Ignition breaking up at higher rpm

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funwithfuel

funwithfuel

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Wilmington Il
I put together this little scamp a couple years ago. It has ran great and never disappointed. Now, I'm trying to sell it. Guy shows up, we go for a test drive. It falls on its face. It will idle, won't pull, makes an eerie noise through the exhaust. Not only was this humiliating, it's testing my patience.
It is a 72 Plymouth scamp. It has a 5.9 magnum converted to Carb . I have a Carter fuel pump (electric) mounted low like it's supposed to. Carter 750 AFB . Fuel is filtered at tank sump and after pump.Electronic ignition still using ignition 1&2 .
I thought for sure I had it right out of the gate. Found my ecu loose. Swapped it, polished the mounting and added ground washers. No change. Checked the ballast, loose terminal, swapped w new, no change. Confirm voltage at coil. Good. Check coil resistance. When hot, obtained continuity from primary to secondary winding. Swap with new. Attempt to check gap at pick-up found plate flopping around. Got a reman and dropped it in. Now remember, this thing ran great before whatever happened, happened. Now I'm thinking I was off the mark. I checked the fuel system. Pulled the tank, cleaned it thoroughly. Blew out all the lines. Checked and cleaned pre-screen. Pulled top off Carb, cleaned jets, checked floats , pulled needles and checked springs for bind. It'll start, it'll run it just turns terrible at around 2500 I think. No tach.
Everyone, I know this was kinda rambling but I know you all want what's up and how it's equipped.
I appreciate any help you all might offer. And I won't start another thread on this.
Thanks.
 
Is timing trigger tight on dist shaft?
No wobble?

Is there excess up/down end play on lower dist shaft? Up-down play equals unsteady timing.

Lose a mech advance dist spring?
Flopping weights also confuse engine timing.

How long ago did it run just fine?

Corrosion inside dist cap @ plug inserts?
(Corrosion can be flaked off with a small flat blade screwdriver)
 
I once bought a "new" rebuilt dist with lots of end play, and had your problem, I had to add washers to make sure it spun free, but without end play, which translates into wacky timing at normal loaded rpms as gear/engine reasonance let it ride up and down. Strobe showed timing anything but steady at running rpms.
 
Picked up a reman from oreillys. Really didn't inspect it other than to check the advance plate to make sure it wasn't flopping around like my original was. And checked gap. Got a piece of heavy paper , mic'd at .009" . No brass feelys. Improvised.
It ran great a couple weeks ago, been running good. This one test drive, it just hiccuped and hasn't been right since. Don't like shotgunning parts, I've justified replacement for everything to myself prior to doing so.

Cap, rotor ,wires and plugs all less than 500 miles. Checked wires to make sure they were seated , didn't pull and inspect for corrosion though. Will check in the AM .
All the parts and effort, it's laughing at me, cuz it knows I wanna sell it. It's just being a spiteful ***** , I think.
 
Could be as simple as bad coil wire, an open / broken plug or plug wire, or problems with cap and rotor. AND CHECK VOLTAGE to the ignition. If you can't resolve that part, "hot wire" it temporarily with a clip lead from battery right to coil +. Don't run it that way too long, just to see if it "cured" it

You say you swapped the coil? I would check and change the plugs If you have a tach disconnect it and test
 
Have you checked all the fuel hoses to make sure that they are not kinked? I've seen some kink near the sending unit if not careful putting them on... Also check any hoses with bends near the carb...
 
OK, super embarrassed here. First checked everything for corrosion, all shiny clean. Checked voltage at ballast 12.4
Checked other side 6.64
Checked in crank position, starter disabled 9.45
So far so good
Checked distributor end play .120-.140"

Looked at rotor and bottom of cap. Rotor burned looking where it contacts the coil post. Bent up and polished shiny. Dumb oversight. Took air cleaner off and ran hard full throttle-no load like an idiot. That's when I saw it, the secondaries started closing and the fuel diminished. I was starving for fuel.
Put a gauge on the fuel line 1pound. Fer real? Check all the lines again. All clear.
Reluctantly, I drop and disassembled the Carter pump. Oh my god!!!! The inlet screen was packed with real fine sediment rust. Now , I had cleaned this tank yesterday. Guess I shoulda done it long ago. Road test and all is right with the world.
I appreciate everyone 's input. It made me go back and look at everything I overlooked and all I thought was good. I thank you all.
Just wish I hadn't convinced myself into changing all those parts beforehand.
Live and learn.
Thanks again
 
Here's a pic of the rotor. The way it looked, it's like the spark had to jump from the coil post to the rotor then out to the spark tower. I'm sure this didn't help.

IMAG0378.jpg
 
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