DMC2 - 750 SF0 - Arse about Face???

Haggis

Haggis

Hero member
Location
UK
Hi Witt fans.

I'm fitting a DMC2 to an SF0 and have  brain zone-out on setting the rough timing.

Instructions say.
1) Motor at TDC
2) Get it sparking - i.e. photocell seeing through gap.
3) Turn photocell clockwise until sparks just stop.
4) You have a rough static timing - do you dynamic checks from here.

I can't get that. My open and shut situations seem to be different to Uwe's. When I set the general arrangement is as per the sketches in the instructions. ?

My scenario 1
1) Motor at TDC
2) Get it sparking - i.e. photocell seeing through gap.
3) Turn photocell counter clockwise until sparks just stop.

My scenario 2
1) Motor at 40?BTDC
2) Get it sparking - i.e. photocell seeing through gap.
3) Turn photocell clockwise until sparks just stop.

Both scenarios have a very similar baseplate setting, so no clues there.

When I try to achieve Uwe's instructions, the 3 x fixing slots do not  line up.

I am taking 'photocell clockwise' as being viewed from the LH side of the bike. If Uwe means from the RH side, then that would explain it.

Thoughts? Tips? Where did I goof?

Cheers

Paul
 
Paul

DMC/2

Make sure plugs are removed, plugged in and grounded to engine, and ignition is off.

Engine at TDC

switch ignition code to 0 position - very important!
Turn base plate clockwise as far as it will go
turn ignition on
Slowly turn other way until spark at plugs
Check uninterrupted spark at both plugs
Turn again clockwise until spark stops.
Photocell should be screwed on exactly where the transition point from continuous igniting to non-igniting occurs.

Turn ignition off, replace plugs into engine & switch to positon 1 on box, and check timing with a strobe light.

Good luck,

Joe
 
Paul,

I don't bother with the "static" timing set-up.  Simply bolt on the base plate with the screws mid-slot, close enough to get the sucker running (this does however mean the timing/oil pump gear must be correctly orientated to the crank gear, and a healthy battery helps too!).  Dynamic check  with box set at curve #1, for 40? at 4000rpm, adjust as required, finito.  You can then play around with different curves if so inclined.

I use the #0 setting only for checking basic functions of the box and to check that the plugs spark correctly.

piet
 
Hi Paul

Are the instructions you're reading 750 specific?  The base plate is of course 'wrong way round' compared to triple installations.
 
Thanks All,

I've given it a good dose of thinking about and have concluded that something is wrong with the bike (and not my interpretation of the instuctions). But it's bloody confusing.

I decided the oil/ignition>crank gears must be incorrectly aligned. Although I found it is close to the right place as the keyway to the ignition advance carrier is just after the 12 o'clock position at TDC...
40837747605_8cca8b8294_c.jpg

Maybe 1 tooth to far advanced?
 
Yep, none of which are mine - all being ignored :-)

I'm taking it all back to basics - many compromises and bodges on this bike.
 
Thanks for the link Rob, it made me laugh as I've just been painfully counting teeth on old pictures of oil pump drive gears! I counted 44 and your post instantly confirmed it. :-)

44 teeth = 8.2? each = 16,4? at the crank, so 2 teeth would allow me to have the DMC-zero setting spark break at TCD and have the mounting slots in the correct position.

The link helped my near-conclusion - rip the primary off and check it all for mechanical integrity, then ignore what assembly angles I find and just put the drive gear where it is needed.

What did my head in, and got me over-analysing, was it all setup perfectly at 40?BTDC, but not at TDC. Kinda threw me - was I misreading the instructions or was the bike on the twist?
 
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