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Commando Ignition Timing Puzzle

Submitted by richard_potter on Sat, 15/10/2022
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Commando

I checked the ignition timing on my Pazon SureFire equipped ‘72 Commando only to discover that the previous owner had set the ignition timing to be circa 40 degrees maximum advanced.  Bike seemed to run and start ok; exhaust headers were a golden colour. Thinking that the previous owner had made a mistake I adjusted the timing to the (Pazon) recommended max of 31 degrees.  Bike started ok from cold but, after warming up, the header pipes have a mottled blue discolouration and the bike is reluctant to restart when hot.

Can anyone throw any light on what might be going on please?  I’ve check the timing marks on the primary chain case with a dial gauge and a timing disk; the marks look to be accurate so it truly was running with 40 degrees max advance previously.

Regards to all

Rick

Submitted by john_holmes on Sat, 15/10/2022

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Is this a static timing or strobe timing, with analogue EI the electrical components inside the box  have tolerances which combine to vary the timing. The static timing is only so you can get the bike started, then you strobe to get it accurate. I have had boyer boxes vary by 8 degrees box to box static to strobe, so 9 degrees difference is definitely possible static to strobing. The Pazon is an improved copy (ref low voltage running) of the Boyer MK3 and the Boyer MK4 has similar improvements so you would expect similar timing variations.

Blue pipes are a sign of retarded timing if the mixture is good.

Submitted by richard_potter on Sat, 15/10/2022

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Hi John,

When I reset the timing I did it statically per the Pazon instructions to start with then checked it with a strobe.  Strobe confirmed the static timing was correct.

Submitted by tony_ripley on Sat, 15/10/2022

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Are you confident that whatever you are using as the reference is correct. By this I mean your 31 degree line etc? How are you strobing?

 

Tony 

Hi Tony,

Good question.  That was one concern i had when I checked the timing originally so I checked TDC with a dial gauge and then used a timing disk to check the calibration scale on the chain case before resetting the timing.

Submitted by john_holmes on Sun, 16/10/2022

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Using a Dial gauge is not an accurate way yo find TDC due to lack of movement of the piston at TDC plus piston rock, you need to use a piston stop to say find 20 to 30 degrees before and after TDC and then use a timing disc to split the difference.

Submitted by richard_potter on Sun, 16/10/2022

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I took the bike out for a short run this morning to take advantage of the weather.  She seemed to run well and looking at the spark plugs afterwards they were a good colour so there can’t be much wrong.   when I was setting up the timing with the strobe I probably ran the bike in the workshop for about 10 minutes in all so I wonder if that, combined with a potentially rich pilot jet setting, meant that the headers got overly hot and hence the discolouration….

Submitted by ian_soady on Mon, 17/10/2022

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... likely although pipe discoloration is more often due to weak mixture.

Submitted by alan_osborn on Wed, 19/10/2022

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Are we sure the Rotor marks are correct? Yes do check TDC and then convert this to a static mark in line with a Rotor mark. Then timing disc in line with Rotor line. The timing plate on the primary cover is known to be suspect. Slot in Rotor can be suspect so relying on the Rotor to be questioned.

Rich pilot jets would cause cooler running, so not a cause of hot running.

 


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