Is there a way to tell the difference between ignition points that are bouncing vs. fuel starvation?
Is there a difference in the symptoms?
Breaks up at 2500-3000RPM on hard acceleration;looses power; no problem when driving normal.
Thanks,
Kurt

 

From my experince, I would say that 2,500 to 3,000 rpm is NOT hard enough acceleration to cause the points to bounce or float. Maybe it is more of a fuel or spark plug wiring problem? Possibly a weak coil?

 

Point bounce usually occurs at higher RPM's than where your problem lies. I would be looking at the usual suspects: Wires, plugs, timing, vacuum advance, coil, accelerator pump, fuel filter. Wouldn't hurt to throw in new points ( I like Accell) and make sure the dwell is around 30. You could check float bowl level but it doesn't sound like that to me. Good luck

 

Kurt,

I had the same problem with mine cutting out under hard acceleration at about 3200-3500 rpm. Turned out to be a problem with my air cleaner. The cover plate was getting sucked down to far because the element wasnt tall enough. After going through the ignition parts and checking fuel flow, we noticed a little dent in the air cleaner cover. Pulled the cleaner and did a test run. Ran great. Now I'm looking for a BB hood.

 

What kind of carb do you have?

 

How old is the dizzy and haa it ever been rebuilt? If there is a bunch if bushing play, especially in the upper bushing stability of the points may fluctuate as RPM's increase.

One sure fire way to tell this is to check the timing curve. Put the timing light on and starting at idle, gradually increase RPM's while watching the timing mark advance. If the timing appears to be erratic with the mark bouncing back and forth as you increase RPM's this could be the culprit. I had this issue and solved it with new HEI! My breakup was in the 4-4.5k range but exact same symptoms.

Good luck!

 

Kurt,

As most have stated, point bounce will not occur at the low RPM’s you describe.

One quick way to test the distributor in the car for a bushing problem is to stick your dwell meter on the car and rev up the engine. If the dwell opens up when you raise the RPM’s then you have a bad upper bushing in your distributor.

You might look at the distributor cap and check it for a carbon trail (crack). Check the rotor condition, check the wires on the condenser and make sure it is not breaking or is not rubbing anything too.

Coil could be a possible culprit, plug wires arching on the ignition shielding, or a wire just breaking down.

I’ll assume it will break down when rev it without a load so a quick cheater trick to look for fire jumping would be to lower the garage door and turn off the lights with it running.

Willcox

 

Thanks all for the input.
Lots going on right now so finding time to play with the car is tough but I will try the suggestions provided by everyone as soon as time permits.
It's a 68 and everything is new and factory original, no modifications, so it is the stock carburetor completely rebuilt and tested by Lars, new wires, new plugs, correct air filter motor has less than 2,000 miles on it. Distributor was reworked by machine shop and everything worked perfect last summer for the 500 miles I drove it. New coil, points, rotor, distributor last year but something could have gone wrong this year. It started about 3 week ago when I last drove it. Changed out all the gas, new fuel pump, etc
Might be that damn fuel pickup sock in the tank, or could be I got some bad gas.
I'll check everything again.
Thank you everyone,
Kurt

 

Gkull,
Carburetor is Rochester # 7028219 completely rebuilt and tested by Lars on this forum
Kurt

 

I'm assuming you mean the car sputters at WOT at 2500-3000. In my experience this is usually a problem with the air fuel(carb, fuelfilter, fuel pump, accelerator pump, float level in carb too low) or plug wire(s) shorting, or poorly gapped plug(s)

Since everything is new, check for things that need adjusted.

This rpm range is too low as stated above for point float, also too low for lean surge.

BTW, do things clear up after 3000?

 

As already mentioned, points 'float' at moderate rpm levels is unlikely, unless the points set is damaged or really poorly designed/made. Your problem is most likely an ignition problem, a fuel starvation problem, or a valve train damage issue.

If you have a garage, put the car in at night, open hood and start it, then turn the garage lights off and look at the ignition components (distributor area, coil, plug wires, plugs) for any visible arcing/sparking. That would indicate that the spark signal was bleeding off and not firing the plugs correctly. Certainly, worn/pitted/improperly adjusted points could cause your symptoms as well. You can remove your valve covers to check for any valve spring problems/damage. If there was a 'gross' problem with the valve train, it wouldn't even run properly at idle...let alone at 3000 rpm. But old/weak springs or a cracked spring could also produce such symptoms.

Separating the fuel supply and the ignition system as possible culprit areas can be troublesome. Without knowing that one or the other is working properly, you can't rule out either one as the cause. And fuel supply faults can be due to tank/line blockages, pump problems, filter restrictions, and/or carb issues.

First look for any cracked, pinched, or damaged fuel lines anywhere between the fuel tank and the carb. The rubber lines [ahead of the fuel pump] are usual suspects for a fuel supply problem. Then make certain that the distributor is well grounded. The distributor body casting needs to make electrical ground with the engine block via the metal retaining clamp; so the contact points on the bottom of that clamp, as well as the block and dist. housing where the clamp contact, need to be free of any paint so that electricity can flow. Lastly, check the signal feed wire in the dist. for continuity and that it does not short out to ground when you move it around. All of that stuff can lead to a weak/intermittant signal to the plugs.

If nothing there, then my approach would be to swap components until improvement was achieved. If you buy replacement parts and changing them has no effect, you can keep the removed part as a 'good' spare for a later time. The order of changes which I would make are:
fuel filter; points/condenser/rotor (as a set...too much trouble one-at-a-time); distributor cap; coil; plug wires.

Good luck. All of us suffer with this same kind of problem eventually.

 

Also check the gas tank is venting (drawing in air to replace gas geing used).

 

Also check the gas tank is venting (drawing in air to replace gas being used).