Ignition help needed for my 1973 454 C/20

[RPOZ11]

Was getting a bad miss thru the rpm range.
Started going thru the system.
Checked the distributor, had the wrong one in it.
Apparently this one must have been rebuilt by someone in the past as the mainshaft/top cam piece did not touch the weights of the advance.
What I determined was is that the weights were floating , causing the timing to bounce around.
Replaced it with a correct housing.
Now have what I think is the correct unit having a 718 CCW distributor cam.
The weights contact properly now with the mainshaft/cam piece.
I cleaned up this replacement distributor, greasing up the weight pivot points,
re-tightening the vacuum advance, and adjusting a new uni-point.
The miss thru the rpm range is almost gone vs. what it was doing.

Items replaced :
R44T spark plugs
Accel 8mm wires
New Coil
MSD Cap
MSD Rotor
A new uni-point point/condensor

Vaccum advance was the used original from the replacing distributor.
I checked it and it pulls & holds 17-20 on a Vacuum Gauge moving the breaker plate assembly.
Vacuum at idle from the port on the QuadraJet is 0; 15-20 thru acceleration.

Now my current problem :
I set the timing at the balancer, vacuum advance disconnected & plugged, at 8* BTDC; per the Sticker from GM.
Got the dwell meter out, calibrated it to 0, got it to 30* on the points, then checked & re-adjusted timing at 8* BTDC.
What it is now doing is falling on its nose, power surging to almost no power under acceleration.
It wants to die instead of accelerate.

What am I missing?

Could a new replacement coil go bad?
When I first replaced this coil the rpm range came back.

Side note...
I have a thought that maybe the timing chain might have skipped a tooth...

Does anyone know of a distributor shop that can rebush and restore factory points distributors?

[f.monroe]

Is it a fresh engine? If so was the cam broken in properly? A friend had some of the same issues and that's what it ended up being.
Frank
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[RPOZ11]

No Sir, It is the original 454 GM installed in my truck back in June of 1973.
Stock bore... 115,000 miles

[f.monroe]

I assume it's a single points distributor?what gap are the plugs set at and is there an inline resistor to reduce the voltage at the coil?

Frank
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[RPOZ11]

Single point breaker plate.
I have tossed around using my dual points breaker plate but have decided to save those for my Camaro distributor.

.035 on the spark plug gap.

As far as i know, regarding an inline resistor, I am only using the Factory brown wire supplied from the wiring harness to the positive side of the coil.

[f.monroe]

It's been a while since I worked on points but I think there should be about 7.5-8.5 volts at the coil. If it is full voltage it will burn it up. I may be wrong but if you are going through coils I would look into it.
Frank
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[f.monroe]

Another thought is that the balancer ring may have slipped over the years. Try advancing the timing and running it . If it gets better advance it a little more. You may not be able to set it by the balancer. It might have to be set by the seat of the pants method.
Frank
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[RPOZ11]

Originally Posted by f.monroe

It's been a while since I worked on points but I think there should be about 7.5-8.5 volts at the coil. If it is full voltage it will burn it up. I may be wrong but if you are going through coils I would look into it.
Frank
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7.5-8.5 going into the coil ?

If so, then I am to be checking the Positive side wire?

If that is what you are suggesting, then should I disconnect the wire from the coil, switch on ( but not in the start position ), and measure the voltage thru the wire to the end of the terminal to be secured to the coil?

[RPOZ11]

Originally Posted by f.monroe

Another thought is that the balancer ring may have slipped over the years. Try advancing the timing and running it . If it gets better advance it a little more. You may not be able to set it by the balancer. It might have to be set by the seat of the pants method.
Frank
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I am aware of balancer outer rings spinning.
It's still the stock GM equipment installed.
I get 8* BTDC; and double checking it with the back dial on my timing light.

In the past, when assembling engines, I would paint a black stripe on the balancer.
If that line seperated, then I would know that the outer ring had moved.

[f.monroe]

Originally Posted by RPOZ11

I am aware of balancer outer rings spinning.
It's still the stock GM equipment installed.
I get 8* BTDC; and double checking it with the back dial on my timing light.

In the past, when assembling engines, I would paint a black stripe on the balancer.
If that line seperated, then I would know that the outer ring had moved.

If the ring has slipped then the timing light will show 8degrees and will show correctly when the advance light is turned back 8degrees.

I would try to advance it just for grins.
Yes it should be the lower voltage at the positive side of the coil. If you have 12 volts that may be correct also but I remember that some older coils require the voltage drop .
Frank
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[RPOZ11]

Here is what I get when I hook up the red lead to the positive side of the coil, black lead to ground, key switched to the on position 6.5 Volts in the Volts sweep indicator :

[f.monroe]

That's basically 7 volts. Probably correct. I am going from old memories. I do not have any old literature on servicing these trucks. Someone with a manual may chime in for exact specs. I know my old short bed 454 truck would run like crap every so often and it would retard the timing on its own over time. I knew when it was off because it would sputter and had a great loss of power especially under load. I would pull the distributor up a little and all was good.

How old are the plug wires? That's another thing that breaks down especially under a load or acceleration. i have seen them pur at idle and run like crap under acceleration and it was just bad wires.
Frank
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[f.monroe]

I like the analog meter. There are just so many Things you can do with with an analog that a digital won't do. Especially the newer auto ranging meters.
Frank
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[RPOZ11]

Originally Posted by f.monroe

That's basically 7 volts.

How old are the plug wires?
Frank
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New Items that I have replaced :
R44T spark plugs
Accel 8mm wires
New Coil
MSD Cap
MSD Rotor
A new uni-point point/condensor

Been thinking of doing a coil check but I have never done this stuff before.
In life, sometimes, necessity demands learning....
I'm just going for it here on the fly.
I've been fortunate enough to resolve the distributor problems up to now.
Process of elimination, comparisons of select GM parts I had laying around, along with obtaining 4 GM original 454 distributors for my year of truck actually helped me quite a bit.
The best results I have so for is that with all of the comparisons, checks, etc...
I was able to single out that the mainshaft/cam pole with the combination of weights installed were causing timing and spark variations.
NOTE :
It must be quite important to have installed the correct parts for your application;
this being a stock application...just to state!

[f.monroe]

Is the vacuum adv hooked up to the correct vac source? Ported or Venturi?
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[RPOZ11]

On my QuadraJet, I used the port above the baseplate.
Standing, facing the engine from the front of the vehicle, on the lower right hand side (driver's side) of the front of the carb, is the port that I used.
( I am aware that the QJ currently in use on my 454 is not the original issue QJ from GM. It could have issues internally; not sure yet.
I have 4 correct original QJ's that I intend to have redone; 2 restored and 2 for parts, to be installed in the near future )

The Vacuum advance that I used is the original from the replacing distributor.
I checked it and it pulls & holds 17-20" of vacuum on a Vacuum Gauge,also moving the breaker plate assembly.
Vacuum at idle from the port on the QuadraJet is 0" vacuum; 15-20" vacuum thru acceleration.

[f.monroe]

Sounds like the ignition may not be the prob. It sounds like it may be fuel. If you have any other carb you might try bolting it on for a test run.
I would have to look at a quadrajet to know which port is manifold vs Venturi.
Frank
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[RPOZ11]

Thanx Frank!
Words of suggestion and encouragement help make this a great website.

Actually,
My plan was a step by step diagnosis.
Since I have put off working on this truck over the years, I now HAVE to repair it as I am driving it daily; until I can get my SWB going.

Now that I have an ignition system that seems to be working off idle, and quite frankly, it seems to be running its best off of idle now, this makes me go to the next logical place : the Carb, just as you are suggesting.

I have 1 QJ rebuilt; but now that after comparing them, I am not complacent using it.
I think that I want to get one of my correct part # QJ's done and installed.

The fuel pump is also in question as well.
In the back of my mind, I have often wondered if the diaphram inside the fuel pump has become weakened.

The fuel filters are good, as well as the brass unit inside the carb.

I have previously removed the current QJ, cleaned it, retightened the securing bolts, and reinstalled it.
When I was going thru it at that time, I noticed that the securing bolts of the top & bottom plates were loose.
At that time I retightened them.
After reinstalling this QJ, it ran much better thru the RPM range.

[RPOZ11]

I tinkered around with my truck some more today.

I kept getting a fuel/air starvation after 40 MPH.

So, after looking ridiculous on the freeway today, with the engine surging and stalling at 40 MPH tops, I got off the freeway and nursed the truck to my local NAPA auto parts store.

Since owning the truck, I have no history of what the prior owner serviced, changed out, etc etc.

I decided maybe that I should swap out the fuel pump for a new one.

Kinda tight room to work with having a 454.

I got that swapped out, installed a new inline gas filter, then took her for a test drive.

I can hit 85 MPH now without too much of a struggle.

I still think I have the distributor in incorrectly.
I seems like it wants more timing and I have the distributor clocked to where the vacuum advance almost hits the valve on the back of the intake manifold.
I still have thoughts that maybe the timing chain is really loose.

Stock camshaft is a small unit; what I think it has is around 434" lift I/E. The duration I wish I knew.

Since replacing that distributor recently, and now with the new fuel pump, I can get more from it.

Also to note :
This truck has the thermatic vacuum switch on the air cleaner.
I think I had it installed incorrectly; receiving a constant vacuum pull, thus the valve door stayed shut.
This might have ALSO been adding to my surge/stall issues.
(Note: the QJ on my truck is not the correct OEM carb. I may be routing my hoses incorrectly based upon what ports I am using from a newer QJ)

Does anyone have a schematic of how to correctly route the vacuum hoses for the thermatic switch on the air cleaner?
( 1973 C/20 454 TH400 Quadrajet )

In the near future I will being swapping a stock GM cast iron low plane oval port EGR intake onto this engine.

I need to find out how to route that system as well...
Anyone???

[savatreatabvr]

Well RPOZ11, I have the same truck, (1973 C20 w/ 454) and I'm having many of the same issues your having! The thing that seems to have helped me the most over the months and months of troubleshooting is adjusting the valves. I've done the (running procedure) several times because these trucks are so old they tend to fall out of adjustment fairly quickly so it's almost a never ending battle keeping these beast running correctly! I also upgraded to an HEI distributor which has helped! Next I'm ditching the Quadrajet and going with an Edelbrock Performer carb, I've got a 1977 Dodge 440 Moho with a 850cfm EP carb and it purrs like a kitten so I'll try a 750cfm or 800cfm EP carb on the 454 and see if it helps my lack of power issue! Let me know if this info helped you!

[RPOZ11]

Hello.
Nice to hear from you.

On the Edelbrock QJ carbs that they make, I have not heard alot of positives regarding those.
I typically take my QJ carbs to a local rebuilder who does all of his tweaks, pluses, and special things to make them much better than the way they came from GM.
I have 3 original QJ's to take in for restoration and rebuilding.
2 will be done as original; the 3'rd as a core for parts; unless I have enough left over for a complete 3'rd carb.

I started with my carb, took it off, cleaned it, adjusted it, tightened all of the screws securing the top & bottom plates to the center body.
I also noticed that my QJ was missing the inline fuel filter inside the fuel line inlet of the carb.
So I installed that correct item.
That was a beginning of it runnning better.

I then went to the distributor.
My timing mark was bouncing around at the balancer/timing mark on the timing chain cover.
Discovered internal problems and decided to change out the replaced distributor that was in my truck currently, now having the correct GM part # ID on the housing.
With the points and condensor replaced, new wires, cap, rotor, plugs, the timing bounce it had went away nearly 90%.

My air/fuel starvation I determined must have been a combination of my incorrect vacuum line connections and the fuel pump.
The fuel pump was a resounding plus.
I believe that my air restrictions were due to improper vacuum line connections to the carb vent pulls.

I assume that my remaining timing isues reside in a loose timing chain, and most likely, worn valve guides and worn valve seats.
Re-adjusting the valves makes alot of sense.

I have decided to rebuild an extra set of heads, some 820's, that I have here while my truck is currently running on the 049 heads original to it.
Will buy a new cam; already bought some Delphi Anti-pump up lifters.
Will get a new Cloyes timing chain.
Gasket kit.

I cant wait to change everything over to newer rebuilt parts because I know it will run even better than I have it now.