1968 J3000 -Ignition and Fuel Tune Up

[Harry Dawg]

So I think I am going to stay away from the PerTronix unit for the time being.
Really I would just like the truck to run, and IME adding variables increases difficulty of a root cause analysis.
I don't have the electronics knowledge to confidently install a system like this at this time, and I like the simple, mechanical reliability of the points.

The ONLY reason I think this may be an ignition problem is the misfire displayed by the timing light.

The ignition system is the exact same as when I got the truck, except I swapped the spark plugs out. Never touched the MSD box, wires, distributor etc.

I don't think I have a vacuum leak, as I have done started fluid test all over the top end of the motor and have gotten no change in RPM.
I installed the intake and carb TWICE just to be sure, and ran a leak down test on the top end using an air compressor and smoke pot.

Back story on the truck just for reference.

We drove the truck home with the factory 2BBL carb & intake and mechanical pump. Ran fine for a couple months.
Shortly after getting it, the truck would run, but only at high RPM. (wouldn't idle)
I assumed this was because the carb was junked up ( gas tank was rotted through, and there was rust in the inline filter)
At this point I started in on the body work and have just now circled back around to the mechanics.

Fast forward to 3 or so months ago.... Truck still isn't running.
At this point I swapped in the 4BBL carb, and a 4BBL intake manifold from and AMC Marlin.
I also installed a pull through electric fuel pump for priming, new gas tank from BJ's but am still running off the mechanical pump.

Fuel system is functioning fine. Fuel pressure is at 5 PSI.

Carb seems to be working as it should. It is maintaining fuel level in bowls, getting good atomization etc. The choke is not getting hung and fully opens after a few minutes of operation.
I don't think the addition of an extra 2 BBLs is the issue, as the CFM rating is in line with what I need for this motor.

I was thinking that I might have a possible disturbance to the air plenum in the manifold due to the exhaust cross over.
Maybe the intake fuel charge is being disrupted on it's way to the runners?

I don't have a tachometer. Since the truck barely runs, I am having a harder time tracking down potential issues as I can't get any steady readings from diagnostic equipment (timing light, vacuum gauge etc) are unreliable at this point.

[Harry Dawg]

Also, any external adjustment to the carb basically has no effect.

I haven't tried to kill the motor off, but I have tried to get a steady idle at 3+ carb settings to no avail.

I have tried it with floats set at half way up sight glass and at bottom of sight glass.
With curb idle screw turned in and out. (exposing less and more of transfer slot has no effect on idle quality)
Idle mixture screws have been set twice - one on a lean setting and one rich.

I can't get any reaction out of the carb tuning, so I think my issue lies elsewere.

[sierrablue]

Usually those screws don't make a huge difference--they do fine-tuning and such. If you adjust them enough they CAN make a big difference, but if you adjust them by quarter-half turns at a time (which is the right way to do it), it won't magically make the engine run a ton different. I always set the timing, followed by the RPMs, followed by tuning the mixture until I get maximum vacuum--then if the idle comes up I'll bring it back down and double check the timing.

If it ran fine with the 4-barrel manifold when you first put it on, and you know you didn't drop anything down it (and mice didn't pack it with anything), the manifold it fine. The only way the exhaust would be a problem (especially if you've verified that the manifold doesn't leak), would be if the intake were somehow cracked inside. I suppose the exhaust ports could be plugged, which would cause there to be excessive backpressure, but I think you would have noticed if that were the case, when you had the manifold off. On that note, I'd make sure the exhaust is flowing properly too, out the tailpipe and everything. If you have something plugging that up, the engine can't breathe and will run poorly--it's like if you were put in a vacuum with only just enough O2 to keep you alive and everything else is CO2.

At idle the CFM of the carb makes zero difference, frankly 2-verses 4-barrel shouldn't make any difference. Those plates are totally closed off at idle (as tgrease said, assuming you don't have it set too high).

To check the RPMs, if you're getting new points you'll need the dwell meter anyway, and usually they're tach and dwell meters--you flip the switch and it tells you how many RPMs it's at, then flip it back and it tells you the dwell angle again.

Pertronix is honestly easier to understand than the points are as far as installation goes. You have a red wire that goes to the positive lead on the coil and a black wire that goes to the negative lead on the coil and you're done. No condenser or anything and if you took out the box, it would be just the 12V (probably with a resistor if I had to guess) wire going to the coil. There isn't anything else to it--it bolts in in place of the points after you put the magnetic ring on the weights and you're done.

When you replace the plugs I'd recommend that you do a compression test on the cylinders--make sure they're all firing and making power. Also not sure how old the engine is--is it possible that the timing chain is worn out and either a) causing too much movement for things to run smoothly or b) is it possible that it jumped time, and now everything's all out of whack?

[Harry Dawg]

Changed the spark plugs, no effect.

I tested all of the wires for continuity and all were measuring 13Kohm to 17Kohm.

I don't know what the wire is made of so I can't confirm if this is within spec, but seems reasonable.

I also put the factory intake and carburator back on to confirm 2 things.
1) That the 4BBL intake isn't warped (The 2BBL is an exact fit)
2) That my QFT carburator isn't a dud.

I know the 2BBL is getting fuel.

Haven't replaced the cap and rotor yet, but did clean everything when I put it back together.

I have a pending deal on FB marketplace for a dwell meter, so if I can get my hands on that it will eliminate the points as a culprit.

On a side note, since this is the 3rd time I've had to monkey around with my intake/carb configuration I decided to time my removal and install. I did it in an hour and a half, which I thought was pretty good.

It would have gone faster if I hadn't dropped one of the intake bolts under the beer fridge, which resulted in about a 15 minute slow down.



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[Harry Dawg]

Reinstall time of the 4 BBL setup broke the previous record at 1 hour and 11 minutes.
Took a gander at the valves while I was in there.
They look pretty crusty. Hoping when she gets running some of this will burn off.
Probably need to do a valve job on the old girl at some point in the future




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[Harry Dawg]

Update-

Replaced all ignition components and it runs better, but still is just barely idling.

I also purchased a NOS SunPro dwell meter, but unfortunately it did not give any read out when attached to the negative coil terminal and engine ground.

User manual said for vehicles with high discharge ignition to hook to engine tachometer instead, but this truck does not have one.

Thinking of getting an electric dwell meter and seeing if I can improve idle quality with this.

Also, you will see at the end of the video I try and give it gas and it has no throttle response. Would this be indicative of any problem in particular?

https://youtu.be/IW00FPLhTxY



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[sierrablue]

I dunno on all the issues you're having, but the negative coil post IS where the tach wire goes, so that shouldn't change much.

In my experience no throttle response is either an issue with how the carb is jetted/tuned (or a sticky needle), or not getting enough advance out of the distributor.

Setting the dwell will certainly help with your response, engine noise, and general running quality.

[Harry Dawg]

Okay. Thanks for the clarification.

It sounds like the meter may just be expired then.
I have an electric one coming today, but prefer the analog version.

Hopefully the dwell is the issue.

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[sierrablue]

I mean I guess it's possible that it's set at 0 dwell and that's why it didn't move...but if you set it to tach and it didn't move it's probably dead.

[tgreese]

You can set the dwell by eye - make sure the points are open on the peak of the cam and closed on the foot, and kinda split the difference. Won't be optimum but it'll work ok.

Agree if you can't make the dwell meter move and the points open and close, the meter is likely kaput. Should also show you an RPM reading.

[Harry Dawg]

Okay. So I have tried 2 different dwell meters, and neither of them indicate any sign of life.

Of course it's 24 degrees this morning, so I can't get it to fire up but the results are the same even with it running.

I can't tell about the points by eye just because of the mechanical advance weights.
I can only get the slightest glimpse of the assembly, and the contact points are all but hidden.

This is starting to feel like that movie "Groundhog Day".

The only thing I can think is that the points are stuck open or closed, therefore the current never breaks and gives a readout on the meter.

Is it even possible for an engine to halfway run under these circumstances?

https://youtube.com/shorts/kmt_Cb6SOUc?feature=share

https://youtube.com/shorts/4NK5k3cc140?feature=share

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[tgreese]

Sounds to me like you have the points so far out of adjustment that they are always open or always closed.

Electrically, points are really really simple. Just a switch, on or off.

Do you have a test light? A bulb with two pieces of wire and alligator clips will work, or a bona fide test light. Cheap if you don't have one.
https://www.amazon.com/TuNan-6V-12V-24V ... ive&sr=1-3

Key on, test light from the positive coil connection to ground. Light on, points are open. Light off, points are closed. Light should flash as you crank the engine. The dwell meter measures that flashing, either on/off fraction for dwell or rate of flashing for RPM.

[tgreese]

Oh. Looked at your videos.

Who told you the dwell meter would work with the CD box? May not... The points only turn the CD box on and off, and are relieved of the big inductive kick from the coil primary. The meter may not detect the very mild switching of the points.

Try taking the CD box out of the circuit and running a conventional points ignition. Just reverse the connection instructions for points ignition (a Kettering trigger).

Suggest you do the test light first.

[Harry Dawg]

Thanks for the input fellas.

I couldn't find any supporting information as to confirm or deny it would work with CD box, so I was just operating under the assumption that it would.

I guess the saying holds true in this case lol.

At any rate, I have removed the CD box, and am in the process of rewiring ignition coil.

Ignition circuit highlighted in green for reference.

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[sierrablue]

Of course, if you unhook the CD box, I'd be tempted to leave it off...just one less thing to go wrong/cause problems, but that's just me.

[tgreese]

Possible you know this -

The green connection is only active while the engine is cranking. The starter solenoid bypasses the ballast resistor for hotter spark when starting. When running, the other connection to the ballast resistor connects to the ignition switch. This limits current to the coil during normal operation.

Kettering - https://en.wikipedia.org/wiki/Charles_F._Kettering

[Harry Dawg]

After removing the box and inspecting the wiring harness, it appears that some of the wires were frayed and grounding out on the wheel well.

@tgreese was right all along! I should have started here 2 weeks ago. I was afraid of unhooking the box and being worse off than I was, but it was easy to remove.

Rewired ignition coil, and then I removed the distributor cap and tested with the dwell meter, which indicated I was around 30°

After putting everything back together, it fired right up and ran for a couple of minutes!
We had a small victory!

Video for y'all to watch.

https://youtube.com/shorts/wc77GkWFki8?feature=share

Unfortunately once the choke came off it died.
I figured this was due to:

A) Curb idle set too low
B) Float to low

So today after work I raised the float, and it would not idle on choke. I then raised the curb idle a little to keep up which made idle even worse.

Since it was only half running, the bowl started flooding because engine couldn't keep up.

This led me to install a fuel pressure regulator I had lying around.

As luck would have it, it leaked like crazy, so I taped fittings up with Teflon tape. Also pinstriped a spider web on it just for fun.

Unfortunately being in a small garage, I began to feel sick from huffing gas vapors for 45 minutes while all this was going down so I called it a night.

Tomorrow I will lower float and hopefully get it to idle.


On a side note, I've been reading up on carb theory. Would recommend this book for anyone needing some good baseline knowledge.

Hopefully y'all can follow along with this mix matched, poorly written update. I'm blaming the gas vapors.

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[tgreese]

...
After putting everything back together, it fired right up and ran for a couple of minutes!
We had a small victory!

...

Woohoo!

[Harry Dawg]

Morning Y'all.

Been a while since I have worked on the J-truck. I got a request from a cute girl to take her for a spin, so I have to buckle down and get this thing running.

It started up that one time after I removed the spark box, and I haven't gotten her to run steady since.

If I pump the gas before starting, it will run decent for 5 seconds or so, then cut out.

This leads me to believe that it's not getting enough fuel. I have turned in the curb idle speed screw 1/2 to a full turn, but this doesn't have any effect. I pulled the carb and looked at it from the bottom, and the transition slots are right where they need to be.

I haven't messed with the fast idle cam because the vacuum secondary makes it difficult to access, but this might solve the issue. It is currently at factory setting.

I have also adjusted the idle mixture screws per Holley recommendations (bottom out, then back them out 1-1/2 turns)

Any ideas on what I could be missing here?


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[tgreese]

Measure the fuel pressure from the fuel pump. There is a spec in the TSM. You'll need a gauge, cheap at Amazon or Harbor Freight. Same gauge you would use to measure engine vacuum.

On an old car, I would expect to replace every rubber hose on the car. Especially fuel hoses.