Big Cap Dizzy Install on a 1.5F

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GregRay

GregRay

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Recently picked up a "big cap" dizzy, matching coil/ignitor and dented side cover that I plan to install on my '74 40 some time soon. I've read a few threads and have a pretty good idea what to do, but have a few questions.

1. The two vent holes on the distributor cap -- I have no place to run lines to -- should I just leave them open to vent or should I cap them?

2. The main vacuum advance port (the one closest to the distrib. body) -- should I run the vacuum line to the port on the top of the intake manifold (where the line on my current stock '74 distrib. goes)? Or to the base of the carb (I have a Weber 38/38 that came with the truck, which has a vacuum port on the bottom that I've never used).

3. The secondary vacuum advance port (which I think is the high-altitude one) on the outside - should I just cap this?

Thanks in advance
IMG_4386.webp
 
I just put my big-cap dizzy in a couple weeks ago. My vents are still open. Do not cap them. I plan on running some vent tubes similar to the 60...one port to a filter and one port to light intake vacuum. The whole point of those vents is to prevent flammable fumes from collecting inside the dizzy cap and going boom when you turn the key.
I hooked my inner advance diaphragm to the ported vacuum at the base of my carb. do not attach it to manifold vacuum. Outer one is still open.
Runs fine, maybe runs a little easier at higher RPM than the '69 dizzy with Pertronix did.
 
I thought the vents were to draw air through the dizzy to dry out any moisture

one connects to a light vacuum and the other to a filter in the cabin (at least on a 40).
 
erics said:
I thought the vents were to draw air through the dizzy to dry out any moisture

one connects to a light vacuum and the other to a filter in the cabin (at least on a 40).
Click to expand...


Actually that is correct, but mostly it vents ozone produced by the electronics in the dizz.
 
Well, a month and a half later, I've finally got the big cap dizzy installed and the coil/ignitor installed. Problem -- won't start. I've followed this old thread:
https://forum.ih8mud.com/40-55-series-tech/413723-dizzy-hookup-electrical.html

and read several others and think I've got everything connected right. Bear with me, since electronics are not my strong point.

With the ignition in the run position, I have 12v power to the positive side of the coil; although, for some reason if I put the negative lead of the multimeter to the negative post on the coil (instead of on another ground) , the voltage drops to zero. Starter cranks the engine fine and fuel is getting to the carb. The coil checks out. I thought I might have a grounding problem with the coil/ignitor, so I ran a ground wire from the coil bracket to the negative post on the battery, but that didn't make a difference.

So, the question is, what should I check next? I'm assuming I either have a bad connection, or there is a problem with the ignitor? Is there a way to check the ignitor with everything installed?

Thanks.
 
Are you still using the original style starter solenoid and wiring? or have you by-passed all that...
 
Pighead,

Good question. I installed a new starter about a year ago and didn't change any of the original wiring at the time. The only change to the vehicle wiring for this install was to connect the B/Y wire to the power lead on the ignitor. I have verified that I have 12V at the B/Y wire and, after the connection, at the + terminal on the coil. I did have to splice in an extension piece to the wire that runs from the ignitor to the dizzy as well, but I used shielded wire and I don't think that is the issue.

Should I bypass the original starter wiring? If so, how?

Thanks.
 
No, you don't need to bypass the starter wiring. It gives a momentary 12V to the coil during "start" only, then in "run" it routs 12V to the ballast resistor which cuts the coil voltage down to 6-9V. Surely you do not have a ballast resistor in the circuit anymore. I don't think electronic dizzys like anything <12V.
 
Correct, there is no ballast resistor -- it was removed when I installed a Pertronix unit in my original vacuum retard distributor.

I'm really at a loss as to what to try next. Given that I have power at the + terminal on the coil, is it likely that the problem is in the ignitor? Or the dizzy itself? I bought the dizzy/coil/ignitor as a package from a MUD member who assured me they were all good, but you never know for sure.

I hate to go back to the old vac. retard dizzy (since the main point of this "upgrade" was to switch to a vacuum advance distributor), but it may come down to that soon if I can't get it to fire up in the current configuration.
 
One more question for the electrical experts: I'm trying to determine if the lead from the ignitor to the distributor is the problem (since I had to splice an extension piece into it). With the ignition in the run position, should there be voltage at the positive side of this wire?

Thanks again.
 
Well, I did the "battery test" of the lead wire from the ignitor to the dizzy. Got a good blue spark at the coil. So, it appears that the lead wire isn't the problem either.

Still at a loss as to why I can't get ignition.

Thanks for any suggestions.
 
GregRay said:
Well, I did the "battery test" of the lead wire from the ignitor to the dizzy. Got a good blue spark at the coil. So, it appears that the lead wire isn't the problem either.

Still at a loss as to why I can't get ignition.

Thanks for any suggestions.
Click to expand...

Are you sure that your rotor in you dizzy is touching the contact in the center of the dizzy cap cuz that could do it
 
Thanks. I installed a new rotor before installing the dizzy, but I'll check to make sure.

At this point, I think I've checked everything in the coil/ignitor/ and related wiring, so I'm beginning to think there may be an issue with the dizzy itself.
 
Still no ignition!

Based on the tests I've done, I think(?) I've narrowed it down to a problem in the dizzy itself. Is there a way I can test for a bad pickup coil without removing the distributor?

Thanks.
 
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