Starting Jota for first time for 20 years

S

Simon Yates

Senior member
The Jota fires for less than one second each time I try to start it, then stops.
Here is a picture of the Sachse ignition plate at TDC - can someone tell me if it looks correct please.
The arrow on the Sachse timing disc is reversed to that shown in the images (i.e. against the direction of rotation).  I am ignoring this and following the instructions which say rotate in DOR.
The sparks are good and I have tried swopping around the #1 and #10 coil leads.
It has new carbs so surely these are not the issue.
 

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looks to me as if the magnets are back to front
south turns the hall effect trigger on, north turns it off
way that is set up you have 300 degrees between events


 
If anyone can manage an image I would greatly appreciate it (at TDC if possible).

Further investigation suggests the following.
Curve zero fires happily.  All other curves work in the 0-400 rpm range and then cease to fire hen supposed to advance.  Seems to be verified by the strobe.

Maybe it is meant for mounting on the RHS as the arrows suggest?
 
Pull your plugs set your engine at TDC for number 1 cylinder turn that magnetic rotor over so the south magnet is following turn the ignition on earth the plugs and slowly turn the rotor until it switches the LED off (if you can still get to them) tighten the allen screws, and you should be right!
 
Looks to me like red is on the money. Seems you've got an incorrect rotor for your bike. The scribed arrow is a giveaway as well as the N & S markings. You could try flipping it over but then I dunno how you'd get at the grub screws to tighten it on the shaft.

That rotor will cause way too much dwell time, which will result in a saturated coil core. That will more than likely kill the spark within a few revolutions as residual charge in the coil builds up. If the engine manages to keep running, the coils will over-heat and die.

Get back to whoever you bought the ignition from and ask them to send you the correct rotor.

 
Dellortoman said:
That rotor will cause way too much dwell time, which will result in a saturated coil core. That will more than likely kill the spark within a few revolutions as residual charge in the coil builds up. If the engine manages to keep running, the coils will over-heat and die.
Get back to whoever you bought the ignition from and ask them to send you the correct rotor.
Click to expand...

I'd agree the rotor looks incorrect for the bike, but just as a comment, it won't cause too much dwell. The black box is just looking for a falling (or rising, depending on the box) edge on the trigger pulse for the timing reference. The hall switches do not actually turn on and off the coil as with points, all the smarts for advance and dwell are done by the black box.  The calculated ignition event is sent to the coil when it receives the timing trigger from the falling edge when the hall switch operates.

Given that in this case the duty cycle between high and low input is inverted (as Red alluded), the ECU is possibly losing the signal once engine fires as it is outside the range of expected inputs.
 
She is running :D.
Thank you Red and others for the knowledgable and informative postings.
The instructions on the Sachse ignition could have been more complete I must say. >:D
Regards
Simon
 
Simon Yates said:
She is running :D.
Thank you Red and others for the knowledgable and informative postings.
The instructions on the Sachse ignition could have been more complete I must say. >:D
Regards
Simon
Click to expand...

The rotor they show is different to yours, and correct direction.
 
I reset the height of the spacers under the Hall Effect trigger plate to suit the 'turned around' magnet plate.  Necessery due to spigot on one side.
It would have been helpful if the instructions contained a line such as 'Position the magnet plate so that, when viewed in the direction of engine rotation, the magnet marked S leads the magnet marked N by 60 degrees.

With the motor at TDC of course, rotated the ignition assembly one turn to set the LED's as described.
Then rotated the plate carefully until the North magnet just dimmed the LED and tighened it up.
Pressed the starter buttor and THANKFULLY the control box worked this time as the old bike started first time. :D :D :D

Thanks again for the help.
 
Now that it's running, it's a good idea to check it with a strobe, just to make sure it's not a couple of degrees off. It's bloody difficult to position the rotor spot-on using the LEDs. Sometimes it'll move as you tighten the grub screws. Might take a bit of trial and error to get it perfect.

Of course, if you have an Ignitech box, you can use the software (base advance) to correct for any minor error in the rotor position.
 
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