Engine/Carb issues - 304 V8 4bbl

Let me first start off by saying that I am NO MECHANIC. I know how to put in the key and turn it, that's about it. I don't know how to adjust carbs, valves, etc. My skills are limited to bolt off/bolt on type stuff. I am willing to learn thoguh! So, keep that in mind!

I've got ~40k miles on the stock 304 in my '74 CJ-6. The original owner converted it to a 4 barrel off of a full size jeep. I was driving it the other day when the throttle got stuck on the floor, and it took a few seconds to unstick it, so the engine stayed rev'd up for about 5 seconds or so. Well, ever since then, the issues I had been having seem to have been amplified. Here is the breakdown.

Carb - Motorcraft 4 barrel off of FSJ. Fresh rebuild, but not dialed in.

Gas tank - Brand new, but fuel lines are original. Unsure of fuel pump. Not sure if there is crud in the lines.

Spark Plugs - Just changed them today, opened up gaps to ~ .037. Original plugs were gapped all over the place, and all 8 were covered in carbon and fuel.

Ignition - Converted to stock AMC '75 and up electronic ignition (is this a Duraspark setup?)

Symptoms:
1) Hard to start if it sits for more than a couple of days. Moreso than a typical carbureted vehicle, so I'm not just spoiled by fuel injected vehicles.
2) It's idle (once it settles in) is inconsistent. It always idles well, but sometimes it's at 1,000 rpm, others at 600 rpm. From day to day, not minute to minute. One day it idles at 1,000, the next day it could be different.
3) It's never liked a quick stab at the gas pedal, but now it's really bad. If I punch it, it will practically stall, then I let go and it jumps back to life. It's always done that, but ever since the throttle sticking that day, it's gotten worse, and now it will backfire right after the quick stab at the throttle. It's also backfired a couple of times through the exhaust, but mostly through the carb.
4) It likes squeezing the throttle just fine. It won't backfire, and it will steadily build the rpm's. It used to throw a lot of carbon, but that seems to be slowly going away.
5) With 33's and 3.73's, it's fairly high geared but I usually have to start out in granny (T-18 tranny w/granny low swapped in by PO) because it doesn't seem like it has enough power to start in second gear. The PO told me that it was a strong runner, and with the Meyer's cab removed, it was almost scary. I haven't seen that yet. It runs fine oncec rolling, but right off the bottom it doesn't like to get rolling.
6) While at idle, I started pulling plug wires off, and in some cases it was drastic, in other cases it seemed to make no difference. (is there a way to do this without getting shocked, cuz my motivation went south quickly after the first time!)

Any advice? I am currently shopping for a 360 and I want to put the Howell TBI setup on it. But I am looking at next summer at the earliest. In the meantime I want to get it running reliably so that I can start using it more and build some trust in it.

Thanks!
Agar

 

Update - Farted around with it some more today....the fresh plugs helped a little, but the symptoms are the same, just lessened. I was gonna change the plug wires, but local auto parts store didn't have any in stock. My buddy says he can test the current wires to see if they are good.

 

First I'm not a real mechanic. But I have worked on lots of stuff so take this for what it's worth.

I would start looking at electrical issues. I'd put a timing light on each spark plug to make the are all getting spark. This is much eaiser on you than pulling the plug wires on a running engine. You mightnot be gettins spark on some cylinders. But you might. You might be getting a weak spark that breaks down under load.

So make sure you are getting spark to all cylinders and let us know what you find out.

 

I would get a quality universal wire kit and cut them to length.

Is this a 4350 carb? They are well known for having warped carb tops. If you suspect the carburetor, take the top off and assess it with a straight edge.

The '75-77 electronic ignition is the Prestolite system. They were a ton of trouble, even when new - I would not put any money into that ignition system if it were mine. In 1978, Jeep went to Motorcraft ignition (aka Duraspark) which is much better.

 

Also, if you have a strong 304, I'd suggest you keep it and focus on other upgrades. Have you done a compression check? What's your oil pressure, hot idle and running? The 360 is a 304 with a larger bore and different heads - a very similar engine. 360s are popular now because they were in production into 1991 and there are more of them around than 304s. They do provide a comparatively cheap improvement in performance, I'd guess about the same as the increase in displacement. Despite that, I think a 304 in a CJ chassis should be plenty of engine for most drivers, and having more power on tap with a 360 will mean you're more likely to break something.

If you want bragging rights, go with a 401 ... that's a significant step up in performance from the 304/360. The 401 brings both much more power and better technology with it, plus higher resale value.

 

Thanks for all the great replies! My buddy should be coming over today or tomorrow so we can test the plug wires.

Not sure which Motorcraft Carb it is, and for that matter, I can't even guarantee that the ignition is the Prestolite or the Duraspark. It may be the Duraspark because the module was given to me from a fellow Jeeper and I believe it came out of a later model CJ. Either way, I need to chase that down. Quite frankly, I would love to swap it out for a DUI and be done with it.

Thaks for the input Tim! Your a virtual Wikipedia of Jeep know how, and I was hoping you'd respond!! I agree on the argument. There are a some reasons I want to go with a 360, right or wrong here they are:
1. I don't care about big power numbers, but I like the instant torque gain from the extra displacement. I would be happy with ~250 hp, but an extra 50-60 lb.ft. of torque would be a great gain. I also like torque gains from displacement as opposed to "builiding torque." Torque is largely a function of displacement, so building torque in a smaller engine seems to me like it would push it up the RPM range and make it less usable. I'm no expert, just my intuition....I know I'm talking to guys who know their stuff, so I am commenting moreso to give you guys my mindset.
2. I don't like spending bad money before good money. I definitely want EFI, and DUI eventually. The catalog shows two different part #'s for the EFI setup, one for the 304 and one for the 360. Basically, if I'm gonna spend the money on the bells and whistles, may as well stick the bells and whistles on something fresh and torquey.
3. The 360 is more plentiful, and some parts don't work on the 304 (Edelbrock heads for ex. due to valve clearance, or so I'm told)

Thanks again everyone! Keep 'em coming, cuz I have a feeling I'll be chasing these issues for a while. Gotta get the '6 to a place where I can trust it more so I can drive it more.....gotta let the world know that 6's did in fact exist!!!

 

Prestolite has a plastic vacuum advance can on the distributor. Duraspark is plated steel. The Duraspark can be made equivalent to the DUI with the TFI upgrade. It can even be used with the GM HEI module, which is also used by DUI.

Call Howell and ask about the difference from the 304 to the 360. I expect it's just a different chip, and that they would fix you up if you swapped to a 360.

The Howell stuff is good, but they do not support spark control AFAIK. With the GM HEI or the I suppose the DUI (basically the same thing), you can control the spark advance through the distributor module, just like GM does on their cars. If I went with the GM TBI, I would do the complete installation with spark control. This would require hacking the computer yourself, or using someone's kit that supports spark control. This also makes using the knock sensor possible in theory, but transferring knock sensors from one engine to a different engine may or may not work.

The valves are smaller on the 304 head than on a 360 head; the larger valves on the 360 head interfere with the cylinder bores on a 304. You can use 304 heads on a 360, but not vice-versa. The 401 head is the same as a 360 head.

 

I just checked the distributor and the vacuum advance is steel, with "Motorcraft" embossed on it. So, that solves the mystery of what I've got for an ignition....my apologies, I should have noted that before my initial post.

Remaining mystery, why does it stall if the gas is pushed too hard and why is it backfiring? Also, I forgot to mention that the mileage is horrible, definitely less than 10 mpg. I would give a better figure, but my speedo cable twisted on itself and snapped, so I have no odometer. That's just one of the many things on my list!!

 

Have you checked the accelerator pump? How about the secondary jets? Sound like it is not giving enough fuel when you crack open the throttle blades.

When you crack open the throttle the accel pump has to squirt enough fuel to make up for what doesn't come out of the main jets until the motor revs up enough to make enough vacuum to pull fuel through the jets. Crack open throttle, vacuum signal drops off, accel pump squirts motor revs up, vacuum back.

 

HEI and Edelbrock carb are a relatively inexpensive upgrade to the 304. My 304 seems to run strong and move the jeep along. I'm not a racer and don't expect more than 65 or so out of it, though.

 

I had thought of that, but to be honest, I'm waiting for my buddy to be free because carbs to me are part art, part science, and I am neither an artist or a scientist! Seriously, every attempt I've made in the past to tune a carb have been salvaged only by my note taking and being able to return things to where they started. I should have access to my buddy later this week. In the meantime I've pulled 2 straight 15 hour days at work, so it's been dark when I get home, and the rest of the week isn't looking any better.

I have had a chance to check some other things out....the carb doesn't seem to be leaking from the body or any other location, so I'm hoping it's not warped. My quick inspection however is by no means the final word on that subject. I'm also pretty sure the ignition is the Duraspark setup. I have a fresh fuel pump in my garage, so I am tempted to finish off my new fuel tank part of the project by freshening up the fuel lines, fuel pump, and fuel filter. Probably won't cure anything, but the old tank was pretty cruddy, so it couldn't hurt.

 

If you have a 4350 Motorcraft 4V, it has a unique spreadbore base design and nothing else will bolt to that manifold. You need to know what carburetor you have. Does your carburetor have a tag? Did you rebuild it, the PO, or a rebuilder? If it was rebuilt by the PO, I'd expect that's your problem. Can you take the carb off of the top of the engine? If so, look at the base pattern - square bore is 4300, spreadbore is 4350.

Also, since you have the Duraspark ignition, I would do the TFI upgrade now. This will give you an ignition that is equivalent to the GM HEI or DUI. There are lots of articles online if you search for "Duraspark TFI upgrade." This upgrade will replace your cap, wires, rotor and coil, so doing it now will cover the problems you're having with the wires now.

JMO - if I were going to go with the Howell kit, I'd do it now. You'll need a new manifold if you have a 4350 - you may as well get a 2V manifold, since all the TBI throttle bodies are 2V designs. If you have a 4300, you can buy an adapter for the squarebore pattern. Ask Howell what your upgrade path would be if you went to a 360 - I expect the only difference is the chip, and that they would work with you.

 

I've only now gotten a chance to get a closer look at the carb. I will take it off this weekend, but for now here's what I found to try and identify it.
1) It's got a tag on the front of it. It has the AMC logo stamped, with "4TA4 AA" stamped beneath that, and "B 4G 26" stamped beneath that in smaller letters.
2) The lower portion of the carb (the part that bolts to the manifold) appears to be made of aluminum while the upper portion is your typical brass colored. The base portion is not an adaptor plate or a spacer, it is part of the carb, as it has sveral vacuum ports as well as the throttle mounted to it.

Now for the TFI upgrade (I'm searching now, but just real quick), what is its track record compared to a DUI?

As for the Howell TBI, you mentioned Tim that it didn't have spark control. What is that and why do I want it?
That's all for now...I know, poor excuse for a Jeeper. Honestly, this is the first day I've gotten home with some daylight outside, and the kids are first dibs on my time. I will keep you updated!

 

the Napa catalog says that the 4TA4 fits a 1974 360 4V Wagoneer, and is a 4300 Motorcraft carb. Here's a picture of a 4300 from the web:



If you turn the carburetor over, it ahould have a square pattern, ie all 4 venturis the same diameter and arranged on the corners of a square. If square, this is good - it means that you can use several aftermarket carbs on your manifold, or that you can get an adapter to mount a GM throttle body.

TFI stands for "thick film integrated" IIRC, and refers to the EI-core high voltage coil that is used with this upgrade.

AFAIK the DUI is the GM HEI ignition with some aftermarket parts. You can get the same results with a factory HEI fitted with, say, a MSD coil and a MSD module. IMO you may as well use the factory GM HEI parts on a Jeep, since you probably won't see any benefit below 5000 rpm or so.

The DUI may have a different advance curve than the GM HEI (high energy ignition), but you can get the same result using the Accel adjustable vacuum advance and weights kit http://www.jegs.com/webapp/wcs/stores/servlet/category_10001_10002_11563_-1_10381 - also, I'm not sure it really helps you much with a Jeep at our typical engine speeds.

The TFI upgrade is basically equivalent to what you get with a factory GM HEI. Using the Duraspark distributor and module, a higher voltage coil is fitted, along with a new rotor, cap and wires that accomodate the higher voltages without arc-over. You need to regap your plugs wider too, just like with HEI or DUI. The new parts are what the factory uses for some Ford applications that use the same distributor.

I don't know that there have been any heads-up comparisons between your options (DUI, TFI, HEI) but on paper they are all basically equivalent. From what I've read, it seems like everybody that has done one of these (easy!) ignition upgrades has been very happy, and noticed an immediate improvement in starting and idle, in particular.

Ok, spark control. As delivered, the GM TBI is more than just an electronic carburetor. In addition to fuel-air mixture, the TBI computer can also control spark advance at the distributor, aka "spark control." Controlling the engine timing is another way that the TBI can optimize the performance of the engine. I think spark control is also important on these engines to control pre-ignition and/or detonation, as well as boosting economy and performance.

The Howell kit is basically an electronic carburetor, and only controls the fuel-air mixture. The capability for spark control is there in the computer, but they just don't use it. For spark control, you need a distributor that can receive a signal to control spark. The GM HEI can accept a module with that input, but the same module can be used with the TFI (external mount) or presumably the DUI (recall that the DUI is a hopped-up GM HEI).

hth!

 

fyi I have a cj5 304 2bl 3.73 gears 33 tires. And I get 20 mpg high if I keep it about 55 mph. I have had it up past 80, but found out real quick I NEEDED A SWAY BAR

Our drivelines are about the same. For me 304 is a great motor. If you go with a larger bang bang, there will be some blow right past you on the trail with a stock four banger. Unless you are a mudder you will not need the larger motor. Also reminber you have to feed the beast and basicly 3.60 gallion. Just mine two cents. You are losing a lot of fuel somewhere. Also check your compression.

I covered to HEI about two years ago. I just went to the parts store and order Mallory HEI. It has a GM cap, rotor, coil. I love it no adjusting points. About a mouth ago coil went out. Not a problem GM coils are instock everywhere.

As for the carb. I would keep the beer and pizza coming for your friend till it is adjusted right. Thats what I do.

 

:iagree: A compression test would be very helpful

 

Here is a good link to a junkyard swap to install a high performance ignition. Dude goes by the name "Junk Yard Genius"

http://www.jeepsunlimited.com/forums/showthread.php?t=871709

I also have a word document that has three levels of ingition upgrades. Good info. I'll email it if you want.

 

My buddy had the same problem, stalling out when accelerating and backfiring thru the carb/exhaust. We thought it was carb related also. Found a bad ground wire in the distributor. Fixed it and bingo, back on the road again.

 

Update

Update:

My buddy came over tonight to take a look at the carb. Here are the findings:

1) Accelerator Pump - Somehow got disconnected, reconnected it and the bog while cracking open the throttle went away.

2) Fuel Pump - Leaking pretty badly. (I should have mentioned that previously because I knew that all along) I have a spare.

3) Plug wires are in rough shape, and not insulating well.

4) COMPRESSION - Here's the biggie. First cylinder on pass side had 0 compression, and the rest of the pass side cylinders were between 60 psi and 70 psi. The driver side cylinders were between 90 psi and 105 psi.

Path forward: Replace the fuel pump and plug wires, drive it like that for a while until I can save my pennies and get a 360. My buddy said to me, "yeah, you could fix it, but we need to look closer to see why no compression on that one cylinder. It could easily end up being close to the same amount of work, so why do the work twice since you eventually want a 360 anyways."

Future Plans:
1) Replace engine with 360 long block
2) Leave 360 mostly stock, with the exception of a mild cam upgrade.
3) Fuel Injection (probably one of the TBI setups)
4) DUI or TFI upgrade to distributor

I figure this should get me a strong reliable engine, that should return (hopefully)12-14 MPG, and a good 350 or so lb.ft. of torque, which should handle all the bumps and wiggles found off-road, and should be able to handle an elevation change from 4000 ft to 12000 ft in the same day.

Comments?

Thanks for all your help!

 

I'd say you have a stuck or burned exhaust valve in one cylinder. Napa sells an adapter that chucks up to your air compressor hose and screws into spark plug hole. Hook that up (NOT with engine running) and see where the air goes. It only has three choices:

1. intake (stuck or broken intake valve)
2. exhaust (stuck, broken, or burned exhaust valve)
3. crankcase (burned piston, or broken valve punched a hole)

Even worn rings will generate SOME compression.