I have noticed my new 383 engine has a very slight fluctuation of RPM at times. Maybe 50 RPM or just enough to notice. I have a new MSD system and wonder if the MSD 6A could be causing the fluctuation. Also, I have a new Holley 750 with electric choke that someone told could cause the rpm to fluctuate slightly when driving. The engine dosen't do it all the time.

Are you seeing a tach movent or engine sound difference?
Is it a facory tach?
Are you using the MSD tach output terminal to the tach?
Is it at ildle or driving on the road?
What distributor?

David'
I notice it at idle and on the road. I am running all MSD 6A, Blaster II, and MSD Distributor. I notice it in the tach and I can feel it on the road sometimes. My tach isn't stock and is hooked up to MSD outlet. On the hiway I can feel it sometimes. Not real noticable but still I can feel a slight rpm surge.

try opening up your idle adjustment screws 1/8 turn.
yeah,i know it ain't supposed to work,but try it!
Eric B

You haven't mentioned when the fluctuation occurs in the RPM band. It could be valve spring harmonics.


Larger Dave

I notice the surge sometimes at idle(900rpm) and at cruze speed (2600 rpm). It dosen't do it during acceleration. Could fuel/air mixture be to lean, or possible vacum leak??? It started after about 50 miles on new engine and is only slightly noticable.

It might be your distributor advance weights. You might try changing one spring up or down and see if the fluctuation goes away or changes.

It could be the carb is a bit lean at those points. check your float levels, check for vaccum leaks.

Is the Msd coil made in Mexico or does it have the chrome sticker at bottom of can that say made in USA. There was a run of bad coils that were made in Mexico. Also found comments on this site about this.

I bet its just a little lean on the primary

You are right. I adjusted the fuel/air and seems ok now. I think my timing is still a bit off and will start playing around with it. I probably should dyno the engine to be certain. I live about 7 miles from Famoso Drag strip and the weather here today is perfect for the March Meets. Yesterday was wet off and on but they managed a few runs. Also, some real nice Camaro's were on hand both on the strip and at the "show and shine".