So, I just bought a Camaro, an 86 with a mildly modded LG4, computer controlled carb and ignition. I developed a problem almost immediatly driving it home. The car will skip, miss, and cut out under light to medium heavy loads at any rpm under 2750. Once you climb over that, it runs fine, but hits a brick wall at about 4500rpm, only in third, first and second pull fine to 5500 where I shift.

I'm fairly positive this is an electical problem, because even with a light mis-fire, I get a pretty good bounce/drop on the tach, like 500-1000rpms difference, and this is with the TC in lockup, so its not really dropping that much. Here is where it gets even wierd-er, when I put more load on the electrical system, the problem is less prevelent. Especially at lower speeds, going around town, it almost goes away completely with the headlights and defrost on. Turn them off and it goes right back to it. Gets worse as soon as the TC locks up and stops drawing voltage.

So, any thoughts, idea, things to try? I appreciate anything you all might have for some ideas as to what this is.

 

Here is an update, I'm positive the 4500rpm fall on its face isn't anything to do with the spark, its a pretty repeatable thing, its gotta be low fuel pressure. I experimented a bunch tonight, and it'll fall off after 5ish seconds of WOT in any gear, just won't go until you life of the pedal, and give the carb a second to fill up with some more fuel. If I just hold third and go at it 3/4 throttle, it'll pull right past 4500 as far as you wanna go. So, I'm guess its time for a new filter, or hopefully not a new fuel pump.

The lower rpm skip/mis/stumble is still as real as ever. Gonna have to get out the volt-meter and figure out whats going on. Still, I'd appreciate any thoughts, its real wierd how it'll calm down if I load the electrical system. Can't figure that one out...

 

No thoughts from anybody huh? I'll continue to update anyways, maybe somebody will jump in. I took a good look at the distributer, a DUI unit. I couldn't find any loose connections or wires out of place. I'll say this, there certainly is a lot of crap under the hood of a C.C. carb car.

I took it out again, I still have the fairly regular lower rpm miss with major tach jumpage. The high rpm bog is gone, for the moment, pull right up to 5500 now, its pretty fast for an LG4, the pervious owner did a nice mild build on it.

 

Attach a ground wire from the valve cover or engine block to the fire wall.

 

I'll give that a shot. Whats the logic behind that?

 

Not real sure why this works but it worked on my car.
Unless there is a ground wire running from the motor to my firewall, the engine will miss when you snap the throttle.
When the ground is connected the motor runs fine.
Let me know if this helps you.