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fernsteve
15.08.2018, 06:49 PM
I posted earlier that I fitted this ignition on to 750GT and got the bike running - it started no bother but was only running on the horizontal cylinder. I had another bike to work on (and get sold) so put it to one side. I figured a loose wire, duff coil/plug or something and would fix later.

I just got back to it now and I have refitted the Sachse from scratch making sure I fitted everything by the book - even fitted new coils I had, plugs, leads etc - but it is the same thing. Only firing on the horizontal cylinder.

Is there a mistake in the instructions, should it be timed on vertical cylinder rather than horizontal?

Steve

Derek
15.08.2018, 08:50 PM
I have no knowledge of the Sachse ignition but on the bevels TDC on the vertical cylinder is the timing position.

81mhr900ss
01.07.2019, 10:47 PM
Way late joining in on this but just in case someone else comes looking for Sachse advice, I installed my Sachse system on an 81 MHR about a month ago so have some observations/comments to share.

Before doing the full installation, it's possible to test the spark delivery equipment; the Sachse unit has a small dial on it. When set to the "0" position and powered, grounded and connected to the two coils, and with the plugs removed but connected to the caps and grounded to the motor, there should be continuous sparking on both plugs; this tests the coils, HT leads and plugs. It's a good idea to do this first in case there's an issue with the new Sachse unit.

The firing sequence on the bevel twins starts with the front "orizontale" or "O" cylinder followed by the rear, "verticale" or "V" cylinder. I use "V" and "O" because this is original Ducati nomenclature. What Derek is referring to is the cam timing set-up; making all the bevel gear dots align when putting the motor back together and as he notes, the rear, vertical cylinder is set at TDC with all the dots aligned.

The Sachse system is very simple and uses the front cylinder to set-up the new trigger wheel timing. The manual states to estimate very close to TDC on the front cylinder (does not matter if it's the compression stroke or exhaust stroke TDC as the Sachse system is a "wasted spark" system and fires on both) and to adjust the trigger wheel so that it's timing mark is pointing towards the vertical head. On my 81 MHR, this is really easy as the crank key slot points to TDC on the front head. You are then supposed to put the clutch casing on and turn the crank slowly while looking at temporary trigger LEDs, estimate how early the red LED is going off (it's to go off at TDC) and then take the casing off, tweak the trigger wheel a little and try again. This made no sense to me; I took a few extra seconds at best estimating TDC and trigger wheel direction and when the casing was back on the red LED shut off exactly at front TDC and the green LED exactly at rear TDC 90 degrees later. Good enough for me; remove the casing, Locitite the three little grub/lock screws on the trigger wheel and put the casing back on.

I added a new Shendingen regulator to protect the expensive Sachse box and used new, 5ohm DynaTek coils and HT leads and new NGK caps. As recommended in the Sachse manual, I used both of the units ground points. From what I have read, the Sachse systems are prone to failure when grounds are bad and feed voltage is spiky. If using old equipment that has tested OK, I still recommend removing the plug caps, cutting off the last 5mm of old HT lead and reattaching the caps. I use a little dielectric grease on all the rubber parts.

I can very easily kick my bike over from cold while striding the bike; about 6 seconds of tickling, one accelerator pump squirt and one good kick.

81mhr900ss
01.07.2019, 10:58 PM
Again, way late, but to specifically address fernsteve's problem (I hope it's fixed by now) I would first run the Sacshe unit test mode as described above. If only the front plug was sparking then I'd swap the Sachse coil outputs and run the test mode again to see what happens. If now the rear plug is sparking then there's an issue with the Sachse unit; the vertical cylinder output is dead. If the rear plug is still not working then there's an issue with the rear coil/HT lead/plug cap/plug.

The Sachse unit is connected to wiring using tiny clamp screws. Equally tiny ferrules are provided to be crimped onto the ends of the wires. These have to be pushed all the way into the holes on the unit for the little clamp screws to hold them down.