Gutless 401 ?

[Stuka]

If the timing chain is really worn, that could certainly make it sluggish. Reared can timing will really hurt mid to top end power.

Although I am not sure if it could get five degrees off by just slack in the chain. But interested to see what you find out.

[Triumph215]

Drove the truck today, it runs much better, still not great but we're moving in the right direction. I've been fighting a choke problem, the spring came away from the housing last week and I put it back in backwards. LOL That took me a week to figure out. The Idle is great, stumble is gone, still need to start working the idle screws in. Still need to check timing chain slop, I hope it's ok, I really don't want to take that cover off...

[Triumph215]

Still chasing my no power problem, I still have a misfire or something under load. Vacuum gauge at cruise has come up a pound to 11-12lbs and power is improved but the needle wobbles 3-5lbs under a decent load. Pulled all plugs and regapped them at 0.040, they are Autolite 65's, plugs 4, 6 & 7 are all black and wet while everything else is nice and tan. After much searching I cannot find an explanation of which side of the carb feeds which cylinders but Chevy firing order is the same so I'm going to assume this works for AMC too. Using that assumption the deep plenum should feed cylinders 1, 4, 6 & 7 which is three of my 4 problem spark plugs. I'm going to change plugs out but am guessing that's not going to solve my problem although regapping them did improve the needle wobble about 50%.
I just was in the carb and everything looked very clean. Where might I have a flow problem just on one side and seemingly in the secondary system?

[Stuka]

When just cruising, typically the secondaries are not open. Although if down on power, you might just have to go into the throttle enough to do so.

The primaries have an idle and a cruise circuit. The secondaries only have one circuit as I recall (been ages since I had a 4350). What you are seeing suggest one side of the carb is perhaps too rich in cruise mode. Cruise mode is adjusted by the rods, and there are two ways to adjust them. The part that holds the top of the rods can be threaded up and down to adjust the fuel flow for both rods together. Or, each rod has a screw on top that adjusts each rod individually. I am betting one of these is not set to the same level as the other.

The fluctuating vacuum you describe is most likely the miss fire.

[Triumph215]

Interesting thought about the metering rods, back to that in a sec.
Being that the only thing I haven't changed in the entire ignition system is the plugs I'm going to start fresh there. Especially since I just put the carb back together and took great care to balance those metering rods on the hanger. I have the new Autolite 65 plugs in and gapped at 0.044, I probably could have gone wider but let's see where this gets me. If I still have the misfire and get bad plug color in the same cylinders I'll start thinking about those metering rods but it's contrary to all my instincts about carb balancing, adjusting those rods so they aren't the same makes me think I'm masking the actual problem.

[Stuka]

Interesting thought about the metering rods, back to that in a sec.
Being that the only thing I haven't changed in the entire ignition system is the plugs I'm going to start fresh there. Especially since I just put the carb back together and took great care to balance those metering rods on the hanger. I have the new Autolite 65 plugs in and gapped at 0.044, I probably could have gone wider but let's see where this gets me. If I still have the misfire and get bad plug color in the same cylinders I'll start thinking about those metering rods but it's contrary to all my instincts about carb balancing, adjusting those rods so they aren't the same makes me think I'm masking the actual problem.

True, its typically not required for such a mild engine. Some less conventional intake manifolds require it.

Will be curious if the plugs just end up looking wet, or if they go black pretty quick, which could mean oil. Hopefully that is not the case.

[Triumph215]

So I changed the plugs and it ran worse, go figure. So I reset the idle speed and started working the idle screws in and FINALLY have a steady (for the most part) vacuum signal. The needle wobble is mostly gone in all rpm ranges and my idle vacuum is up a pound or two to 18lbs, the hesitation off idle almost gone. Cruise vacuum increased to 12lbs or so, vacuum is improved everywhere and the truck runs very well everywhere except there's still no power on the highway. I found Ristow's post about distributor tuning and backed my vacuum pot out to come in a little later but it didn't improve anything. I'm about out of ideas.
I see in Ristow's distributor post that I can flip the mechanical advance weights and reduce mechanical advance by 10 degrees. I'm going to look in the TSM and see if I can find out what the mechanical advance is supposed to be in stock form.
I do regret not changing the main jets when I swapped the metering rods and I plan to take the top off the carb and change those jets out. I also guessed at the metering rod vacuum hanger thing height and it's probably the source of my marginal off idle hesitation so I'll richen that up half a turn or so while I'm in there. Am not expecting any big power gains at this point but will keep trying until it's clear there's no more to get.

[letank]

still using the autolite? and gaped at .040... may be the stock champion RN12YC (#404) gaped at .035

Time for a spin test drive with a chrono and see how long it takes to got from 0 to 60mph... or 0 to 400 yard

If you do not want to deal with the weights, connect the distro to intake manifold, your idle may be too high, but it is a quick test.

[Stuka]

I don't think you want to reduce your mechanical advance. Changing out the springs to change when it kicks in is certainly a thing, but pretty rare to reduce the actual advance.

I know its a lot more work, but I would only make one change in the carb at a time. If you change more than one thing at a time, its hard to know which change had an impact and what that impact was.

Good it improved from where it was. I previously did not mention changing the idle mixture screws as I figured that had already been tried. But glad it helped.

[Triumph215]

Yes Duraspark with Chevy module, runs great in town, lots of pep. Rev it in the driveway, and it sounds great, good vacuum, clean run up, totally smooth. It's just uphill on the highway. I've been mulling this and it's a load problem above 2,000rpm and it's been this way since I brought it home, everywhere else seems very good now. I'm starting to wonder if I have a pinched fuel line. I might crank some gasoline into a bucket tomorrow to see what kind of fuel flow I'm getting.

[Stuka]

Yes Duraspark with Chevy module, runs great in town, lots of pep. Rev it in the driveway, and it sounds great, good vacuum, clean run up, totally smooth. It's just uphill on the highway. I've been mulling this and it's a load problem above 2,000rpm and it's been this way since I brought it home, everywhere else seems very good now. I'm starting to wonder if I have a pinched fuel line. I might crank some gasoline into a bucket tomorrow to see what kind of fuel flow I'm getting.

I assume the fuel filter has been replaced. But what you describe could be a fuel starvation issue. There is also the sock in the tank, although on our jeeps its pretty course (more of a brass screen), its not like one you find on a newer vehicle.

[Triumph215]

Ok, I'm done for awhile. The fuel lines are clear, the filter is clear, no fuel or return lines are kinked, the float is set at the proper height, i richened up the metering rod hanger and my flat spot off idle went away. I have learned that a carburetor is a very sensitive thing and little changes really show up on a vacuum gauge which I've been driving around with for the past few weeks. I couldn't get the main jets out of the reman and didn't force it but they are visually so close to the stock ones that I'm calling it good. Idle vacuum is up to 20lbs and cruise is up to 12/13lbs. The vacuum needle wobbles like hell just before the transmission shifts but everywhere else the needle's pretty steady now. I'm going to buy a better quality distributor cap but at least I'm not losing speed on the hills now. Overall I think the motor's doing the best it can to pull a heavy truck. Still though, I thought it would have more balls.
Oh well, it's good enough to leave alone for awhile while I turn my attention to paint.
Thanks so much to everyone who chimed in to help me get it tuned properly. This is a great group and I appreciate the willingness to help a fellow Jeeper.

[Stuka]

Good to hear it’s at least running well now. And yeah, Tony carb adjustments can make a huge difference!

[dbx11]

The duraspark module is what you are running ? That does work fine but limits the spark potential, I ran one for a while in my truck with a fresh rebuild then went to the summit cdi box and it improved starting and all around drivability. Cheaper than the msd6 but installs the same way. I ran a used msd6 box on the wagoneer after banging my head like you did on issues that I thought were carb problems but weren’t. It is a worthwhile ignition upgrade and I’ll do it on all future projects that I take on.

[Mtnmax]

This is kind of an after thought...

Are you sure you have a 401? Some sellers will advertise a vehicle having a 401 when it's really a 360 or even a 304. They all look the same to the untrained eye and bolt pattern is the same.

[Triumph215]

Post script - The truck is running as well as it can and I’m on a road trip. Well today I filled twice with ethanol free gasoline and it made a HUGE difference. The truck can hold speed on hills and even slowly accelerate unless it’s pretty steep, gas mileage improvement too.
Yes it’s a 401, it’s cast on the block, tag on the valve cover and on the build sheet.
I still suspect my cam is worn. Will check it one of these days.

[Stuka]

Glad it’s running well enough for a road trip!

[Triumph215]

Me too and thank you.
1,100 miles over 4 days with that pesky diff plug being my only issue.
There’s no way I could have gotten the truck sorted so well without the gracious help of this amazing community. Thank to all so much.