Won’t rev past 2000 rpms

[Cu1n81]

Hey guys,
First post here. Just bought a 1979 C10 Cheyenne trim. It is an automatic 5.7 350 with a 1406 Edelbrock carburetor. I just put a 1 inch phenolic spacer on it. Recently I had the local shop to do a complete tune up. New plugs, wires, installed new carburetor, oil change, brakes, installed flowmasters, and flushed the coolant. It’s been running really great!

About a week ago i noticed once it wouldn’t accelerate above 2000 rpms. It was very brief and went back to normal. Ran great for a few days and then it started happening more often. It has progressed to now where it will rarely go above 2000 rpms. I hoped it was bad fuel and ran some fuel additives, but it that hasn’t helped. When it does occasionally go past 2000 it won’t go past 3000. The truck sort of shakes and will not move past those marks. Moments later it might, but then it sends it righ back to to under 2000. It happens in drive, park, and neutral.

Anyone have any idea what I’m dealing with? Thanks guys.

 

[bucket]

Does the truck idle smooth? Is there a fuel filter installed?

 

[Cu1n81]

It idles great. Even in reverse or drive while stopped. It has a fuel filter near the carburetor. It was installed 3 weeks ago.it’s the clear kind. Seems unobstructed. Maybe a bad fuel filter?

 

[bucket]

I just realized you said it does it in park and neutral as well. That sounds like it's an ignition problem, possibly the pickup coil or ignition module.

 

[Cu1n81]

I just realized you said it does it in park and neutral as well. That sounds like it's an ignition problem, possibly the pickup coil or ignition module.

Okay so there may be something to this line of thinking. The truck had a MSD Ignition and blaster 2 coil. I replaced both bu the coil needed a different boot other than the standard 90 degree type. So I bought a kit and made my own. I’ve always wondered if that may be failing? I recently ordered one from MSD that’s made for the blaster 2. Could that be the issue?

 

[bucket]

What model of MSD ignition? Did you inadvertently set a programmable rev limiter?

 

[Cu1n81]

What model of MSD ignition? Did you inadvertently set a programmable rev limiter?

I got the MSD 6425 6al with a rev limiter. I’ve had it for a couple months and have been able to reach 4000+ rpms. Recently it’s started keeping me under 2000. Could the box be malfunctioning?

I do not believe this model is programmable.

 

[bucket]

I don't have any experience with those newer ones, but it says there's rev limiter knobs right on the box. Where do you have it mounted?

It just seems awfully strange that you are limited to 2000 rpm, no matter what kind of load the engine is seeing.

 

[Cu1n81]

I don't have any experience with those newer ones, but it says there's rev limiter knobs right on the box. Where do you have it mounted?

It just seems awfully strange that you are limited to 2000 rpm, no matter what kind of load the engine is seeing.

Adjusted the hidden knobs and boom it’s working properly!!! Thank you for pointing me in the right direction!!!

 

[bucket]

Adjusted the hidden knobs and boom it’s working properly!!! Thank you for pointing me in the right direction!!!

If they had never been adjusted before, I wonder why it let you rev past 2k previously? Where the knobs adjusted for a 2k rev limit before you just now changed them? Or did simply moving them fix it, like maybe one knob doesn't work properly?

 

[Cu1n81]

They were both set at zero before. Not sure what that means. Haven’t read enough on it. I definitely haven’t moved them previously.

 

[78C10BigTen]

Congrats @bucket ! Andy saves the day!!! @Cu1n81, good thing it was a silly simple fix!

 

[Raider L]

Ha, ha, ha, ha, this is great!