Hmmmmm, still thinking out loud.

''A while ago during this odyssey I tried manifold and the engine wouldn’t start. ''

It makes sense that if it doesn't start on ported, it won't start on manifold either.

''Of note: the backfire has changed with the dizzy replacement. It was doing it at around 1800 RPM. That’s gone. Now it’s when the advance can is connected and throttle applied.''
''I know it works. I applied vacuum and watched the advance move with the cap off.''

The engine runs smoothly and without issues with no vacuum advance connected. (I didn't see any comment stating backfires when revving when the advance is connected.)

That sort of tells me that the module and coil are ok, and that we're back to inside the dizzy, and back to coincidence.

Seeing as one has to remove half of the internals to get to the springs and limiters, what's the chances that during assembly, a screw, or something, has been fitted in such a way that when vacuum is applied, the vacuum arm is somehow interfering with something else ?

I know that sounds like a dumb question, but maybe it provokes new thoughts.

 

I’ll be back with the result after replacing the module. It’s supposed to arrive today and hope to get back on things before leaving for deer hunting Thursday afternoon.

 

Oh FFS, that's the second time I've written crap. Sorry !

The bold underlined part should have said not connected.

I had read post 52, and understood it to mean backfiring only after the vac advance was connected.

Is this an accurate summary ? :

With no vacuum advance connected :

The engine can be timed reasonably accurately.
The engine idles and revs problem free.

It's probably a waste of time trying to start with ported vacuum attached seeing as we know it will run crap anyway once fired up.

If it runs crap with ported, then it's highly likely that it would also run crap with manifold advance.

If you say yes to the summary being correct, that leaves the issue somehow only with the vac advance canister and/or a leaking hose.

Ok, I'm very keen to see if the module replacement fixes the problem, so I'll shut up and wait for the result.

 

Yes, summed up well

 

Do you ever hear a song that is soooooo sh$t, that it sticks in your head, and you can't get rid of it ?

Well, this thread kinda reminds me of that scenario. LOL

On that note, still thinking out loud :

If you were able to run the engine at idle with manifold advance, you'd probably see timing at +/- 36* (16* idle + 20* say, advance)

You actually started your engine previously at 40* +, so that suggests, in addition to the recent summary, that the existing module works fine.

So I'm going to revisit my fixation on 'coincidence'.

Another summary :

The engine ran fine.

The dizzy was taken apart and springs changed.

Suddenly 'Houston we have 2 problems'.

The new dizzy fixed 1 of the problems, and the 2nd problem, being the vacuum side, remains.

If the new module solves the problem, great, thread closed, and nobody cares anymore.

But ! If it doesn't, try and see if you can tell how the new dizzy fixed the 1st problem by comparing it to the OE dizzy. (That would be very useful info.)

The vacuum issue, problem 2, remains on both dizzies, so that can't be compared.

Maybe set the idle timing to 36*, and rev it a bit. I don't think there will be any backfiring.

If no backfiring, I would open the dizzy and really have a good look at the canister mechanisms.

I don't think a hole in the dizzy hose is causing the backfiring, but I'd still look for a hole/tear.

Now I'll definitely shut up and wait !

 

Please don’t! Shut up that is. I’m under the hood as we speak. I checked the vac advance again. I put vacuum on the hose while connected to the can and it holds 15” vacuum. The advance starts moving at about 2” and reaches the limit at 11”. No issue here.

I was just checking to see if the can is adjustable and lo and behold, it is. I am going to start research on how to adjust it when I don’t have the old one to match up.

Any new thoughts??

 

Just as I got the annoying 'Girlie' song out of my head, and replaced it with a live version Of 'Smoke on the water' by Deep Purple, you posted post 66, and the Girlie song is back.

So my new thought is why did Go Seahawks! post 66.

Don't worry about adjusting the can at this stage as it is not important right now.

The can holds vacuum, but is there any chance that while the arm is pulled by vacuum, the arm, or 'something', is getting in the way of 'something' else ? (Yup, I think this is a dumb suggestion.)

I know you said that everything moves freely, but I can't help continue fixating on the vacuum can.

The only question we seem to have is, ''Why does the vacuum advance cause problems?''. (I don't have an answer. )

Yes, 36* idle.

By setting it to 36*, and revving up to 2,500 rpms only, or whatever the backfiring rpm is, we'd be simulating manifold vacuum attached, to an extent.

Then set it back to 16* after that test.

If it doesn't backfire, we're back to a vacuum issue only.

If it does backfire, hmm, ok, that will mean 'something'.

I agree that the catching of the wires by the reluctor shouldn't have done damage, unless the actual wires within the casing got damaged, which is unlikely.

I would expect damaged wires to give problems whether vacuum advance is damaged or not, but that is not the case, and besides, the exchanged dizzy solved the problem. (Although we'll never know how. )

The backfiring is still bugging me.

Is the dizzy hose perfect ?

Would you have enough hose to connect the dizzy directly to the intake manifold or rear of the carb (pcv port maybe ???) ?

Retarded timing or a carb problem could cause backfiring, so connecting directly to the intake manifold would bypass the current carb fitting.

I don't think it's the carb either, but quick 'n easy tests will give us valuable information at least.

Or, the new module fixes everything ! (Although I can't see how vacuum advance is related to the module.)

 

Go ahead and see if the engine will start with the vacuum advance connected to ported.

This will tell us something although I don't know what ! LOL

Still thinking.

If the vacuum advance arm was somehow preventing the mechanical advance from advancing, which has been my thinking until now, it shouldn't make a difference.

I've started my truck before with 2* advance only.

I'm out of ideas.

 

may be time for some pics/videos of the situation.

 

Since there seems to be a digression let's go from 66 to 55
Ol' 55'

 

You talk about digression, get this: the backfire at 1800 RPM with vac advance plugged is back. And I now have a spare spark control
module. Here’s the chain of events today:

I researched vac advance adjustment. There are 16 turns lock-to-lock with my can. Mine came to me out of the box at 2-1/4 turns out, meaning it was pretty sensitive and added advance with minimal vacuum signal. I turned it out to the mid-point, 8 turns, as a starting point.

Vac Advance Disconnected: 850 RPM idle. I replotted the advance curve with 16* initial and measured 25* at 1500, 28* at 2000, and 31* at 2500. These stayed consistent with subsequent confirmation measurements taken during subsequent timing tests. I started noticing a smallish backfire beginning around 1800 RPM @ 27*. It disappears completely by 2000 RPM and doesn’t come back. This issue has now been common to both dizzys.

Vac Advance Connected: it will start with advance connected and it will run up to the 1700-1800 range when the backfires start. These are quite a bit bigger and louder than when the advance is disconnected, and I can’t throttle up through it like I can when advance is disconnected. It gets worse. Also, the light on my timing light starts flickering and then goes dark during the worst of the stumbling and backfiring. This is the first time I’ve seen that. As I’m slowly throttling up from an idle and approach the trouble speed, I can hear a misfire begin. It’s not as pronounced when advance is disconnected.

So it seems when I adjusted the vac can for less sensitivity I just chased the stumble/backfire problem up to a higher RPM.

I did not perform tests with 36* initial since the problem is not isolated to the advance can, however, the can does accentuate it.

I’m ready to go hunting.

Sending everyone calming thoughts of melodies by Led Zeppelin, Dire Straits, Eagles, Rush or whatever kinds of sounds you groove to…

 

If anyone want to see anything let me know.

 

I forgot to add, it will start with full manifold vacuum connected to the advance but it backfires and will only run by continuously working the throttle while it’s snorting.

 

LOL @ the digression.

Thank you for the Led Zeppelin etc melodies.

I managed to hear the start of the guitar rift towards the end of the song 'Stairway to Heaven', but suddenly went deaf.

Therefore, writing 'thinking out loud' won't work coz I won't hear anything.

Problem solved. I went to the shops and bought straws.

So, grasping at straws, here goes :

I finally agree with you that the vac advance is not an issue at all, it works just fine, but simply accentuates the backfiring.

The timing curve numbers reflect a perfect linear curve. Nice ! (This proves that the dizzy is working as it should in that area.)

When you initially worked on the dizzy, the only other parts that you would have touched, are the HT leads.

Maybe, just maybe, the metal part in one of the caps somehow broke or came loose. It's a 5 second check too see what's what. (Yeah, LOL, definitely grasping at straws.)

Is this the replacement dizzy that you got ? :

https://www.rockauto.com/en/moreinfo...AlII%2FA%3D%3D

If yes, then maybe you did in fact damage wires after all, and the original electronic module is suspect.

I doubt that the original rotor or cap got damaged, but that's also a 5 second check.

Where the plug from the dizzy connects to the plug in the wiring system, is that 100% clean ? (Yeah, that's really grasping at straws !)

I wouldn't mind seeing a picture of the Ranchero.

Next time you post, please type loudly so that I can hear what you are saying.

 

Hoo boy. Now we’re rolling. I’m starting to feel like Ozzy on that Crazy Train

Another thing yesterday I alluded to but didn’t clarify is that the new module arrived. There was zero change after it was installed, hence I now have a spare.

Here’s the distributor I bought:
https://www.rockauto.com/en/partsearch/?partnum=D4006

Grasping at straws and thinking outside the box is somehow going to yield the answer, eventually. I’ll look at the things you’ve suggested. It may not be until I get back early next week. I’ll post up again when I do.

In the meantime here’s a handful of photos of the green beast that’s been taunting me.