Runs kind of rough, wants to stall when given throttle?

Hi,

I'm sorry for the delay in answering. We have a tech on here that knows these vehicles inside and out. I was hoping he would answer it for you, but since he didn't yet, I figured I better. LOL

Okay, first I need to understand something. Do you mean when you removed the vacuum from the EGR, it ran better? I ask because that should have made it run worse unless the engine is getting too much fuel and the added air intake allowed it to lean out a bit.

Let me know about that.

Now, as far as vacuum advance is concerned, it really is somewhat simple. The vacuum advance is a component of the ignition system that plays a crucial role in engine performance and fuel efficiency.

The vacuum advance is a part of the distributor, which is responsible for distributing the high-voltage current from the ignition coil to each spark plug at the right moment to ignite the air-fuel mixture in the engine cylinders. The purpose of the vacuum advance is to optimize the ignition timing based on engine load and operating conditions.

Here's how it works:

When the engine is under light load or at idle, there is relatively low air intake into the cylinders. In such situations, the air-fuel mixture burns more slowly, and the flame front takes longer to travel across the combustion chamber. Therefore, it's beneficial to initiate the spark plug firing slightly earlier than when the engine is under heavy load or high RPM.

The vacuum advance is connected to a port on the intake manifold, which is subjected to changes in pressure depending on the engine's load and RPM. At low engine loads, the manifold vacuum is high, while at higher engine loads, it decreases.

The vacuum advance mechanism uses this manifold vacuum to advance the ignition timing. When the vacuum is high (low engine load), it causes the distributor's internal mechanism to rotate the distributor shaft slightly, advancing the spark timing. As a result, the spark plugs fire earlier than they would without the vacuum advance, improving fuel efficiency and idle smoothness.

I hope that helps. Let me know exactly what your Jeep is doing, and I'll try my best to help.

Take care,

joe

Here’s a video with better description.

Hi,

The video didn't fully upload. It lasted about 4 seconds. LOL Could you try to upload it again?

Joe

I uploaded it again.

I'll give you some explanations of some of your concerns.

If you have to pass emissions tests in your region, you may have to put everything back on like it was originally.

Where I'm at, we are not tested, Jeeps can run well with the bare minimum hoses and equipment.

I'm running a 1977 CJ-5 with a 258.

My 258 came out of an AMC Hornet and I built over many months time, as my fundage allowed exactly like an OEM 1979 Jeep CJ. The only "extra" I did was to add a High Volume oil pump.

(one barrel carburetor 258s use a different cam than 2 barrel 258s)

"Mr. Jeep" is my daily driver, once the engine was complete, I did a 6 hour swap in my Dad's carport to include a clutch kit.

It was as if he was never down at all!

This was in 1996, engine-wise, all is still wonderful!

Other, basically, "bolt on mods" along the way are a 4 barrel 390 Holley, and a 4 barrel Offenhauser intake, Headers, I replaced the Prestolite ignition

set up (like yours) with Duraspark like the '79s came out with, and a 21gallon poly fuel tank.

Other "Fads" and supposed "Upgrades", like a weber 32/36 carb never improved mine at all (but that's my opinions!)

I'm always "listening for" more real/ truthful MPGs and I don't have/want to have a Race Car or a Log Skidder---I have 2 Jeeps!!!!.

I get 18 MPG on the highway, longer range, 21 Hg on a vacuum gauge at idle, Oil pressure is 30-70 PSI, capable of "Smart" offroading!

I don't run big tires, their bigger than the originals, but are now days thought to be small (Mine are 235/75/R15)!

So, I've been daily drivin' this engine for 32 years.

Lets start out with your PCV system!

Use the correct PCV valve for your year--in the front hole--with a good snug grommet. The back hole is "Fresh Air" for the PCV (not EGR) it should have tight grommet and a fully open elbow extracting air from your breather.

(the best place, as you normally change the filter element and would not worry with changing a separate one).

Your carburetor kinda sucks the bad combustion gases out of the engine, that replenishes clean air inside, and the carburetor was designed to use that "extra air or controlled vacuum leak (if you will)" to mix with fuel so your engine can be tuned properly at idle.

Depriving that air makes it nearly impossible to tune correctly. (never use a 2nd PCV valve as an elbow at the back, it "checks" (and blocks/ closes) if air is drawn backwards through it.

My next posting will be about your vacuum lines and vacuum operated stuff.

Emissions tests???

Do you have a return line to the fuel tank??

Most of what I'm posting is 1960s-1970s basic car etiquette!

---The Medic

Hey, thanks for the detailed response! I’m not looking to pass emissions as I live in Michigan. I just want the Jeep to run good. I do have the proper PCV valve tubes, I had them off just trying to experiment with the running issues.

I do not have a return line to the fuel tank. Also, so what you’re saying is to not block off the EGR valve? I made a cover for it today to see if it made any difference, it didn’t.

Also moved around the distributor a little bit while running to see if maybe that would make a difference, still none. I did notice the difference in run quality but no difference to my throttle issue.

I have noticed that the cart YF is in pretty mint condition on my Jeep, makes me think it was new old stock or something. I’m wondering if maybe it needs different jets.

I pulled the plug today and purchased a Weber 38 kit. If that magically fixes things then I guess I’ll have my answer lol.

I was hatched up that way at K.I. Sawyer Air Force Base (Marquette)

Let's not get carried away with the weber yet, it might be really involved to tune it.

In your video, I thought, that You thought, the back hole in the valve cover was something to do with the EGR??? The back hole is for fresh air (I explained that in the last post)

Blocking the EGR is fine! If you installed headers, you would have to do it.

We need to make sure there are no vacuum leaks anywhere---which includes uncapped (sucking) ports!

Without power brakes, only 2 vacuum lines are needed to run the engine.

The PCV

and

The vacuum advance to the distributor

I have an extra one going to an "in dash" vacuum gauge.

Without a few tuning tools, it's nearly impossible to "wing it by ear".

Your PCV valve needs to be fed by Manifold Vacuum from a larger port.

This will be a Port anywhere "Below" the throttle plates in the carburetor, it will constantly suck air. It can be used from the intake manifold, not just the carburetor.

The distributor "normally" uses ported vacuum, some folks think that manifold vacuum is better. Lets do ported for now!

Ported vacuum is generated "Above" the throttle plates in the carburetor.

It is vacuum that "comes alive" as you increase the engine speed (a vacuum gauge connected to the port would easily show this happening.
Usually just cracking the throttle plates open slightly will make a port begin to suck.

Everybody else needs a vacuum cap or a piece of tight fuel line and a bolt
to eliminate any sorta vacuum leak!

This link might also help explain setting things up similar with yours.
https://www.2carpros.com/questions/jeep-cj7-1985-jeep-cj7-stalls-when-hot

On the front of your carburetor, on the right, you have your fuel line feed coming in. Beside that, on the left, is an Open port (DO NOT CAP IT!) It is your "Bowl Vent", Normally it would hook to a charcoal canister.

No canister? It still needs to breathe! I have a pic of a Carter BBD and a similar way of how you can do yours using a sacrificial fuel filter hooked to nothing.

The Medic

Small world lol. I live in Marquette and for the next few days I will actually work on KI. How’d you know?

Anyway, yeah, I mixed that up in the video about the EGR.

So, the PCV valve needs to go below the throttle in the carb? It was situated on the top of the carb when I got it. There are no connections on the intake I can use but there is one large one at the bottom of the carb. It was plugged with a hose and a bolt when I got the Jeep. I thought that would be a fuel return line.

I’ll have to reread your comment when I’m next to the Jeep to try to figure out where to put the vent and filter in place of the charcoal canister.

I’m not entirely sure that there’s suction from my pvc. I know there’s positive flow blowing out of the back end of the valve cover, like flowing out, not in.

Hi,

I would rather CJ answer this, but if I mess up, he will let me know. LOL

As far as the PCV, the valve should be in the valve cover and the other end does go to the bottom of the carb. The hose you mentioned as being plugged is the likely vacuum source.

Let us know if that helps.

Take care,

Joe

Thanks for replying! I’ve learned a little bit more about my Jeep since I’ve asked that question. I’ve purchased a timing light, gave up (for now) on the carburetor and purchased a new Weber 38. I also purchased a vacuum and fuel pressure gauge.

I’ll install that new carburetor, then check and set my timing, check vacuum advance and gas pressure and make sure that’s all kosher.

Hi,

Thanks for the update. It sounds like you have been busy. When you have a chance, let us know how things turn out for you or if we can help in any way.

Take care,

Joe