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Discussion Starter #1 (Edited)
When I still suffered from no spark, the engine cranked like a champ. Now to tonight after adding a second engine ground strap, there's spark and the timing was adjusted to TDC per the factory manual.

Attempt #1... no vacuum lines were hooked up or ports plugged. Engine cranked good but no fire. Called Cary at GP and he said it definitely won't fire with zero vacuum.

Hook up vacuum lines, and recheck ignition timing. The dizzy rotor is now 180* off from the flywheel BB. Spin the rotor back to #4 cyl.

Attempt #2... cranking is a bit more labored and now back-firing out the end of the header (my exhaust ends there btw)

Call Cary back, tell him what's happening now and come to find out back-firing with propane can damage the mixer. Good to know. Rotated the crank pulley back to TDC to recheck timing, and dizzy rotor is back to 180* off. Come to find out there's a 2:1 rotation ratio between the crank and camshaft. Actual TDC was verified this time by pulling the valve cover and checking the pushrods and valves.

Attempt #3... video! What is happening? How do I fix it? Is the engine trying to divide by zero?
 

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Not sure I know the solution to your problem but I have witnessed the diaphragm blow on a propane mixer due to backfire. That was also on a turbo 4 cyl motor. I'd check the diaphragm if it backfires again.

Have you checked the compression in each cylinder?

Could the cam shaft be installed off?

That's all I got.
 

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Holy crap, I about pissed my pants when that video which was loading in another tab started playing. Freaking volume level 100 :eek::eek:
 

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Discussion Starter #4
Not sure I know the solution to your problem but I have witnessed the diaphragm blow on a propane mixer due to backfire. That was also on a turbo 4 cyl motor. I'd check the diaphragm if it backfires again.

Have you checked the compression in each cylinder?

Could the cam shaft be installed off?

That's all I got.
After the fixes following attempt #2, the backfiring stopped. I'm hoping the diaphragm survived the few backfires.

I haven't checked the compression since it was rebuilt. I could put that on the to-check list.

I don't know any way the cam shaft could be off. When I rebuilt the engine, I left the crank and cam in the block.
 

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What is your battery voltage? Throw more timing at it. I ran my LPG rigs in the mid 30's (total timing)
 

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Discussion Starter #6
What is your battery voltage? Throw more timing at it. I ran my LPG rigs in the mid 30's (total timing)
Up to, and including the first couple cranks last night, voltage (on the gauge) was reading ~12. I didn't think to look at the end of the night.

Could the "lagging" be partly due to an uncharged battery that's been cranking since last Monday? The negative ground was also exceptionally hot, so that's being upsized before any more starting attempts are made.

Forgive me for the stupid question, but how do you measure total timing? Valve plus ignition timing?
 

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From what I can tell of the video the timing is too far advanced and it is kicking back. Remember what I said about using starting fluid too. The equipment is tough but a backfire is like hitting the internal parts with a hammer.
 

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Discussion Starter #8 (Edited)
From what I can tell of the video the timing is too far advanced and it is kicking back.
Good to know.

Remember what I said about using starting fluid too. The equipment is tough but a backfire is like hitting the internal parts with a hammer.
I can't even come close to the point of backfire anymore. That also went away when I found out the ignition timing was off 180*.
 

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Up to, and including the first couple cranks last night, voltage (on the gauge) was reading ~12. I didn't think to look at the end of the night.

Could the "lagging" be partly due to an uncharged battery that's been cranking since last Monday? The negative ground was also exceptionally hot, so that's being upsized before any more starting attempts are made.

Forgive me for the stupid question, but how do you measure total timing? Valve plus ignition timing?
Base + Vacuum/mechanical advance = total timing. Once the engine is running, I run the rpm to 2500 and set the timing using a digital advance light.
 

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Discussion Starter #11
Problem solved! As usual it was something little, like the plug wires being off by one on the distributor. Fired right up and sounds like big 'ol straight-piped titties. Good thing this is a 3 day weekend... I've got a truck to finish so I can go wheeling in a week and a half.
 
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