750SF ignition adjustment

oehlin

oehlin

Junior member
Location
Sweden
Has now mounted the ignition plate and adjusted the points according to the manual.
The problem is that I have to set the rear points to the left cylinder and the front points to the right cylinder to make it all work and not the other way around what the manual says.
Would think the points cam has been mounted 180 degrees incorrectly.
The A-mark is checked against TDC .
Is this setup OK or do I need to fix it.
The engine a 750SF 1973 has been disassembled and assembled by a probably experienced Laverda mechanic
 
it doesn't really matter which set of points fires which plug, as long as the base plate " fixed set" are bang on correct timing, and then as a secondary vital check, the "moving set" is also then bang on.

If it bothers you, very easy to swap around.
CLEM
 
CLEMTOG said:
it doesn't really matter which set of points fires which plug, as long as the base plate " fixed set" are bang on correct timing, and then as a secondary vital check, the "moving set" is also then bang on.

If it bothers you, very easy to swap around.
CLEM
Click to expand...
They are. Thanks
 
oehlin said:
Has now mounted the ignition plate and adjusted the points according to the manual.
The problem is that I have to set the rear points to the left cylinder and the front points to the right cylinder to make it all work and not the other way around what the manual says.
Would think the points cam has been mounted 180 degrees incorrectly.
The A-mark is checked against TDC .
Is this setup OK or do I need to fix it.
The engine a 750SF 1973 has been disassembled and assembled by a probably experienced Laverda mechanic
Click to expand...
A: as Clem says, it doesn't matter which is which, if the bike doesn't fire, swap plug leads or wiring to the points. Points cam is set by a woodruf key on the drive shaft. Cannot be wrong. Normally.
B: however, as in English, A is for Advance, 32 or 36° before TDC, certainly not TDC which is PM, punto morte.
C: you're quite right saying "probably" experienced Laverda mechanic.

Paul
 
Paul Marx said:
A: as Clem says, it doesn't matter which is which, if the bike doesn't fire, swap plug leads or wiring to the points. Points cam is set by a woodruf key on the drive shaft. Cannot be wrong. Normally.
B: however, as in English, A is for Advance, 32 or 36° before TDC, certainly not TDC which is PM, punto morte.
C: you're quite right saying "probably" experienced Laverda mechanic.

Paul
Click to expand...
Then something i wrong ?
When the piston is i topp and the rocker arms are lose. The A mark is allgne with the mark on the engine case.
Then I set the points to open on the P/M mark
 
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oehlin said:
Then something i wrong ?
When the piston is i topp and the rocker arms are lose. The A mark is allgne with the mark on the engine case.
Then I set the points to open on the P/M mark
Click to expand...
Forget the rocker arms. Piston at TDC = PM. First one side, then 360°, the other side. Set points to open at PM mark. First one side, 360°, then the other side. Then, if you want to check the auto advance unit, use a stroboscope, 3000 rpm and A should align with the mark on the case. A is for advance only, nothing else.

Paul
 
With one plug out, but still connected in the socket and earthed against the
housing, if you turn the engine over very slowly, you can see when it sparks.
If it is the one leading to the side where the rocker arms are released you're
in the right path.
If not swap either the ignition cables or the wires connected to the points.

Ernesto
 
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The "A" mark is at 40 degrees BTDC on all the twins I have seen. If you set a wire pointer to the PM mark when either piston is at top dead centre, and are able to get the timing to open at that point with the points set to the correct gap, your timing will be correct. If you can get one set of points to be correct and the other is impossible then the auto advance shaft may be bent or not correctly seated.
If the mark on the crankcase does not align with the PM mark on the starter clutch pulley at TDC you most likely have a missing or broken key in the starter clutch pulley. If you are unable to get the points to open at TDC with the correct gap set, the oil pump/ignition drive gear is set up incorrectly to the crankshaft gear and you will have to remove the LH cover to rectify it.
 
Dellortoman said:
I don't know much about the 750 twins, but don't they have non-wasted spark ignition? (fires each plug at 720° intervals). If so, then you need to check the rockers to see what stroke it's on.
Click to expand...
Yes, if cam timing and points cam are properly set. If that's the case and it's not firing, swap plug leads.
No need to be more complicated.

Paul
 
Paul Marx said:
Forget the rocker arms. Piston at TDC = PM. First one side, then 360°, the other side. Set points to open at PM mark. First one side, 360°, then the other side. Then, if you want to check the auto advance unit, use a stroboscope, 3000 rpm and A should align with the mark on the case. A is for advance only, nothing else.

Paul
Click to expand...
Should the point gap 0,4mm be set att the point cams highest spot ?
 
"Piston at TDC = PM. First one side, then 360°, the other side"

not quite accurate Paul, when the PM mark is aligned with the very small nick in the inner cover (crankcase) BOTH pistons are at TDC.
One is on the firing stroke the other at exhaust stroke, but for sure they are both at TDC
CLEM
(TDC = top dead centre)
 
free input no one asked for, firstly the points gap is to establish "dwell" duration, to properly saturate the ignition coil primary winding and core steel laminations. It can set without concern for the actual gap dimension, 50% error and the gap will still work, provided the initial opening of the points is set to the desired ignition point, cold crank and idle, usually 5dBTDC. Too wide a gap, mostly no effect, too small a gap and there may be a tendency to cook the coil(s) resulting in feeble/erratic spark, maybe. Once sorted a Guzzi MK something on the side of a road, old transistor radio near the coils, set timing marks on the case/flywheel, jog the back wheel, transistor radio went "tick" when the points opened, lady owner reported it never ran better, did not bother with points gap setting at all.

Thought PM was Punto Maximo from my factory manuals here...as if i knew, tourist italian at best for me... also the timing mechanical marks are indicators not precision engravings, why i used to include a piston dead stop in the iis kit, to set or confirm the exact TDC on each motor. Some factory "marks" were out by 5 degrees or more. Fabricate one from a discarded spark plug, suitable for Laverda heads. Regards to all.... j.
 
CLEMTOG said:
it doesn't really matter which set of points fires which plug, as long as the base plate " fixed set" are bang on correct timing, and then as a secondary vital check, the "moving set" is also then bang on.

If it bothers you, very easy to swap around.
CLEM
Click to expand...
Hi this is such a great thread. When doing a static time on my twin the base points can be set fine but the "moving set" run out of adjustment before i can get them right. Any ideas please?
 
Are the ignition points new? If used what condition are the plastic parts of the points that rub on the cam? If worn you can run out of adjustment. Also it is common for the advance mechanism to be worn out from lack of maintenance. It should be periodically cleaned and lubed which no one ever does until it no longer works.
 
Also, or trim the less than usual "dwell" to allow the lost adjustment to be reclaimed.

1200ts is very correct as to age related maintenance or rectification work, practical advise at it's very best. j
 
1200ts said:
Are the ignition points new? If used what condition are the plastic parts of the points that rub on the cam? If worn you can run out of adjustment. Also it is common for the advance mechanism to be worn out from lack of maintenance. It should be periodically cleaned and lubed which no one ever does until it no longer works.
Click to expand...
IMG_20220104_174524.jpg
I thought the blocks were ok but a crap macro photo shows maybe not so good
 
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