Well, I'll repost this one. Maybe someone happens to have had the exact same experience and can help. I'm tiring of throwing $$$$$$$$$ at every little problem only to have it not exactly fixed and then throw more $$$ at it. I've got about $60,000 in this one and it's not even perfect yet.
Okay, when pulling from a stop, under light to moderate acceleration, everything is fine from 600-1300 rpm. Then, at 1400 rpm, it stumbles hard. Then, it comes back to life and all is fine from there on. It stumbles so predictably and suddenly, I am almost certain there's just a spark cutoff. If the engine is cold, it will often stall completely. If I accelerate very gradually, it doesn't happen. If I ROMP on it, all is fine with no stumble. This is not the same "stumble" you get when you jump on the throttle and it bogs for a second because it's become too lean for a slplit second. This is a different thing. I'm pretty sure it's spark.
This also will happen on the freeway cruising at say 75 mph. It seems like I just get back in that "stumble zone" where it just wants to die. If I accelerate, it clears up. It also seems to be worse the longer I drive on the freeway .
Now, based on this, it seems like there is just a dead spot which comes on at a specific load and/or maybe vacuum. Here are some of my suspicions:
* Vacuum advance screwing up: unplugged and capped the tube but the problem remains the exact same. That's not it.
* Coil: The coil is an el cheapo from Pep Boys. The original coild cracked just a few weeks ago and I replaced it with a $15 OEM model. The ignition is Pertronix electronic. Could driving with the old cracked coil have damaged the pertronix ignition? Could the new coil not be working with pertronix electronic?? (I don't know if the electronic ignition requires a coil upgrade??)
* Pertronix Ignition: See above. Could it just have a dead spot where no spark is being thrown at all?? It seems to be load or vacuum specific problem and happens even with the vacuum hose disconnected and capped.
Details on this engine:
> 224/230 @.050 cam with 110 LSA
> Deamon 525 cfm carb with vac secondaries and electric choke
> Guages: all new electronic (I only include this b/c I've heard of the electric tach sometimes creating a problem / short in the ignition system)
> Dual plane manifold with 2" spacer
> No vacuum leaks
> Just spent like $500 on a tune from a pro tuner (old hotrod guy here in LA). I don't think he's leaned it out too much. Also, the plugs are nice tan color.
Guys, I'm stumped.
Okay, when pulling from a stop, under light to moderate acceleration, everything is fine from 600-1300 rpm. Then, at 1400 rpm, it stumbles hard. Then, it comes back to life and all is fine from there on. It stumbles so predictably and suddenly, I am almost certain there's just a spark cutoff. If the engine is cold, it will often stall completely. If I accelerate very gradually, it doesn't happen. If I ROMP on it, all is fine with no stumble. This is not the same "stumble" you get when you jump on the throttle and it bogs for a second because it's become too lean for a slplit second. This is a different thing. I'm pretty sure it's spark.
This also will happen on the freeway cruising at say 75 mph. It seems like I just get back in that "stumble zone" where it just wants to die. If I accelerate, it clears up. It also seems to be worse the longer I drive on the freeway .
Now, based on this, it seems like there is just a dead spot which comes on at a specific load and/or maybe vacuum. Here are some of my suspicions:
* Vacuum advance screwing up: unplugged and capped the tube but the problem remains the exact same. That's not it.
* Coil: The coil is an el cheapo from Pep Boys. The original coild cracked just a few weeks ago and I replaced it with a $15 OEM model. The ignition is Pertronix electronic. Could driving with the old cracked coil have damaged the pertronix ignition? Could the new coil not be working with pertronix electronic?? (I don't know if the electronic ignition requires a coil upgrade??)
* Pertronix Ignition: See above. Could it just have a dead spot where no spark is being thrown at all?? It seems to be load or vacuum specific problem and happens even with the vacuum hose disconnected and capped.
Details on this engine:
> 224/230 @.050 cam with 110 LSA
> Deamon 525 cfm carb with vac secondaries and electric choke
> Guages: all new electronic (I only include this b/c I've heard of the electric tach sometimes creating a problem / short in the ignition system)
> Dual plane manifold with 2" spacer
> No vacuum leaks
> Just spent like $500 on a tune from a pro tuner (old hotrod guy here in LA). I don't think he's leaned it out too much. Also, the plugs are nice tan color.
Guys, I'm stumped.