New ignition, new stumble
 

Symptom: On quick accel from rolling, the engine hesitates then surges. Not sure if "stumble" is the correct term?

What changed: I just picked up and installed a programmable timing distributor from Progression Ignition to test out (was interested in adding vacuum advance). Was previously using a MSD 6AL box w/ MSD Blaster 2 coil and MSD distributor for magnetic pickup (no ballast resistor).

I'm currently bypassing the 6AL box entirely, and have the new distributor wired up to the existing coil. PI says the Blaster 2 should work great.

My limited understanding of timing doesn't seem like this is a symptom resulting from improper settings.

I'm wondering if it's a side effect of switching from capacitive discharge (CDI) to inductive spark? I forget what I gapped the plugs to, but haven't made any changes so maybe that needs adjustment now?

Prior to swapping out I was adjusting the carb and have things pretty lean, but was working well with the MSD distributor/box.

Suggestions?

After just watching a 700 hp Nascar engine on their videos, I doubt your new ignition is an issue.

Impressive system.

Can we see some screenshots of your ignition timing table?

Programmable timing is susceptible to rotor phasing issues which can cause crossfiring, stumble, flameout etc.

I'm wondering whether this been addressed in their design.

Gary

I'll try posting some pics tomorrow. But yeah, I don't think that's the issue. One thing I did try was to create a table with vacuum advance set to zero to remove that variable. I've been mostly testing 18* to 36* range "curves" maxing out at 3k rpm.

The distributor comes with a fixed 10* BTDC advance, and they have you set it all up and verify with timing light before creating any custom tables. I'm not sure if that would address rotor phase or not. I'm not sure how I would adjust that without destroying a dist cap to view the spark.

With an MSD programmable such as a 6530, you would check rotor phasing by drilling a large hole in an old cap, and use an adjustable rotor.
I would assume your new distributor takes this mostly into account, since the manufacturer has set the minimum at 10BTDC.

Sounds like you are on the right track.

Looking forward to your screen shots.

Gary

+1^ on what Gary is saying. If the rotor phasing is off and your advance table gets the rotor far enough away from the intended cap terminal, the spark can intermittently decide it is easier to jump to a different terminal. The moment that occurs the correct cylinder doesn't misfire is just doesn't fire at all. The effect is a nosing over of the engine torque curve that you feel as the phenomena you have reported experiencing.

You will use up one cap to correct the phasing but it is worth the price of a cap. The other thing you need is an adjustable rotor to allow correctly repositioning the tip of the rotor. I am not sure if their rotor is custom to their ignition system or if it is generic and possibly has an adjustable cousin available that you can buy. In a worst case scenario you can always modify your rotor to make it adjustable but it is much easier to just buy one if they are available.

It is worth a call to PI to see if they offer one or can point you to one. It is also possible they have built into their unit an adjustment to accomplish the same thing by another method. Definitely give them a call and listen to what they have to say.

BTW that is a waaaaay cool distributor. It gives ignition map control capabilities just like ECU controlled coil on plug systems — very nice! And I love the smart phone control system.


Ed

When I first started tuning my engine, I had a stumble when accelerating from low rpms. No amount of carb tuning (mostly accelerator pump cams) would change it.

I finally started bumping up idle timing (while keeping the max timing of 38 constant) and the hesitation/stumble finally went away.

Mine wasn't over-complicated to sort out as I don't run vacuum advance.

Hook up a timing light and slowly rev the engine. Watch the advance of timing. Should start advancing immediately and be all in by around 2000 rpm.
I have a hunch your timing Advance isn’t coming in fast enough for these light cars.
A lean carb at tip in will also exhibit the same characteristics.

Make sure you aren't losing timing as your rpms go up. Those with manifold vacuum advance running at idle /cruise then accelerate will lose their vacuum advance and the motor will stumble until it can catch again.

Here's the chart I tested just now.
http://www.clubcobra.com/photopost/d...n_Ignition.png

I had been using an all-in of 3000 rpm which was the default. Given jhv48's comment, I tried lowering that to 2000 rpm. Still with vacuum advance set to zero to remove that variable. Still seeing the same behavior. The app provides realtime feedback, so I was able to cruise at about 2500 rpm and see the advance clamped to 36, but still get the hesitation and surge on quick accel.

On the way back I noticed the amp meter needle bobbing toward 60 with acceleration. I don't remember it being so sensitive to rpm changes previously, so I'm wondering if that has any bearing.

That should not happen. Something is not right.:cool:

This sounds like your problem.

re: rotor phasing (from Progression Ignition)
I need to track down the amp draw still. PI suggested maybe there is a resistor wire somewhere still. I don't think that's the case since the engine was set up with an MSD ignition box already. On ERA the ballast resistor should be mounted on the driver side engine bay aluminum tire cowling, and I've never seen one.

If there is a 60A spike negative, then there is a partial short to ground on something, which could be a fire risk.

Good to hear the Progression Ignition company has addressed the design for phasing.

Any progress on this issue?

Haven't had a chance to work on it. I think I sorted the ammeter out (mostly) by replacing the battery. It's still a bit wobbly. May wind up replacing that too just to be sure, but haven't ordered anything yet.

The distributor works great. My tach reads a little low - not sure if that's new behavior or not since I never checked it that closely before. I've been meaning to research if there is an adjustment for that or not.

My next plan of action is to re-examine the carb unless anyone has other suggestions.

ignition box
 

Just wondering since I already have a msd box could I use it with the distributor or should I . I will admit I do not know much how these things work.:confused:

If your engine runs well without the MSD box, I suggest you leave it alone. I've run MSD boxes and they fail more often than I'd like. I don't have one now.

I am running a MSD 6AL-2 Programable and love it. The flexibility of the programming is really cool.

As others said, I don't think your issue is timing.

John

For whatever it's worth, guys I know that run
MSD digital 6AL boxes who experienced failure
connected a MSD 8830 Noise Filter Capacitor
into the 12V BEFORE going into the CDI box.
8830 cleans up the power and provides spike
protection. None have failed since.

Link:

https://www.summitracing.com/parts/m...yABEgJWifD_BwE

I had 2 6AL failures