DYNA S Static Timing for Idle or RPM < 1,500

[MisterCinders]

Yes, I did a search.

Hunting down a very strange idle issue has me wondering about the ignition timing. The idle issue is detailed here

Basically, the idle likes to drop from 1,200 RPM into a steady and choppy low 900 RPM that does not respond to the idle screw. Plugs are tan, and the idle doesn't "sag" and return like a rich pilot symptom. I have new coils, a Dyna S, fresh plugs and wires, etc. This keeps happening with fresh wires, coils and plugs, so I wonder if the forward timing on the bike is off. In other words, if the idle works at 1,500+ but slightly struggles below that, perhaps the timing falls apart at the very bottom end of the range.

Another clue in this puzzle is the Dyna timing method and my terrible skills. Dyna says to static time the ignition against the advance marks, which are the right-hand F marks.

I did this when I installed the ignition, and it is a very fiddly process. The instructions literally say to hold the rotor clockwise and then turn the engine (also clockwise) until the light comes on. Even with three hands to hold the wrench, timing light and the advancer rotor, getting a wrench on the engine to turn it while keeping the advancer in that position against the spring tension is a severe PITA. IIRC, I ended up having to get it close with the engine and then turn the rotor to sneak up on the timing mark. So I am suspicious of those timing results.

I have tried just going with the points timing process, where you leave the advancer alone, and reference the left-hand marks. For whatever reason, that didn't work well with the Dyna, and the light never came on IIRC. I have been able to somewhat confirm/set non-advanced ignition timing with a grounded plug, but that is pretty fiddly too and requires keeping an eye on the timing marks and the spark. Sometimes you can hear the spark fire, though.

So does anyone have ideas on how else to drill down into the low RMP timing?

Are there any tricks for keeping the advancer rotated to better time the ignition per the Dyna instructions?

TIA

[OldVet66]

You are having fits with that bike. Is the mechanical advance possibly binding? That's about the only thing that I can think of that could cause erratic behavior with a Dyna-S. Initially mine was statically timed to get it running. Later after getting some miles on it I used a timing light and found the 2-3 module needed to be tweaked slightly to get it dead on. It's easier to check to see if the advance is working properly with a timing light also.

[mike_of_bbg]

Personally I never did the static timing and would suggest that you beg, borrow, buy or steal (OK, don't steal) an inductive timing light.

But yes, is the mechanical advance free to move? I've always been surprised by Dyna's inclusion of what appears to be a too-thick spacer for use on the factory EI bikes, which will lock down the mechanical advance when tightened so it cannot, ummm, advance. I sanded down my Dyna rotor top to make adequate clearance for advancing. It occurred to me later, with the static timing procedure, that maybe Dyna wants the MA locked down. Though, for the life of me I can't see why...

That your idle screw is not actually adjusting the idle is odd. How long since you've done a proper vacuum sync? I wonder if one of your butterflies is too closed - that can cause the others to hang open, and can also cause that cylinder to drop out at idle. EDIT - Never mind, you have VM carbs so I don't know what I'm talking about; you don't even have butterflies...

[OldVet66]

Just a guess, that washer might be fine when you start the bike, and it binds when it is hot and expands a bit, sticking the mechanical advance all the way advanced so it doesn't want to idle. I would remove the washer and sand it anyway just to be sure. Mark the timing plate on the plate and case so you can just tighten it back up on the marks and it will start. Do check it later with a timing light.

[Nessism]

When installing the Dyna S on my old 550, the timing was set to the F mark, not the full advance mark while holding the rotor like Dyna suggests. The advance is what the advance is, but you have control over the idle timing.

[salty_monk]

I've found it doesn't matter which mark you time it to.... It should be the same thing anyway.

Try it and see. 1000-1100 is a more realistic rpm idle number in my experience, also try an electronic tach (my timing light has one built in) to make sure that your tach is actually reading accurately (if your 900 is actually 800 for example it definitely won't run).

[MisterCinders]

Reset the timing on the forward mark. Used the basic method for points. Bike ran fine, but the idle wierdness stayed. So I rebuilt the carbs. Again.

Running better so far. Mystery unsolved.