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Distributor Cap not moving Timing on 78 CJ7 304 v8

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Hello,

Always gotten good help so hoping to get it again! 78 CJ7 with a 304. Has developed a backfire when shifting/letting off the gas. Have done new plugs, wires, distributor cap and coil, so trying to set the timing.

When rotating the distributor cap, the timing shows around 20 deg below TDC with a timing light no matter what position the cap is in. Have rotated far enough to kill the engine and the timing indicator doesn’t move. Any idea what could be causing this? Or what I am missing?

Thanks in advance!
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Time with the vacuum line disconnected and plugged (the hose) from the Distributor

Timing is done with the "correct value (degree)" along with the correct idle speed while doing so

------SEE SPECS (do you have specs---from where?)

When finished "Timing", you may have to tweak the idle speed as you do it a few times.

When you are done the Degrees and idle speed should be perfect----then reconnect the vacuum hose)

Then check idle speed again!

I always try to tweak my idle as I adjust the carb or the timing.

If you have an adjustable gun---what is it set on?

Is your spark plug wire pick up in an open area or close to other wires?

Is it on number 1 wire? Or do you have it on the coil wire?

This is the only 304 pic I have---not a good one---see the white mark?

Organism Gesture Font Wood Snout


Here's my Plain Jane non adjustable gun
Motor vehicle Tool Bumper Automotive exterior Automotive fuel system


Here's my Dwell/ Tach meter to check/set idle speed----It' s showing 500 RPM on the 6 cylinder scale (not correct for my timing degree---too low)
Audio equipment Motor vehicle Electrical wiring Gadget Computer hardware


This is ZERO (exactly)TOP DEAD CENTER----everytime my light flashes
Automotive tire Gas Wheel Automotive fuel system Tire


1980 specs for 258----Here's 8 degrees Before Top Dead Center (BTDC) @ 700 RPM EVERY FLASH---I magic markered my goal, it's hard to see the marks at the "guns angle"
---Now I reconnect my vacuum line and recheck/fix idle speed
Gas Motor vehicle Electric blue Auto part Art


Now that I have changed my carb to a Holley 390 4 barrel on my 258, I have my timing more like 16-20 BTDC (just sayin')

What is your Goal supposed to be? what RPM?

----JEEPFELLER
 

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Clarify something...
are you moving the distributor itself or just the cap? you say " distributor cap" in your post.
 

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BE ADVISED!!!

CAUTION!!!

THE STROBING LIGHT WILL MAKE YOUR FAN LOOK LIKE IT IS STANDING STILL!

FOR YOUR SAFETY KEEP YOUR ARMS AND LEGS INSIDE (rather OUTSIDE OF) THE RIDE!

------JEEPFELLER
 

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I thought that too---then I saw it was dying and figgered he meant the distributor as a whole???

----JEEPFELLER
When rotating the distributor cap, the timing shows around 20 deg below TDC with a timing light no matter what position the cap is in. Have rotated far enough to kill the engine and the timing indicator doesn’t move. Any idea what could be causing this? Or what I am missing?
Im sure wiser minds will correct me if Im wrong, but rotating just the cap would cause it to die as the spark " circuit " is broken by moving the rotor away from the contacts.
If he is rotating the assembly, and its not moving the timing, there would be no reason for it to die as nothing would have changed? That would be possible if the dist. gear wasnt engaging the cam gear or wasnt secure to the dist shaft, but then it wouldnt run at all as the rotor wouldnt be turning......
 

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The cap would have to not be fastened to turn it separately?

I was thinking maybe he was hooked to the coil high tension wire? Or against other wires? Hyper flashing!!!

-----JEEPFELLER
 

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Discussion Starter · #12 ·
Thanks y’all.
Try to answer the questions here. I think one of the main points I may be missing is pulling the vacuum line, did forget that part. Want to see anything else I might be missing though.

Using a plain timing gun, non Adjustable.

Spark Plug Wire pick up is clamped just above the spark plug on Cylinder #1

Stock target is 5 deg BTDC but may have to adjust since it was bought with an aftermarket Carb.

And go easy… I have been moving the cap. Realize now need to move the whole housing.Would explain why I’m not seeing a change! I guess it is likely the motor died from losing contact.

Would timing be a likely candidate for the backfire I’m getting?

Thanks for all the help.
 

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HI,
You can't move just the cap. it has a pin in it so it sits in one location .. if you move just the cap it is almost impossible to latch it back down. then it would NOT run and you are moving the wires.

good luck take care be safe
tim
 

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And go easy… I have been moving the cap. Realize now need to move the whole housing.Would explain why I’m not seeing a change! I guess it is likely the motor died from losing contact.
I will only laugh because I did the exact same thing the first time I ever tried to adjust the timing on a vehicle.. my buddies had a good time with me over it ;) :ROFLMAO: :ROFLMAO:
The sat there and watched me for almost an hour before saying anything..
 

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Discussion Starter · #16 ·
I will only laugh because I did the exact same thing the first time I ever tried to adjust the timing on a vehicle.. my buddies had a good time with me over it ;) :ROFLMAO: :ROFLMAO:
The sat there and watched me for almost an hour before saying anything..
Haha thankfully there was no audience I could see! Sure it would be funny to see myself get frustrated with it though! First one so definitely learning on it. Thanks for all the help. Hoping this will fix the backfire I’ve been getting.
 

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For a '78 304 I'm seeing 5 BTDC at 750 RPM

Idle speed is important---going faster makes the centrifugal advance weights to sling outwards, this changes your timing!

Keep it at 750---even if you have to move it back after changes.

Sorry to go "Romper Room" on you---It's hard to explain stuff if the basics have not been achieved 1st.

-----JEEPFELLER
 

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If the timing is set correct and the only problem is a backfire when letting off the gas, do you have the factory air pump (emissions) on the engine. If you do it has a diverter valve. If you do unplug the vacuum line, and plug the vacuum line. Run the engine and it should stop. Here's what the valve looks like NEW 79 86 Jeep CJ CJ5 CJ7 Cherokee Smog Antibackfire Gulp - Etsy. If not just discard.
 
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