SOHC.co.uk Forums > CB750
Ignition issue squared
Sprunghub:
http://good-times.webshots.com/photo/2371625390060737053tXHzWr
http://good-times.webshots.com/photo/2201156860060737053yYGGQg
I think it explains ?
Some horror stories about it 'cooking itself' instantly if wired up wrong & lots of comment about keeping the optical elements clean ?
It looks, like with the Dyna S, as if you keep the advance plate, behind the Martek, & then plug it into that ? The fact that the lug on the Martek is locked into the advance retard, means the timing points are "fixed" ?.....as far as I can see ??
When the two marks line up, it should be bang on.
There's loads to Google on them, quite a few references on the US SOHC Club ? but not all good. There seemed to be a propensity for them to just die.
Dave M:
I considered fitting an electronic system to my CB550 but in view of the mileage I was doing and the cost of the system I decided to stay with the points.
OK they're a bit fiddly but they work fine and they won't just die on you.
rjavocado:
Yeah, Sprunghub, on the Martek instructions you linked to you can see that the rotor clicks right onto the advance mechanism, and that you can see the marks for T 1-4 etc. right through the peephole in the ignition housing. How or why mine was assembled without the advance mechanism is beyond me. Fortunately, the previous owner gave me a couple boxes of spares, including the original points plate and I found this, removed the cam as per Martek (and Dyna S) instructions and cleaned it up:
So tomorrow I'll take it apart and reinstall it correctly. And yes, it looks like setting the ignition timing really is as simple as lining up the two marks. That done, I'll set the valve clearances, get some fresh fuel in the carbs and give 'er a try!
Sprunghub:
Excellent - no wonder it won't start :o
rjavocado:
Upon further investigation, I found that the ignition advance mechanism is in fact there, but the Martek's rotor covers it so that you really have to look down into the peep hole at just the right angle to see it! So I checked all the valve clearances (the were all just right as it was), ran some fresh fuel through the carbs, and lo and behold! she fired right up first try! As startling and mysterious as the bike's non-running condition in the first place. Next, I'll double check fluid levels, tire pressure and chain tension, and find a nice long stretch to see if she's still losing power at high revs.
Will update.
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