Technical Rebuilt Motor Running Poorly, Need Advice

Well, I finally got done with my first engine rebuild... Or so I thought. So here I am once again. Sorry, may be kind of a long post, but I'm pretty defeated and at my wit's end.

Long story short, my 64 GP desperately needed a motor rebuild, so naturally I yanked the motor and built it myself. Got everything back together in a solid 2-3 months, fired it up, broke in the cam, and found out that the motor runs like hot garbage. It's low on power, idles pretty rough and low, pulls low vacuum, and overall just doesn't sound happy. I managed to limp it over to my mechanic, and he properly set the timing (I currently lack a timing light) and tried tuning on the carb a bit. Basically told me my carb (Carter AFB) had seen better days, and it was time for replacing. So I sourced another AFB in better condition, and it did run better with the fresh carb on it... Well, just a tiny bit-it still runs like hot garbage.

My 389's practically stock, minus an overbore of .060 total and an upgrade to the tried and true Pontiac 068 cam. I know for a fact I installed my rings right, correctly set TDC on #1, and basically did everything up to the carb correct.

So, here's what I observed. Before I swapped the carb out, I noticed my plugs indicated a lean condition, even after some idling, cam break-in and a bit of street driving regardless of any adjustments I did. Swapping over to the new carb mitigated the lean condition issue and, like I said, made the car run a tiny bit better. My plugs now indicate normal operation, with #6 being a little sootier than the others (dumped a bit too much gas into the intake doing adjustments on the new carb).

Moving on, next I pulled spark plug wires with the motor running. Motor just about wanted to die on every plug I pulled, but I noticed the least amount of action on cylinders #5, #6, and #8. I don't exactly know if it's usual, but I did notice a couple of the spark plug boots at the distributor were arching a bit when I tried adjusting the timing (ouch), but I'm not sure what cylinders they were.

I then decided it's time to pull the valve covers and watch my rockers with the motor running, while I have no tool to accurately each rocker, I did not notice a single thing wrong. Pushrods check and all rockers have oil.

And then I moved onto the distributor. I figured I'd try to touch the timing a tiny bit to see if any changes in timing made it run smooths, but to no avail. Then I noticed something interesting I didn't notice before-when I hooked up vacuum advance, there was zero change in RPM. It's strange though, as I've never had any issue with vacuum advance before the rebuild. Maybe sitting did a number on the diaphram which I'm sure was already ancient at this point? It really feels like it's running without vacuum advance.

Lastly sprayed carb cleaner around the manifold, carb, brake booster line, and vacuum line, and no raise in RPMs at all. I know the motor has good compression-I don't have a gauge to tell but I'm 99% confident on the compression. The motor doesn't stumble on the top end or when it's under load at all. It idles better under the new carb, granted I have to turn the mixture screws out a good 4-5 turns just to get it to idle. Throttle is still snappy, it just idles and runs poorly over all. I really think it's a vacuum leak, but I just dunno where to check.

I know it's impossible to fully diagnose an issue without being around the car, however any advice would be greatly appreciated. I just want it back up and running properly before winter sets in. I've included an imagine and two videos to give an idea of its condition.

(I also would like to note that in the video of the rockers, that droning nose is my disconnected brake booster)

Thanks for any help!

Image + Videos: https://imgur.com/a/VlULPci

 

Do you have the firing order correct.......the plug wires in the cap routed correctly to the plugs ?
Are your points adjusted correctly ?
Do you actually have a vacuum gauge reading ?
Are intake and exhaust valves adjusted correctly ?
Could there have been a mistake made in valve job with a valve not seating or valve or seat not ground correctly ?
Do you have an intake manifold leak where it joins the head on each side ?
Have you taken a compression reading ?

 

Another possibility, are you sure your timing marks are in the correct position, I believe they should be facing each other like a Chev, did you use a clockable crank timing chain gear, you may have the cam retarded.

 

No it's not normal to have your plug wires arcing. Maybe it's time to replace the wires, cap, and rotor as well. And also double (triple?) check the wires are in the correct firing order. I recently observed a wrong order situation that had many people baffled until it was checked by a fresh set of eyes.

 

What is engine vacuum?

 

Is a 389 like a 400 as far as valve adjustment just take them all the way down? I mean for hydraulics. Lippy

 

Two things You said was 1 vac advance did not make any difference connected and 2 noise from booster disconnected. Plug the vacuum feeds for both to see if that makes a difference. Sounds like vacuum leak a bad booster or vacuum advance could cause that.

 

Is the centrifugal advance working properly?

And a follow-up to the point about Pontiac firing order. If done wrong - CW like a SBC, it won't even fire much less run. Pontiac is CCW 18436572

 

Yes, a '64 389 should work like that with nominally stock cam like the 068

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Sorry for the delay, yes timing and firing order's set correctly. I had to go back through the distributor when I was originally trying to get it to fire, was a tooth off; double and triple checked plug wires are correct too. Rockers are non-adjustable and are torqued correctly and everything's lined up properly on the cam and sproket. I did forget to mention that I plugged my brake booster and had no change in idle. Stupid me didn't check my points though, so that would be a great place to start, haha.

I did put a vacuum gauge on it from the carb and, well, needle's a bit bouncy, as if there's a valve-related issue or weak compression in a cylinder, kinda making me nervous. Granted it smoothed out with just a tiny touch of throttle and only bounces quickly within a certain range. Based on my cabin gauge, it's pulling probably around 10-14 in/hg of vacuum. Don't have a gauge to test compression just yet, though I plan on getting one and testing it as soon as I can; I'm hoping there isn't a valve or compression issue.

I'm not entirely sure if my advance is working. It sure doesn't sound or act like it but I don't really have any way to check, and it really does sound like it's running without vacuum advance. Of course I'll go through and run other diagnostics, but thinking I'll pull the distributor and take a look at the advance and points. Maybe throw a set of plug wires and a fresh cap on it just to be safe.

I'm really thinking (hoping) it's a vacuum leak somewhere, considering I have to back those mixture screws out quite far just to get the thing to idle. The other thing I also forgot to mention is that once it's warmed up and I start it, my RPMs raise a tad after firing and drop down to idle. Dunno if that's... Usual, persay, but I've never noticed that happening before or on any old car. Not running a choke on it either.

 

Quick update. Checked my points and the gap checks out. Pulled the distributor and gave the VA cansiter a quick test. Doesn't feel like it's losing vacuum, but I'll replace it anyway to be safe. The only other thing I noticed was that my negative coil wire was loose, but I doubt that has anything to do with it.

 

do a compression test just because the rockers are not adjustable dont mean it dont need to be right

 

Oh yeah as soon as I get paid tomorrow, I’m getting my hands on a test gauge. Would rather be safe than sorry


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With a Chev with a hydraulic flat tappet cam, I adjust these while the engine is running, back off the rocker nut until the tappet starts to clatter, then tighten until the clatter goes away, then tighten the nut 1/2 to 3/4 of a turn allowing the engine to settle as this is done.
I do not have experience with Pontiacs do these adjust in the same manner as Chev. If they do then maybe the valves are staying open.

 

Don't want to send you off on a wild goose chase but I found when I changed the cam on my Olds 350 I had extreme clearance on the rocker arms- you could rock them back and forth. This was all with stock rockers/pushrods. When the rocker bolts were tightened down the lifters were supposed to be down in their bores by about .040". They were loose. I found out the cam I got had a smaller base circle than stock, so lifters were further down in bore than a stock cam. ( same lift, only starting from a different spot) I had to get adjustable pushrods. Don't know if your Pontiac is the same with non-adjustable valve train....

 

With the wiring arcing thing, watch it run in the dark to see how bad it is. A new set of wires may be in order to help it out.

 

Like other's said are You Sure the Firing Order is CORRECT,
I have seen a lot of cars guy's have done & its always the Firing order

Just my 3.5 cents

Live Learn & Die a Fool

 

Interesting, I’ll have to go double check my rockers-something that never really came to mind honestly with a non-adjustable valve train. Adjustable pushrods may be in line if need-be. I did actually notice some lifter clatter on the passenger side despite everything being sufficiently oiled.

In the meantime, I’m gonna start with a tune up on the distributor, re-checking order, and a compression test. Think I’m finally getting down to a solution, I appreciate the advice from everyone.


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Let us know what the compression is

 

Firing order Ok ?
Points Ok ?
Condenser ok ?
Base timing good ?
Ignition timing good?
Vacuum leaks?
Valve adjustment ?
Engine compression/ leak down ?
Carb set correctly?
Sounds like you checked most of these off. The bouncing needle on your vacuum Gauge has me concerned.
Broken or out of place valve spring would be an easy fix.
I’m suspecting internal engine issue related to valves.
Good luck

 

Pontiac had a change in PRlengyh in that era. Make sure yours are the right ones in replaced during the rebuild.
And we hope you used cam lube and break in additive with the new cam. Could have wipe out lobe or lobes if not.

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When you did the valve job did you check the valve stem height?

 

The low and bouncy vacuum sort of points to some valve related problem

With non-adjustable valve train it is important that the valve stem installed height be correct. And, if the heads are milled that can hold valves open. Can you provide some info on the machine work, especially the valves?

Not a lot of Pontiac experience, but have seen similar on Ford FE's. They have shorter pushrods available for that one. I think locking nuts are available for the Pontiac, to allow adjustments.

.

 

Two thoughts. Cam timing correct? If it's off the compression will be a bit low in all cylinders and engine will run like crap. Also you mentioned that you saw no change in the idle when you plugged in the dist vacuum. That is normal; the vacuum port in the carb is closed at idle.

 

Non adjustable valves in the 60's was a marketing term. What that meant was you didn't get the feeler gauge and socket wrench out every tune up.
If it has a rocker with a ball nut and a lock nut on top, the valves are adjustable. The 389 rockers are adjustable.

You should be running about 20" of vacuum on a stock engine. I believe your valves are too tight.

A 68 302 has non adjustable valves. I have a valve cover with the top cut out to adjust those non adjustable valves.

If your mechanic did not check valve lash, he's a dumdass for vintage engines especially one just put together.
I've had fresh engines that do as you describe here, they needed a hot lash adjustment.
If it was mine, I would do a running hot lash adjustment as mentioned. Oil is going to go everywhere so take precautions.

 

Ive had a couple old Pontiacs, 400's and 389's, all of them had the outer ring on the balancer slip. This led to setting the timing completely wrong and did exactly what you are talking about. I had to set the timing using a vacuum gauge. Buy a cheap vaccum gauge and hook it to manifold vacuum, disconnect and plug the vacuum advance hose, then crank the distributor around till it makes the most vacuum at idle.

Some thing to look at anyway.

 

^^^^^^^^
What this means is, if the damper marks are off, any lash adjustment on assembly will be off.
Solution....
Running Hot Lash Adjustment.
It's close enough to run, not well but run.
The poor performance, low vacuum, bouncy needle on the vacuum gauge and the Big Big Big One Rocker chatter on the passenger side is a big clue.
Adjust those valves.

 

The factory non-adjustable valve train bit me once on a Pontiac motor since I was more familiar to Chevrolet’s. I ended up swapping the rocker studs to BBC and used polylocks to adjust the valves since the Pontiac studs and nuts were setup to just bottom out at adjustment if I remember right.

 

As treb11 said...Pontiac is counter-clockwise on firing order..you sure you have it configured as such? I built my first Ford fe engine a few years ago and had it set up clockwise. It would start and even idle like shit til a Ford buddy showed me my error. Then it was fine.

 

Quick note: If money is a tad tight you can go to O'Reilly's or Autozone and "Borrow" a compression gauge meaning you pay the deposit on it and get the deposit back when you return it. Other parts houses may be doing the same thing. That saves having a tool that you only use maybe once every couple of years sitting on the shelf. Even with as many tools and equipment as I have accumulated in the past 60 years I do it.

Those Pontiac engines are usually pretty easy to have run smooth if everything is right. I worked as the front end mechanic in a Pontiac garage in Texas in the mid 70's and they never had much trouble getting them to run smooth.

That coil wire being loose or other wires jumping fire are all the ends on the wires. Still old spark plug wires are old spark wires and a cap will jump fire if there is dirt on the outside. Look inside the cap for any traces where spark was tracking across the inside.

Still the jumpy vacuum gauge probably is telling you more than anything else is. I don't think you will get 20 inches of vacuum as you seldom see that on any engine from that time period no matter how perfect the engine is. 16 to 18 and steady would be real nice though.

Just thinking, you did use those plastic pieces to hold the intake gaskets in place when you installed the intake? if the intake gasket slips a tad you could be experiencing leaks especially if the rough running is all on one bank.