Friday a friend of mine brought his '74 '73 teener with D-Jet over to get some help installing the 123 dizzy with bluetooth. Until I went Microsquirt I ran the older (non-bluetooth) version on my 2056, also with '74 D-Jet (using curve "B").

Anyway, got the dizzy in and the car started pretty quickly. Everything went smooth until I mixed up cylinders 1 and 2 and had it all whacked for a while (honestly, I think I'm at the point in my life where learning something new means forgetting something I used to know like the back of my hand....like where cylinder 1 is on the type 4. In fairness to me, I didn't wrench on my teener all last year while I was working on my boat, but still...I hereby turn in my official teener card in shame ).

Anyway, got that sorted after a bit and then we tried to make sure we timed the dizzy so it matched the phone app. Shot the timing light for 27 with the curve at 27, so in theory we were calibrated dizzy to app. Then we put in the basic curve so he could drive home. Car pulls strong and feels good with two exceptions:

1. There's a slight hiccup (as he describes it) between 2200 to 2800 RPM. He's not saying a "flat spot," but rather more like something intermittent that I would associate with a loose plug wire or injector ground. Curious, though, that it does it consistently at that RPM range. Can a misadjusted curve do something like that?

2. Car is idling around 1600 now with the idle bypass fully closed and even with total advance (static and crankshaft) at 0 for 500 and 1000 rpm. Tried plugging up the vacuum advance line and hooking up the vacuum retard, but that had no effect. On my old 123 dizzy I used curve "B" with retard, and that's what got my idle to behave. Assuming we don't have a vacuum leak somewhere, and assuming we correctly timed/calibrated the dizzy, how else do we get idle to cooperate? I see the MAP curve has some potential to do this, but it's kind of confusing on 123's website, and I am kind of surprised that I don't see anyone else here, AFAIK, using the MAP curve.

We're probably doing something basic incorrectly on the centrifugal advance curve, but it's not clear to me what that is. Still learning the app...

I have the old school 123 but imagine the popcorn emoji here.

Mark the zero mark and verify that zero is actually zero. Are you sure the 27 deg mark you timed it off of is correct? 1600rpm idle you either have an air leak or a good deal to much advance. If you are sure the timing is what it says it is I would check the aux air valve and the crank case breather valve (Technically I would check everything but those are the first 2 places I look) Zero advance should be plenty low enough for idle, these things tend to be happiest around 8-12 usually but djet doesn't always play nice with that much. Ultimately running negative advance on the vacuum map is what you will want to do in order to get the quickest off idle response. Running zero degrees at idle centrifugal only is going to make the throttle response real sluggish at low RPM. Best performance is probably going to be setting idle advance on the centrifugal map somewhere in the mid teens and then use the vacuum map to add 5-10 degrees negative advance to bring the idle down. That way as soon as you step on the gas from idle advance immediately jumps up that 5-10 degrees giving you immediate torque without having to wait for RPM to build.

thats for after you find your intake leak though

Your problem with the stumble could be related as well. d-jet is "fun" especially at lower RPM in that changing timing changes the engine vacuum profile and having the wrong vacuum for a given load means you wind up with the wrong mixture at that RPM/load. Unless you plan on tweaking the MPS d-jet tends to be happiest with everything set as close to spec as possible.

Hey James -- I think you could be right. There is a greater than 0% chance that this is the issue. When he brought the car over last year for some tuning I noticed he didn't have a timing mark on the fan, so we did our best to mark one. I thought we had TDC, but we didn't pull the valve cover to verify, and his engine tin rubber is so well sealed I can't get a view of the flywheel mark at the back. Tried to verify from underneath the car, but I can't remember if we added that mark to the flywheel at the same time.

Next step is to verify this 100% I think.

You have an intake leak somewhere that was likely masked before. Or an old hose fitting got nudged and cracked. 1600 rpm hot idle is not a big leak, but that is more then just advance could cause - especially with the idle screw in all the way.

Smoke machine makes it really easy to find too. I have a thread on that somewhere of the one I built.

Zach