound dumb though. If you want to shorten the word call it a dist. :RANTOFF:)

The shaft bushings may be worn but that will generally be seen with a timing light at idle and the marks are not steady on the pointer. You will see it jump up and down rather than hold steady at 8 degrees. Another thing is the centrifical advance may be sticking or binding at times. With your vacuum advance disconnected you can rev your motor up to about 3000 RPMs gradually while watching the timing marks. It should smoothly advance up to somewhere around 30 degrees or so. It needs to be pretty smooth and consistent if you do it over and over again. The same is true for the vacuum advance. It should provide true and consistent movement when tested with timing light. That can be done at idle with a vacuum pump hooked to the vacuum advance.

One last thought and this is one can be tricky is carbon buildup in cylinders can hold in heat and stay cherry red and ignite fuel upon entry into the cylinder rather than waiting for the ignition to fire it. This condition is pretty rare and sometimes not really explained how it happened. I would have to type a book on my theories of how it can happen. But anyways, this just popped its head up in a situation that I know of a couple of weeks ago. A very dear friend and fellow tech that I have worked along side of and respect the hell out of, he is an amazing engine builder and hot rod kind of guy ran into this on a vintage Mach 1. The car pinged no matter what. It had been messed with and messed with with no resolution. John (my buddy) advised the customer that this was really the last and only problem that could be the issue. This prognosis was made some time ago. The customer was reluctant to pull the heads then, kept driving it like it was. He sold the car for a very high price but when he went to get it ready to ship it ran like absolute crap. It had misfires on two adjacent cylinders which and low compression on both which indicates a blown head gasket in between those two cylinders. John tore the heads off and sure enough the gasket was blown where it was suspected but he also found that those two cylinders had the hardest carbon deposits on them known to man. I was not a simple cleanup, the stuff had to actually be chipped at and broken up. I was in the combustion chambers on the heads but really caked up on the pistons. He did the cleanup and reinstalled the heads and miraculously the spark knock was fixed and the Mach 1 ran like it never had before for the customer. BTW, the spark knock is what caused the head gasket to blow. Detonation is a *****.

Sometimes you can cure this without a teardown. The product I believe in the most is GM top engine cleaner. If you heat up an engine and rev it up to maybe 2000 RPMs and pull it in through a vacuum source til the motor runs rough and then get it to stall out by basically flooding it with the top engine cleaner and let it heat soak. for a good while to break down the carbon in the cylinder. Crank it up a couple of hours or so later and it will smoke like all get out. Run some more TEC through it. change the oil and see how it goes.

Trans fluid can do the same when used the same but not as effective. Sometimes running water though can steam clean it. These are both used in somewhat the same method as described for the top engine cleaner.

Be fully aware. You are pouring liquid into a motor that does not combust. It can hydrolock an engine and bend or break connecting rods for instance if you are not on top of your game. Use at your own risk.

Others may mention seafoam or other products. I have never tried them.

Hopefully this helps.
 

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You can call them a dizzy. Everyone else does. My rants are not always serious. I gave you a JK and a wink in that paragraph.

It is hard to say if that port is manifold or not but it is easy enough to tell. If it is ported, it will probably cure your problem to move it to manifold vacuum. It should be manifold vacuum though. I know that there is internet info that goes both ways but running ported provides vacuum and thus timing at the wrong time and does not provide more timing when it is really needed.
 
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If you are running a factory gauge I would not take the readings as gospel.

Yes. The vacuum advance being plugged in at idle should pull your advance way up off the scale. Somebody on the forum keeps mentioning that the "newer" timing lights or something like that are evil basically speaking of a light that you can dial back degrees. I have both kinds of timing lights. Taking away my dial advance timing light which was claimed to be evil would be like removing my right nut. I would not function well after that. When that timing mark moves past the markings by a long shot, I can dial it and bring it back to a mark and read the amount of degrees I brought it back. These lights are an absolute must for anybody that really knows how to curve a distributor and tailor it to a specific engine.

I have never worked on one of these Weber carbs. Sorry. I cannot answer specific questions about them.

A light bulb turned on though looking back at your OP. The 4.2L has an EGR valve. Do you still have an EGR valve and does it function? Forget all the EGR myths that the net brings. You are recirculating a free source of inert gasses to fill the combustion chambers at times when max combustion is not needed to motivate you down the road.. Inert gasses do not need additional fuel added to them vs non EGR so you can get the same power with less fuel. It takes a book to explain EGR operation, benefits, and even power losses. There are tons of myths and misunderstandings. But if a spark curve is set up to utilize EGR then eliminating it can cause issues. EGR does reduce cylinder temperatures and reduce pinging. Crazy. Hot exhaust gasses can cool cylinders. Who woulda thunk?

Seriously. Do you still have an EGR and does it function?
 

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Have you verified if your vacuum advance is ported or manifold vacuum? You can tell it by putting your finger over the hose at idle or using a vacuum gauge.

Sometimes when I share theory and knowledge it sends people off the deep end. I tend to ramble and do not convey the simple parts of my message well.

Finding an advance timing light is a bonus, and arguably a necessity if you will continue to run carbs and distributors but many of them are becoming vintage and way to much money. There are other means.

Your EGR is blocked off for sure. Lets not reinvent the wheel. Many people have eliminated it with success. It can help with forgiveness for spark knock at cruising speeds though.

Another thought is Harmonic balancers can slip over the years. There is a hub that mounts to the crankshaft, then a rubber insulator, and then the outer wheel that has the timing mark. Inertia over time and rubber rot can make your timing marks fall backwards. It can be verified by checking true TDC of your engine. A dial indicator is best, but sticking a screwdriver in the spark plug hole and really paying close attention to when the piston goes up and then down and has the degree or two where it is at the top. Find that and see if your balancer mark points to zero.
 

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Another thought is Harmonic balancers can slip over the years. There is a hub that mounts to the crankshaft, then a rubber insulator, and then the outer wheel that has the timing mark. Inertia over time and rubber rot can make your timing marks fall backwards. It can be verified by checking true TDC of your engine. A dial indicator is best, but sticking a screwdriver in the spark plug hole and really paying close attention to when the piston goes up and then down and has the degree or two where it is at the top. Find that and see if your balancer mark points to zero.
I really would check the balancer marks at true TDC that is verified by piston movement. You said at one time your timing was set to 4 degrees and now it was back to 2 degrees.

If you decide to go the HEI route, you can find distributors that are adjustable as far as both the mechanical and vacuum so you can tailor its curve.

Have you verified that your vacuum port you are plugged into on the carb is manifold vacuum and not ported? Manifold vacuum will be 18" or so at idle, ported will be zero at idle and the signal will get stronger as the throttle is opened.
 

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If it is pulling full vacuum at idle, it is manifold vacuum. Carbs can and do offer both types of ports on them. With me not really being familiar with a Weber carb I just was not sure which way that port on yours is.

I really need to find a cheap Weber to take apart and study and become familiar with it. I am a Carb guy from way back and really understand them very well. They all have the same basic principles to operate but how it is executed from one brand to another can be very different.
 

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Look at this picture from an earlier post of yours. . To the lower left you have a vacuum line that goes into the intake manifold. It should be a rubber hose, then a check valve and a plastic vacuum line connected to it. What I would do is put a longer piece of rubber line with a tee between the intake port and the check valve and plug the distributor vacuum line to that tee. That way there is no doubt whatsoever that you have the correct vacuum signal to the distributor.
 

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I did not say for you to add a check valve. You misunderstood my post. Your engine has a manifold vacuum source that has the port into the intake which has a rubber hose attached to it, then a check valve and then a plastic vacuum line.
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I really thought that I described it very thoroughly, but this should help.

The green arrow points to the manifold vacuum port. The Blue arrow points to the check valve that you already have. The red circle is where you need to install a tee. So, the rubber vacuum line in the red circle..... This is what you are going to replace with a new piece of line and a tee. Get a new piece of vacuum line, of the same ID and a tee that fits it. You are going to need a slightly longer piece of line than you have. Put a piece of rubber line to the intake port. (green arrow) Put your tee into that vacuum line. Put another piece of vacuum line on the upper side of your tee. And then put your check valve (blue arrow) into that line on the upper side of the tee.

You are simply replacing the rubber hose in the red circle with two pieces of vacuum line and a tee.

Now move your distributor vacuum line from your carb to the Tee and cap off the port at the carb. This removes all doubt about you having intake manifold vacuum to your distributor that is not influenced by the venturis on the carb at all.

YOU ABSOLUTELY DO NOT WANT TO INSTALL THE TEE ABOVE THE CHECK VALVE. IT NEEDS TO GO MANIFOLD PORT, RUBBER, TEE, RUBBER AND THEN CHECK VALVE.

And yes. When you do this your vacuum advance will pull to full advance at idle. That is what you want. That is normal. That does not indicate a worn distributor.

Your vacuum advance provides full advance under two conditions, Idle and cruising with a very light load on the engine such as level road or even going downhill. When you are at cruising speed and start to go up a hill or grade, your engine load increases. When the engine load increases, the motor will ping easier but your manifold vacuum will drop because the engine is under load. Because the manifold vacuum drops in that condition, so will the signal to the vacuum advance. This means that your timing will back off correspondingly because the vacuum advance does not pull as far with less vacuum

I seemed to have confused you or you are reading too much of somebody else's material and confusing the two. I do not know.

The reason I suggested that you move your distributor vacuum connection to this point is your own posts that indicate that knock off vs real webers are inconsistent on what this vacuum port does and IMO it is too wishy washy and I do not believe that you have a vacuum gauge or totally understand engine vacuum under different operating conditions. This method removes all doubt.
 

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Wait until we get started on how vacuum is really a pressure differential and how it all effects fuel delivery also. LOL.

This is kind of random but yet this thread was leading me down the path of trying to figure out how to explain a few things about vacuum and I stumbled into a writing by MOTOR that states that ported vacuum can never exceed intake vacuum.

Guardair 79SG012 $58.29 Pistol Grip Syphon Spray Gun | Zoro.com

I will just drop this link here to prove that ported vacuum CAN exceed intake vacuum. There are things known as venturies and what they can do is cool.
 

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No. The link is something that you put an air pressure hose to and you squeeze the trigger and air pressure runs through it and believe me it is all pressurized but somehow the hose on it can siphon liquids up and add them to the pressurized air stream. It creates a low pressure/vacuum to siphon but yet it being totally pressurized debunks when MOTOR said that ported vacuum cannot be below manifold vacuum. I am just saying that there are venturi effects and different ways to use them that makes that totally not true in all situations.
 

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Thanks for the update. We love success stories. Congrats on seeing it through.

I wonder if the nutter bypass had been totally done. The ignition module did have the ability to change timing electronically. It had to in order to make a knock sensor work in the system. I will not even try to explain how it did it but lots of guys praise their results when changing over to an HEI.
 

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You got the pinging to go away and that is critical. That will destroy and engine by melting down pistons and valves. Like melt them like you took a torch to them. Bad news.

Your YJ must have pinged horribly because it is really difficult to hear a spark knock in one with a soft top or top off.

Now you can move on to your Jetting issues but quite honestly, most carbs are pretty close out of the box. A given amount of air needs a given amount of fuel. Too big of carb on an engine introduces some really bad and not tuneable issues. You have an arguably slightly undersized carb which should perform very well. Its limitation will be higher RPMs.

I would drive it a while and really honestly assess how it runs, how it smells, what the economy is and Jeeps do not have good economy. And last. Look at the plugs after a while to make sure that they are not sooted up.
 
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