1971 750 commando tuning

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rob carter

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how do you tune a 1971 750 commando with a Mikini 34mm carb and a Warsell electronic ignition?
I have no strob and was wondering how to set the timing to 28degrees, or is this not required ?


Rob
 
Use a degree wheel and a tdc indicator. If you still have points ignition, everything depends upon your ability to break the points and make a spark at exactly the correct degree setting...TWICE, once for each point set. With EFI, you only have to do it once. IIRC, thee's also a timing plug in the crankcase that can be removed and the crank stopped at 28 degrees btdc.
 
rob carter said:
I have no strobe and was wondering how to set the timing to 28degrees, or is this not required ?
Click to expand...

Decent xenon strobes are not very expensive.

Some will recommend you just set the ignition by advancing it until the engine pinks/pings under load then retard until it stops pinking, but I suggest you set it with a strobe if you can.
 
I have checked the bike out and there are no points.Only electronics
I notice the degree setting wheel.What tool do i require to change the setting and how do i do it.I understand that the piston requires to be at top dead centre for the spark to ignite the fuel.

Rob
 
rob carter said:
I have checked the bike out and there are no points.Only electronics

I notice the degree setting wheel.
Click to expand...

Could you explain? Do you mean the timing scale in the primary cover? A 'degree wheel' can be fitted and used to check the accuracy of the timing scale.

rob carter said:
What tool do i require to change the setting and how do i do it.
Click to expand...

As it has (Wassell) electronic ignition then what you need is a strobe.


rob carter said:
I understand that the piston requires to be at top dead centre for the spark to ignite the fuel.
Click to expand...

When set correctly, for starting and slow running the spark should occur slightly ahead of TDC and will advance further from TDC as the revs increase until it reaches maximum advance which should be 28/31 degrees BTDC at 4,000-5,000 RPM for Wassell EI and why a strobe is required as there is no other way to check this.
 
Thanks for that
What adjustment am i required to do to achieve 28/31 degrees and with what tool

Rob
 
rob carter said:
What adjustment am i required to do to achieve 28/31 degrees and with what tool
Click to expand...

If a strobe check shows it needs adjustment, then small spanner/wrench to loosen the two pillar bolts that hold the Wassell 'stator plate' should be all that's required.

The position of the stator plate is altered to set the correct ignition timing.

http://www.grintriumph.com/images/Elect ... W61495.pdf

22
Start the engine and warm it up to normal working temperature for 4-5 minutes. Connect a
strobe lamp and time with the engine running at 4000-5000 RPM. This is adjusted by sliding
the stator plate on its slotted holes. If timing marks cannot be aligned before the end of the
adjustment slots then the magnetic rotor must be re-positioned
Click to expand...
 
rob carter said:
I have checked the bike out and there are no points.Only electronics
I notice the degree setting wheel.What tool do i require to change the setting and how do i do it.I understand that the piston requires to be at top dead centre for the spark to ignite the fuel.

Rob
Click to expand...

Not exactly at TDC for spark. It occurs at 28 degrees before TDC at maximum advance and on a curve based on engine speed up to that point. Generally set advance at 28 degree BTDC at above 3000 rpm engine speed. If the bike is running now and you just want to ball park the ignition setting, run at idle, loosen the two pillar screws a bit on the ignition timing plate and turn very little counter clockwise until the idle begins to stumble. Then rotate back just a bit to get a smooth idle. Warning if too far advanced the bike will let you know when kick starting...it will kick you back harder. :(
 
Its all clear to me now.
I will buy a strobe and do it that way,with the only adjustment being the wassell rotor, cheers !! I will let you guys know how it goes.Incidently I cleaned out the Mikuni carb and it now looks good, the float looked like it was stuck and was over flowing when I turned the petrol on.


Rob
 
rob carter said:
with the only adjustment being the wassell rotor,
Click to expand...

Hopefully, you meant the Wassell 'stator' as it's only necessary to adjust the Wassell 'rotor' position if the correct ignition timing can't be achieved within the range of adjustment allowed by the stator slots.
 
I notice that one of the posts mentions the advance should be 28/31 degrees BTDC. I suggest you should always set your timing to the same maximum advance figure and tune your carburation to get the optimum performance to suit your application. With petrol, I would use 28 degrees max. advance unless the petrol company says different. If the ignition timing alters, it can give the same symptoms as changing jetting. (The two are inter-related and the result of changing either is variation in combustion temperatures ) - Timing first, carburation second.
 
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