dizzy springs

[baltobernie]

Here is a photo of my distributor plate:



During my engine rebuild process, I had this stock, single-point Marelli unit recurved by a guy who supposedly knows what he's doing. He asked all manner of questions about compression, cams, carbs, etc. He did not enclose an advance curve with the rebuilt unit.

I'm still chasing a stumble under load with light throttle, almost always around 2500-2700 RPM. I've gone rich to the point of blackening the plugs and loading up at idle (11:1) in order to eliminate this stumble.

I'm now wondering if the problem may be ignition-related. Maybe he cranked in the advance too soon? I'm seeing 36° total, so I know I'm not overboard with either initial or centrifugal. From what I've read, there are usually two different springs on the centrifugal mechanism, an early "weak" one and a later "strong" one. The story seems to be that the weak spring is to quickly advance the timing under low RPM, the the stronger one kicks in (around 2500 RPM) to flatten out the curve. Otherwise, they say, it wouldn't be a curve at all; rather a straight line.

So ....

1. Which of these in the photo is Low?
2. Is it possible he put in two Low springs to amp up advance, and that's what causing my stumble? I have a couple of salvage Marelli springs I can try, if an expert can show me the way.

[124JOE]

the one one the left is the low spring

[baltobernie]

Thanks, Joe.

I gotta ask - How can you tell 'em apart I have some larger-diameter ones - I think I'll try one in the Hi side.

[124JOE]

the one on the right has 15 coils so it kicks in later
the left one has 12 coils and is under load

im using the curve kit for a chevy it has three sets we use the smallest,it gives the quickest pedal
and it gives a straight line.i just live with the boble in the idle.

[131]

The one on the left has 12 coils and is already under tension, it will hold the weight in until higher revs. The one on the right with 15 coils is not under tension, the weight will move sooner under lower revs and reach full movement with less spring tension.

[baltobernie]

Thanks, guys. I installed a stifer spring on the right side ...



... so that should slow the rate of advance on the top half of the rev range. I'll give it a try as soon as it stops frikkin' snowing!

[131]

That means the spring that was previously your second weight to advance will now be the first and the other will come in later. This will delay your total advance until a lot higher in the rev range.

[124JOE]

as i see it.you had a curve above the 45 degree straight line
now your curve is below and you will see a differance.its all in the pick up and go part

[baltobernie]

I swapped out my recurved dizzy for a stock Marelli Plex system, just for giggles. No change. I put the recurved Pertronix back in, then reduced the static timing to 7-8 degrees, and the stumble has diminished greatly. Who woulda thought a degree or two would make such a difference. I guess I was just over the edge at 10. Also checked spark with a cheapie gap gauge; 14mm, which is plenty strong enough (Bosch blue coil).

Now it's back to idle jetting and beyond. I think I'm getting close Let's see if I can git 'er done before decommissioning for Winter.