Seeking Advise: Carburetor/Timing/Vacuum Advance

[Ophale]

Aloha,

I have a 1981 Wagoneer with a 4.2L engine and 4 speed manual that I was given a few months ago. I been ticking away a bunch of issues when I have a chance but have been stuck on getting the Jeep to run smoothly and not backfire.

The jeep is not factory original with the prior owner making various modifications. The Jeep has a weber carburetor and a bunch of deleted vacuum lines. I have read various forums to try and understand the best configuration for the 4.2L with a weber. I'm currently configured like this as suggested from Neuner from the Jeep CJ Forum. https://www.jeep-cj.com/forums/f2/we...ed-help-22159/







This is what I'm observing, when I have the jeep running with the port vacuum plug and the vacuum advance open to atm pressure, the jeep runs fine at idle, but backfires when you have load or give it gas without load. If add the vacuum advance line from the port vacuum on the carburetor, I see the vacuum advance lever on the distributer oscillate back and forth and the engine runs like crap. I placed a vacuum gauge on the line and I see the vacuum pressure oscillate from the carburetor. I'm not sure what this means...

The timing has been set during all of these experiments at 8 to 10 degree retarded at an unknown rpm (i don't have a RPM gauge). I have backed off the idle screw to a point where it is almost stalling and then turned back a little bit until it sounds better as my start point to set the timing. I'm new to all this, and I'm wondering what is the best way to measure rpm when you don't have a tach in the jeep?

Finally, I feel I'm at a crossroads with this jeep. If it was you, would it make sense to spend the money and install a fuel injection system or to rebuild or repurchase the weber carburetor? The jeep was free, but I have a lot of body work ahead of me and other investments to make it into a daily driver. I wondering if there is a cheap way to get the jeep reliable for cheap by approaching things by taking it to the bare minimum to make things run. Since it is 1981, I believe it does not have the more complicated emission control systems. So what would be the bare minimum set up just to get it reliable without backfiring under load?

All the help you can provide will be greatly appreciated!

Best,

[babywag]

Sounds to me like a mechanical issue not a carburetor/fuel issue.
Verify all cylinders are firing?
Verify plug wires installed correctly?

I’d also do a compression test, and a leakdown test before spending any $ on a carb. or parts.

[Ophale]

Babywag,

Thanks for the suggestions!

Installed new plugs and wires a month ago. I will confirm everything is correct and look at the plugs to make sure they look Ok.

I will need to find the equipment and instructions to preform a compression and leak down test.

Best,

[440sixpack]

While it's idling slowly cover the air horn with a rag and see if it speeds up or wants to die. you kneed to know if you have vacuum leaks before you get too deep into tuning.


Running too lean or really weak spark can cause your symptoms.

[joe]

I'm a big fan of the 32/36 Weber on a 258. Infinitely tunable for for any conditions needed...but... that also makes'em easily screwupable if diving in blindly just twisting replacing stuff. A big factor of a Weber swap is the quality/condition of the adapter used to bolt it to your manifold. Be a good/easy place to check for a major vacuum leak. Otherwise my personal rule before tuning ANY carb is insure your entire ignition system is 100% up to spec before tweaking the carb. No idea what the PO did or bought but if the 32/36 was designed for a 258 and not say an MGB(?) new it should work great right out of the box "if" everything else is in spec. In the past using a 32/36 on a 258's I've never had to tweak the stock ign timing for normal on/off pavement use. Go back to basics and "know" what condition/tune the motor is in before you blame or fubar the Weber. The boon of all used rigs is the head banging drill of sorting out why/what the PO did.

[Ophale]

While it's idling slowly cover the air horn with a rag and see if it speeds up or wants to die. you kneed to know if you have vacuum leaks before you get too deep into tuning.


Running too lean or really weak spark can cause your symptoms.

Great info! I will put a sock in it (pun intended)... I've been suspecting a vacuum leak at the adapter plates. There tends to be water condensing at the base (adaptor plate) of the carburator on the fire wall side but the front side is dry. Either the plates are not mounted correctly or the gasket needs to be replaced. That may be the source of the air leak at the base of the carburetor.

I'll run the suggested test first and let the forum know what I find out.

[Ophale]

I'm a big fan of the 32/36 Weber on a 258. Infinitely tunable for for any conditions needed...but... that also makes'em easily screwupable if diving in blindly just twisting replacing stuff. A big factor of a Weber swap is the quality/condition of the adapter used to bolt it to your manifold. Be a good/easy place to check for a major vacuum leak. Otherwise my personal rule before tuning ANY carb is insure your entire ignition system is 100% up to spec before tweaking the carb. No idea what the PO did or bought but if the 32/36 was designed for a 258 and not say an MGB(?) new it should work great right out of the box "if" everything else is in spec. In the past using a 32/36 on a 258's I've never had to tweak the stock ign timing for normal on/off pavement use. Go back to basics and "know" what condition/tune the motor is in before you blame or fubar the Weber. The boon of all used rigs is the head banging drill of sorting out why/what the PO did.

Yes, I have no idea what the previous owner(s) did. I believe the adaptor is the weber adaptor that came with the kit. That said, my goal is to get it to run reliably with the least amount of $ investment initially. I'm glad to hear you have had success with the weber! I'm green at this, so it is the first time for me to muck around with a carburetor. I'm a chemical engineer with little formal mechanical skills. That said, I usually can figure things out, it just takes me longer than the pros. Forums in general speed up the process for me as there are a lot of great people out there, like you and others, who are willing to help with a problem that they have solved in the past.

I will find out if the Weber is actually a 32/36. Perhaps I can find a lot or manufacture number on the carburetor and confirm. I watched a few videos that basically say you need to start out with the air/fuel mixture screw and idle screw at 2 complete rotations from all the way in. I may take the Carburetor off to make sure it is mounted properly (as explained in 440sixpack response). Are there other things I should look for while the carburetor is off?

It's an old Wagoneer that needs some love to get it back on the road. It was operational 5 years ago, since then it sat at a coffee farm in Captain Cook, Hawaii with little attention. It needed to go to the recycler or be rehabbed. I got it for free. I don't know if it is worth it or not being a basic 6 cylinder with a manual transmission. That said, I like it and would like to fix it up (learn to do some basic body work on it, be creative and upgrade the interior to flannel and wood, and re-paint it light green with a 10 ft. quality job) so it could be a respectable daily driver. However, if the engine is toast, it may not be worth it. I have the skills to do basic maintenance on vehicles to more difficult repairs (replacing a clutch in a mini copper). I see the Wagoneer as an opportunity to learn other skills! If I get it to the point that it is reliable and do a few fun upgrades, I really don't care if I loose money on it, as I will gain experience that will be more valuable to me than the lost money on the investment when I sell it in the future.

[nograin]

Aloha,
This is what I'm observing, when I have the jeep running with the port vacuum plug and the vacuum advance open to atm pressure, the jeep runs fine at idle, but backfires when you have load or give it gas without load.

If its backfiring through the carb, the timing is too early. Its really the only thing that can set off the fuel and hav eit come back into the intake. Well, unless the valve isn't closing and then you have bigger issues.

If its backfiring in the exhaust its too late, either opening the ports too soon, or letting through too much unburned HC and hot gas that should have been pushing the cylinder down and cooling off in the process.

If add the vacuum advance line from the port vacuum on the carburetor, I see the vacuum advance lever on the distributer oscillate back and forth and the engine runs like crap. I placed a vacuum gauge on the line and I see the vacuum pressure oscillate from the carburetor. I'm not sure what this means...

Ported source of vacuum is a hole that should be just above the throttle when idling. It should see 0 to maybe 5"Hg on some.

Put a vacuum gage on an manifold source, and then check on the ported source. If its oscillating on the manifold source, then something is wrong.
If there is more than a couple of inches on the ported source, the throttle is too far open at idle.

Its possible the whole thing is just not setup close enough to get good consistant combustion at idle - hence the need for more thottle (higher idle speed)

The timing has been set during all of these experiments at 8 to 10 degree retarded at an unknown rpm (i don't have a RPM gauge). I have backed off the idle screw to a point where it is almost stalling and then turned back a little bit until it sounds better as my start point to set the timing. I'm new to all this, and I'm wondering what is the best way to measure rpm when you don't have a tach in the jeep?

Retard timing was only used as an initial on some smogged engines. To get away with that requires an appropriate carb with idle solenoid and related changes. Glancing at an '82 FSM, looks like the 6 was spec'd at 1600 rpm to have 15* Before TDC. And by subtracting the advance at 2000 rpm, timing at curb idle is probably around 2-5* BTC.



You need a diagnotic tach. Usually found as a Tach/Dwell on one meter.
Also get a timing light, and a vac/pressure gage, plus some golf tees.
You MUST get the timing correct before expecting any measure of success on the fueling.

Generally, a non-smogged (pre-68) engine used more initial advance and then needed less centrifical advance. At driving speeds the resultant timing was almost the same. This is a generalization. Camshaft changes, EGR and some other things mean we can't compare directly a mid 60s engine to its mid 70s or 80s equalivalent.

Finally, I feel I'm at a crossroads with this jeep. If it was you, would it make sense to spend the money and install a fuel injection system or to rebuild or repurchase the weber carburetor? The jeep was free, but I have a lot of body work ahead of me and other investments to make it into a daily driver. I wondering if there is a cheap way to get the jeep reliable for cheap by approaching things by taking it to the bare minimum to make things run. Since it is 1981, I believe it does not have the more complicated emission control systems. So what would be the bare minimum set up just to get it reliable without backfiring under load?

All the help you can provide will be greatly appreciated!

Best,

The only reason I'd consider EFI would be to do the crazy things needed to meet emmissions. An '81, especially a straight 6, had lots of emmissions controls as part of the package. Most of the basic emmissions controls were handled by vacuum and temperature switches. But sixes also got some electronic controls by 84. Those add another level of complication and difficulty.

I'd take stock of what emmissions controls the engine had, still has, and what it will need.

If stickers under the hood are missing. Look for the closest ones at Tom Collins Ol' Jeep website.

http://oljeep.com/index.html

There's an '80 diagram, and better yet, a full '81 shop manual.
I'm not saying you have to use all of the original emissions systems, but when cutomizing, need to know what was there and what's still hooked up.

Buying a 'rebuilt' or 'reman' carb from a parts store, or anywhere, often gets you garbage. If it needs new gaskets, or has old fuel that clogged passages etc, clean it yourself and replace the gaskets.

Get the timing correct for idle, readjust the fuel to match, then see where you are at.

[joe]

Don't be put off cause it just has the 258 and manual trans. The 258 is a solid reliable motor and plenty of power to move a Wag around and easy to rebuild if needed. Also get's better mpg's than the 360. Be glad it's an 81 and not 83-87. 83+ have an insane amount of elec/vac switches and plumbing. Since you're starting from scratch with a non-runner I highly suggest getting the AMC factory TSM (shop manual) for your year. A decent Weber book is "Weber Carburetors" by Pat Braden published by HPBooks. Amazon probably sells it. Since yours has been sitting idle for 5 years odds are good the carb needs a good cleaning especially if in HI your running the corn sqweezins government gas(ethanol). Hope your free 81 is worth rescuing. Enjoy.
edit: for a model number look at the short end of the base. There will be a machined boss or two that will have the model number stamped there. Likely something like 32 36 DGV.

[Ophale]

It has been a busy two weeks... Just had an opportunity to pull the weber off the engine to look at the part number. What I can read, I have a Weber 32 36 DGAV33B1 046 11 (see picture below).



I'm not sure if this is the weber that is specified for the 4.2L Jeep. So I looked inside at the installed jets. This is what I found:

Idle jet: primary 75, secondary 60

Main jet: primary 145, secondary 145

Air corrector jet: primary 160, secondary 110

Can't seem to pull the emulsion tube.

I also read that I need to have a fuel pressure regulator (set at ~3 psi).

Based what I've read, I'm not sure if this is where I need to be on the jets. I'm beginning to wonder if it makes more sense to just purchase a new carb that is set up for the 4.2L Jeep?

I also took the EGR valve off and found out that it was not connected to the exhaust or could hold vacuum. The EGR valve was plugged at the bottom with a threaded plug and a similar threaded plug was in the exhaust header just before the down pipe. Found gas in the EGR system...

Thoughts on what to do next? Rebuild kit and a jet kit (~$100) or new carburetor ~$275.

I also was wondering about the electronic choke and how it works. It there seems to be one connection to it. Where does it get its signal from (temperature sensor) and is it a voltage or an amp signal? Thinking about changing it to a manual choke, as that might be more convenient for me.

Thank you for all your help!

Aloha,

[Ophale]

It's been some time... made progress... but not at the promise land yet...

Aloha!

Since my last help post I've made some progress with couple of issues on the Wagoneer. However, I'm still having issues with tuning the Weber.

Progress that I've made thus far:

I replaced the distributor with an HEI
I replaced the old weber with brand new one 32/36
I replaced the power steering pump
I replaced the starter
I replace the solenoid
I replaced EGR Valve (not hooked up to vacuum or exhaust, have plug where exhaust pipe connection would be on the manifold)

The issue I'm having is with the Weber still: I've been able to set the idle speed screw to no more than 1.5 turns max (as described in the manual and visually confirmed that the progression holes are above the throttle plates). The mixture screw is 2 turns out. I've removed all the vacuum lines from the weber with the exception of the manifold vacuum to the power steering and the S port vacuum to the HEI distributor.

The Wagoneer starts with the choke engaged, but once I warm things up and rev the engine up it stalls at idle. Timing is set at 10 deg BTDC. I've taken off the vacuum advance and have a vacuum gauge on the s port. The vacuum reading is close to zero before it stalls at idle. I've adjusted the mixture screw to lean it out and make it richer, but I can't get it to idle... RPM is about 500 with the choke engaged, 10 deg BTDC, vacuum on the s port at 15" Hg. Exhaust smells rich, plugs are black but not oily. I also sprayed carb cleaner, no change in engine speed... around carb mounting plates or any place where there is a vacuum line.

What would you do next?

Thanks in advance for any suggestions!

[wiley-moeracing]

you may have an intake leak at the head, try spraying the mounting flanges top and bottom to see if you pick up rpm.

[Ophale]

Thanks wiley-moeracing!

Just before I gave up for the day, I started tightening down the intake bolts. I believe I'm on the same wave length as your thinking. I found the front two bolts a bit loose but got into clearance problems with my socket wrench as I moved into the engine bay. I also noticed a vacuum line (I believe it's a vacuum line...) that connects to the back of he intake manifold and goes to a black cylinder mounted above the engine on the fire wall. What is this, and could it be the source of the vacuum leak... Any other potential sources of vacuum leaks to look for on the intake manifold, like ports that may have a sensor or connection I should check to see if it is missing or broken?

Aloha,

[wiley-moeracing]

try using some carb cleaner and spray all around the ports on the intake( underside also) to check for your vacuum leak, the hose on the back of the manifold I am not sure about unless you can post a pic.

[Ophale]

Had a few hours free Friday to work on the Wagoneer. Sprayed Carb cleaner in and around the intake manifold, carburetor, and various ports (emptied a can and half). No evidence of a vacuum leak. At this point the only vacuum connection I have on the Carb is to the fuel reservoir and the brakes.

I may open up the carb to reset the float...

Still looking for ideas.

Aloha