My apologies in advance, this is going to be kind of long...

'76 Dart, 225/833od

After 35k on a rebuild that never ran right (.030 over, engnbldr valves, 9:1 compression, balanced rotating assembly, etc with a 280/270 cam that was never degreed in properly. Super six with a worn out Holley 2300 350cfm, and dual Dutra Duals.) I pulled the motor for a cam swap. Snowball effect ensued, and I replaced all the rings, bearings, etc. and stuffed in a Comp 252. Here's where things get a little interesting. I also ditched the electronic ignition and charging system, for a GM one wire alternator, and a DI special distributor running Pertronix.

Got everything together, and it would idle nicely (with a slight knock), and fall on it's face stuttering, backfiring, etc. off idle. The knock was suggested to be piston slap or??? so out came that motor.

I picked up a "rebuilt" 225 with unknown miles. It had been run with real cheap oil, so I tore down the head, cleaned everything up, and reassembled it with new valve stem seals. Bottom end looked okay, so everything got new gaskets, and put back together. All the peripherals got swapped over from the other motor.

Fired it up today, and it runs just like the last one! The knocking noise was still there, but I ran it up the lift and determined the noise is coming from in the bellhousing. Strange, but whatever. What baffles me is the timing and/or carb issue.

Stock motor internally. 8:1 compression. Valve lash set at 12 and 22 cold. Timing set at 9BTDC, but moving it from 15 before to 15 after didn't make much of a difference (well, 15 after and it would barely run off idle, but it was still stuttering and backfiring the same). It will backfire out of the carb or exhaust interchangeably. My buddy thought it was the dist., so I swapped in the Pertronix dist. out of my fine running truck, with no improvement.

While neither make sense to me, I'm left thinking it might be the carb. is now completely shot (was at least running on the first motor...), or I screwed up the wiring when I gutted the elec. ignition, and it somehow isn't getting enough amps through off idle?

I'll be away from the car for three weeks, but I want to get some ideas going.

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Unless the pertronix took a crap it could be carburator. Unless the alt is completely shot it should provide enough power to keep the mopar EI running happily for a while ( you can run a slant six with stock EI on just the battery for at least an hour before it get salty), but if the module is an 'old one' (i.e. still has the OEM part number stamped on it) it might be on its last legs.

By any chance did you check for vacuum leaks just to rule manifold warpage, or carb gasket/adapter issues?

On the 2300, do you know what model number it is (7448?), what jets are installed, PV, shooter, acc. cam, etc so we have a benchmark to work from?

Pertronix is okay, as I swapped in the distributor and pertronix module out of the truck and it didn't change anything.

Carb is a 7448, not sure on the jets, etc. other than I'm sure they're way off from what they should be... I did discover a very slight vac leak at the base of the carb today, but it was as I was throwing in the towel, so I haven't addressed it yet to know how it was affecting things.

Alternator is brand new. No EI box is prestent, new Pertronix II module.

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This is turning into my new favorite knee-jerk diagnosis, but did you use a piston stop tool to verify TDC on the vibration damper and did you adjust the valves with the motor HOT?

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Casually looking for a Clifford hyperpak intake for cheap.

No piston stop, but I followed the procedure in the Factory Service Manual with a dial indicator on the #1 intake spring retainer and the timing mark was spot on. Also, playing with the timing in either direction didn't change the symptoms, so I think I can rule that out.

Haven't adjusted the valves hot yet, but it won't change things that much.

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It probably shouldn't matter, but a one-wire GM alternator setup is not a good solution. It will not give consistent voltage, as it won't sense the voltage in your system as a 3-wire setup will, it only senses what comes out of the alternator. The Pertronix may demand a stable voltage, you should measure the voltage to the ignition, just in case. It also draw a great deal more current than the Mopar ignition.

You should also upgrade the Dart's electrical circuits, if you have been running a stock mopar alternator earlier. If you have a larger output from the new alternator that from the stock one, you MUST do some wiring upgrades!
I have recently rewired my Aspen (under hood only) for a 3-wire 105Amp GM 12si.

Olaf

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Aspenized

Now now don't let your head get to big. lol. You did help me but in my defense this is my first ever rebuild/new engine/cam swap etc etc etc.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

Since it's a '76 and uses a shunt, the only thing that changes in the factory wiring diagrams is the alternator main black wire would upsize to 8 or 6 gauge, and the voltage regulator would need to be swapped out for the appropriate version depending on alternator choice (65 amp, 100 amp).
(The only other upgrade that doesn't count here is the added 12 ga black wire with fuseable link that runs to the rear heated widow relay...)

-D.Idiot

Okay, I'm back to playing with the car. I got a brand-spanking-new Holley 2300 (7448), jetted it with 58s, and roughed in the mixture. Still backfiring out both ends. I noticed I might have an exhaust valve too tight, so next time I'm at the shop I'll try to go over them with the car running. I'll try to sketch out my wiring mods to see if you guys catch something I overlooked.

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