RPM's cut our holding speed

[Erik1371]

I'm new to this so bear with me, I have a 72 k10 with the original 350, edlebrock 1406, the original distributor with an ignitor kit and coil and freshly rewired truck. The problem is when I hold speed above 45 it will stutter for half a second, rpms drop about 1000 and come right back up, I can rap it out to 4000 rpms with no problems it only does it while maintaining speed. Sometimes it does it 2or3 times in about 10 seconds, sometimes once every few minutes and sometimes not at all. Any Ideas?

[70']

You mentioned "freshly wired". Your problem is electrical, most likely a loose or shorting out wire. Go back through all the ignition wiring and recheck all your connections and look for shorts

[toolboxchev]

X2 electrical

[Killer Bee]

what type of distributor module, pertronix? rev limiter? set properly?

sounds like the work was hired, what does vendor say about it?

[geezer#99]

What intake?
What headers?

[BigBird05]

How many miles are on the distributor? The shaft and bushings wear out. Check all of your grounds.

[68 P.O.S.]

What's your timing set at? Any vacuum leaks? Condition of fuel filter, lines and pump?

[Sheepdip]

You got a exhaust lobe on your cam going flat. Hate to be the bad news guy.
What's happening is since it doesn't fully open the spent gasses aren't being fully scavenged out of the cylinder and eventually you get a less that stellar air/fuel ratio so it stumbles just like a performance cam at low rpm.

[MySons68C20]

Originally Posted by Sheepdip

You got a exhaust lobe on your cam going flat. Hate to be the bad news guy.
What's happening is since it doesn't fully open the spent gasses aren't being fully scavenged out of the cylinder and eventually you get a less that stellar air/fuel ratio so it stumbles just like a performance cam at low rpm.

Imho if it was a flat cam the problem would persist all the time. The sporadic nature of the problem points to electrical gremlins and possibly fuel delivery issues.

['68OrangeSunshine]

I had a Pertronix Ignitor II that did that. It would completely kill the ignition at freeway speeds.
Burned out module.
I sent mine back to Pertronix for evaluation. Still waiting for an answer, about 5 years later.
Solution: genuine GM HEI.

[Ironangel]

Originally Posted by '68OrangeSunshine

I had a Pertronix Ignitor II that did that. It would completely kill the ignition at freeway speeds.
Burned out module.
I sent mine back to Pertronix for evaluation. Still waiting for an answer, about 5 years later.
Solution: genuine GM HEI.

This and yes by all means get an HEI dizzy and drop in that thing...

[Erik1371]

Thanks for all the insight, I did wire it myself and all the connections look good, engin is original and it's getting a roller 350 put in it in late spring early summer (just hope it gets me through winter) and it is the original distributor with about 60 thousand miles so that's getting replaced with the new engine, original style exhaust manifolds and intake. It will all be better in about 6 months when it all gets changed. Thanks again for the insight.

[toolboxchev]

First thing I would do is pull the distributor cap and clean the entire dist with carb clean.

Of course you will have to pull some of it apart. Second disconnect the battery before doing anything.

[3767]

With a meter u could check your coil. This will tell u if your coil is still in spec. Check the resistance. Then check your plug wires 1 at a time. Same reason.