1968 Charger has me stumped

danf_fl · Nov 28, 2018

Engine misses at 35 mph and carb backfires on acceleration.
Plugs, wires, dist cap, rotor are new.
I replaced points with a module and changed the coil (and ballast resistor for fun).

It's a 383 changed to 4bbl with a mild cam. Bored 0.40 over, flat top pistons.
Heads have hardened seats to run unleaded.

Compression is good. Fuel tank, sender unit replaced.

Too much fuel from carb?????

What could I be missing?

Bill Monk · Nov 28, 2018

Did you have the problem before the tune up? What is your timing set at?

Daves69 · Nov 28, 2018

Was it missing before with points?
Make absolutely sure your wires are correct. 5 & 7 are easiest to mix.
Visually inspect the cap inside too for issues.

danf_fl said:
Plugs, wires, dist cap, rotor are new.
I replaced points with a module and changed the coil (and ballast resistor for fun).

What's "a module"? Probably should expand on this a bit.
Because it's new doesn't necessarily make it good.

khryslerkid · Nov 28, 2018

When did this start, after the cam and carb change?

Three inquiring minds want to know!

danf_fl · Nov 28, 2018

This is the module to replace points. I also have the coil suggested to go with it.
https://www.classicindustries.com/product/1968/dodge/charger/parts/px91381a.html

This engine has had the problem before the block was replaced less than 200 miles. Rebuild did not remove the problem. So I replaced points and coil. Should I be looking at fuel? I hate throwing money in this without a solution, but the "voices" (or so called experts) keep saying "this should fix the problem...." only to go down the wrong path again. Compression is good. I have only the distributor and power brakes on vacuum (heater and headlight door actuators are disconnected and capped to reduce possible problems)

threewood · Nov 28, 2018

Distributor mechanical advance free and moving inside? Is the vacuum advance in good shape and holding vacuum?

danf_fl · Nov 28, 2018

Thanks. I have to look at that.
It may be cheaper to replace distributor than repair.

Bill Monk · Nov 28, 2018

danf_fl said:
This is the module to replace points. I also have the coil suggested to go with it.
https://www.classicindustries.com/product/1968/dodge/charger/parts/px91381a.html

This engine has had the problem before the block was replaced less than 200 miles. Rebuild did not remove the problem. So I replaced points and coil. Should I be looking at fuel? I hate throwing money in this without a solution, but the "voices" (or so called experts) keep saying "this should fix the problem...." only to go down the wrong path again. Compression is good. I have only the distributor and power brakes on vacuum (heater and headlight door actuators are disconnected and capped to reduce possible problems)

Need to know what your timing is set at (initial with vacuum advance disconnected and plugged) also you mentioned changing the ballast resistor, somebody correct me if I'm wrong but I'm pretty sure the pertonix ignition doesn't use a ballast resistor

danf_fl · Nov 28, 2018

Supposedly it works with the stock system.
I am using the same distributor from before block replacement and I don't know if it was good to begin with.
Car was purchased over 20 years ago and I don't know what my step father did to it over the 20 years he had it. I'm just trying to clean things up.

khryslerkid · Nov 28, 2018

Don't keep throwing parts at it in hopes that it will fix the problem. Do proper diagnosis on each item that might cause this, to make sure they're not faulty. Think simple first.

Attach a timing light and check proper timing. Then watch what it is doing throughout the rpm range to check advancement. Check for a good spark at the plug wire.

Check carb settings and make sure it's not too lean. Pull spark plugs and see if they are burning lean. If so, maybe remove top of carb and check for dirt/sediment in the float bowl. If so clean and replace fuel filter also. If things look clean, make sure there's no water in the fuel. Check fuel pump operation for good pressure.

There's many things to check that doesn't cost money. Do all of these first.

danf_fl · Nov 28, 2018

Thanks, but being as cheap as I am, I already crossed those roads.
I had to replace fuel tank and sender, and replaced fuel.
The carb is an Edelbrock 650 off the shelf with not mods.
The distributor was working with the original 2bb before crank bushing failure.
Took advantage to go to 4bbl

danf_fl · Nov 28, 2018

Yes, timing is dialed in at 5 degrees BDC and moves as engine speed changes.

Don Frelier · Nov 28, 2018

danf_fl said:
Yes, timing is dialed in at 5 degrees BDC and moves as engine speed changes.

A couple ideas/suggestions:

Is it set for 5 Degrees with Vacuum advance disconnected? (I would try 10-12)
- Test Advance with and without canister connected to ensure the vacuum advance is working properly

Float level?

Is the exhaust system restricted by any chance?

Bill Monk · Nov 28, 2018

danf_fl said:
Yes, timing is dialed in at 5 degrees BDC and moves as engine speed changes.

advance your timing to 12-14 btdc. If you have a vacuum gauge, connect it before you advance, the highest reading should be close to where you want to be. Test run it there and see what you have and go from there but you do need more timing

danf_fl · Nov 28, 2018

I capped the headlight vacuum system off at the manifold. Is that the canister you meant?
5 BDC vacuum disconnected and vacuum advance seems to work.

Bill Monk · Nov 28, 2018

danf_fl said:
I capped the headlight vacuum system off at the manifold. Is that the canister you meant?
5 BDC vacuum disconnected and vacuum advance seems to work.

no, the vacuum advance can attached to the distributor. unplug and cap it when setting initial timing, looking for the highest vacuum reading but likely between 12-14 btdc

danf_fl · Nov 28, 2018

Thanks, I will try 12-14.

PurpleBeeper · Nov 28, 2018

My 2-cents...
a. follow Bill's advice on timing starting at maybe 12 degrees before top dead center. You want to disconnect & plug off the little hose going to the distributor. Also, rev the engine up while you're at it to about 2500-3000 rpm & watch the timing. We would like to know what the maximum timing advance gets to & "about" what rpm that happens at. You don't want more than about 34-36 degrees when revved up.
b. TRIPLE check that each plug wire is going to the correct cylinder & in the correct order. Remember, big block mopars' distributors turn COUNTER-clockwise. The cylinders are numbers 1-3-5-7 front to back on the driver's side & even numbers on passenger side.
c. What do you mean "crank bushing"? Bearing?

Daves69 · Nov 28, 2018

How did/does the distributor internals look?
Can you verify both mechanical advance springs are intact?
Lubrication basics...…
https://www.forabodiesonly.com/mopar/ams/how-to-properly-oil-advance-cam-in-a-distributor.149/

just for reference...….

danf_fl · Nov 28, 2018

Thanks, I was having a "brain fade" when I said "bushing". I did mean bearing.

1968 Charger has me stumped

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