1968 J3000 -Ignition and Fuel Tune Up

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Harry Dawg
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1968 J3000 -Ignition and Fuel Tune Up

Post by Harry Dawg »

*VIDEO FOR CONTEXT*
https://youtube.com/shorts/_tfHteLj38M?feature=share

Morning Y'all.

Hope everyone's weekend is off to a good start.
Mine is going good, but it would be better if I could get this truck to idle!

I think it's not getting enough fuel. I adjusted the floats to the recommended TSM setting for the 4BBL application (bottom of sight glass), but my fast idle does not seem to be on par with the 1600-1800 RPM recommended. Curb idle screw is set to expose a rough square in the transfer slot, and idle mixture screws are roughly 1-3/4 turns out. Fast idle screw is at factory settings.

I don't think I have any vacuum leaks, as I did the spray down test with starter fluid and there were no changes in RPM.

Do I need to adjust timing to account for the larger carb? When pressing the accelerator there is no throttle response, which leads me to believe either under-fueling or an issue with the ignition.

You can also hear it back firing a couple in times in the video, but this could be a fuel/air issue.
You can also hear it erratically pickup for a second and the idle events out.

This was originally a 2 BBL truck for context, but the TSM shows that there was an option for a 4BBL intake with a Holley 4160.

Carb is a Quick Fuel Technologies 425 CFM.




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Last edited by Harry Dawg on Sat Dec 10, 2022 9:34 am, edited 1 time in total.
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tgreese
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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

So a Quick-Fuel is a Holley 4150? If you are starting with a _new_ Quick-Fuel carb, there should be a book about how to tune them. What kind of choke is fitted? I'd guess the choke setup is completely different between the QuickFuel and an OEM 4160.

OEM carbs tend to be "small" compared to aftermarket, since the OEM app values economy and emissions more than a hot rod app. Small CFM means more vacuum and better fuel control, generally.

What I would do - read my Holley book and tune it according to the aftermarket book, not the TSM.
https://www.amazon.com/s?k=Holley+4150+carburetor+book
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Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

I am sure there are minor differences. The QFT I purchased doesn't have an adjustable secondary metering block. I think the 4150 would also have a slightly higher CFM rating.

The QFT is very similar to a Holley would be a better way to phrase it.

Currently have an electric choke, which I adjusted this morning for lower temps.

After hooking up a vacuum gauge to full manifold vacuum, my theory on timing seems to be looking more and more like the culprit.

See video below, which indicates late timing.

I have never messed with timing before, so I am a little anxious to get my feet wet.

Do I just rotate the distributor clockwise to advance timing a couple degrees? Before hand, I am guessing I will need to get #1 Cylinder at TDC?

https://youtube.com/shorts/xu359KYuTZQ?feature=share



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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

Depends on whether you want to measure the actual advance or not. If you want to adjust by vacuum, loosen the clamp bolt and rotate the distributor. Tweak to peak vacuum.

If you use a timing light (what I'd do), the inductive pickup of the timing light goes on the #1 spark plug wire. There are marks on the fornt pulley or balancer and some kind of pointer. Good idea to highlight the pointer (rotating part) with white paint or White-Out so you can see it. The timing light will fire with the #1 plug and flash. This strobe will show how the degrees pointer aligns with whatever rotating pointer your engine has at #1 TDC.

Recall this is _baseline_ timing; no vacuum advance (vacuum advance can disconnected and the hose plugged) and idle speed (no mechanical advance).
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Thanks Tgreese.

I am wanting to set the initial timing.

From my understanding the vacuum advance comes into play at higher RPM's.

TSM recommends the method you mentioned as well. I am going to hunt down a timing light, and will report back when I find one.

I am hoping the valve train didn't take any damage from the incorrect timing.

Is this the type of condition that causes the valve to contact the piston head?


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Re: Rough/ Erratic Idle on Cold Start

Post by letank »

Our engines are non interfering so your valves will not have close encounter with the pistons

Counterclockwise to advance.

your video is set on private viewing, so no access is granted.

If you can get a timing light with advance set up and rpm reading, they are very useful.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Thanks for the info letank.

You curbed a bit of anxiety for me lol.

I did get a timing light. It has degree marks on the back for some sort of adjustment.

Sorry about the video links. They should work now.

Going to try the light and will see what is to be seen.


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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Alright.
I hooked a timing light up to it, and I think I have an issue with the actual ignition rather than timing.

As you can see, the light doesn't seem to be triggering in a predictable manner. To me this indicates that a spark isn't being passed to the plug on every combustion stroke.


I do have a theory on why that is.

The truck has an electric spark box, which I understand produces 5,000 to 10,000 volts versus the factory 12V system. I accidentally left the key in the "ON" position one day, and I saw on YouTube that this can fry the distributor cap.

This would explain why I am getting inconsistent spark and random misfires.


https://youtube.com/shorts/vC_Vd-IYt10?feature=share


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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

Not sure about that post's reasoning. Can't see how arcing can happen if the engine is not turning.

Looks like a misfire to me. You can assess the distributor cap and rotor by inspection.

If this is a "new" build, I'd suggest all new ignition parts, including spark plug wires.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Well, I guess I figured that the hotwire that goes from the coil to the middle of the distributor could have messed up that main contact point.

I'm kinda learning the ignition system as I go, and am still not well versed on the details of how this ignition setup works.

The PO (my great grandpa) installed a Summit Street and Strip Multi-Capacitive Discharge Ignition System.
The way I understood it, the spark box sends power to the distributor cap and then it is distributed by something inside to the individual wires.

Fixing to pop the cap off and see what it's looking like.

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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

Maybe. You should simplify and measure.

The Summit box should send a high-voltage pulse whenever it is triggered. You could remove it, to make your diagnosis task easier, then add it later.

The ignition coil makes a high voltage pulse in response to the points opening. That will work without the capacitor discharge (CD) unit. The CD unit is an enhancement to the inductive discharge (the coil).

I would first inspect all the ignition components. The wires are often neglected.
Last edited by tgreese on Sat Dec 10, 2022 4:32 pm, edited 1 time in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

So it looks to me like the middle point of the distributor cap is not functioning as it should.

I thought that little stud was supposed to move up and down, but it doesn't move.

Distributor looks okay based on visual inspection.


https://youtube.com/shorts/Acv7Ira7YtY? ... d169bc.jpg[/IMG]

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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

Depending on the design, the rotor should touch the central button. Either the button must move, or the flexible contact reach up to contact it.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

The wires looked good.

They were even hi-temp, which I imagine would be better for the aftermarket ignition.

Plugs were replaced a few months ago.

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Re: Rough/ Erratic Idle on Cold Start

Post by tgreese »

How old are the wires? Hard to eval by appearance.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Not sure about that. At least 5 years old, as that's how long I've had the truck.

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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

While I'm here, I want to inspect the points.

How do I get the mechanical advance cams out in order to access points and condenser? ImageImage

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Re: Rough/ Erratic Idle on Cold Start

Post by sierrablue »

You shouldn't have to pull the mechanical advance to get the points/condenser out. A long skinny screwdriver and maybe turning the engine to a spot where the weights are out of the way outta be enough.

The points look pretty new, but since you've had it 5 years and never messed with it, I'd be willing to bet that the dwell is out of whack, and that all you gotta do is adjust the points and you'll be good again (for awhile).

Also, I see you're in GA, how cold is cold? If you adjusted the choke to be way too rich for the temp that could make the engine get loaded up and thus run poorly/not idle high enough.
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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Thanks Sierra blue.

Gonna get my lazy tail out of bed and go down there and mess around with it.

I saw an excerpt from the TSM covering dwell, but I need to look into this a little more. I figured the points may have gotten some crud on them, but might as well do it right.

I don't have a dwell meter, so hopefully there is a way to set it without.

It's 49 today in GA. Yesterday was 55.
We get pretty rapid temperature fluctuations, but average temps are in the 50s this time of year.

I set the choke to stay closed a little longer because it would stall out once the choke came off.

It actually will run continuously the way it is set now, but again it seems to be missing.

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Re: Rough/ Erratic Idle on Cold Start

Post by Harry Dawg »

Got the points and condenser out. Everything appears to be relatively new. Points look to be in good shape.

There is a little grease built up on the contact block, but other than that everything seems to be okay.
ImageImageImage

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