Ignition issue squared

[rjavocado]

When I test drove this bike, it seemed to run fine. It started right up (from dead cold, I checked to make sure the seller didn't pre-warm it to make it start easier), and ran great on the little test drive I took around the neighborhood. I read up on the model, liked it, and bought it.
It did fine running around town at moderate speeds, I gave everything a thorough looking over and decided it was safe to take out on the highway to see what she could do. Aw crap. Once it got up into the upper third of the rpm range, the engine seemed to bog down, loose power. Plenty of power at low revs (seemingly anyway, I don't have a basis for comparison, never having ridden a CB750 before).
Then it became harder and harder to start until she wouldn't start at all. I checked for fuel flow, seems fine on all four carbs when I unscrew the drains on the bottom (forgive me for any poor jargon, I am a bit green). I installed new plugs, checked for spark, and the plugs I checked seemed weak

[Yoshi823]

Welcome to the forum for starters...

It does sound as though you've set yourself a task, & that you've lost some enthusiasm for working on the bike during the Winter months.
I'd start by draining the fuel from your tank & putting it in the car. While the tank is empty check the fuel filter then perform a flow test...if the flow slows down after a few seconds of draining some petrol into a suitable container, the fuel cap breather might be blocked.
Then flush some new fuel through the carbs. Hopefully the new charge of fuel will remove any sludge that may have had time to accumulate in the float bowl. Once you've had the bike running afterwards you'll know whether you'll have to pull the carbs off & clean them out.
Before suspecting the ignition system that came with the bike i'd have thought about something like the valve clearances...something that from your procedure when you first bought the bike you don't appear to have checked. If the clearance was too tight, the bike would suffer from the way that you have described. The engine would run ok from cold, but as the clearance tightens as the engine comes up to operating temperature, the valves could stick open slightly, lose compression & be difficult to restart.

Have you got a manual for the bike? The Clymer one is good, as is the Haynes.

[Sprunghub]

I've just fitted a full Dyna S set up to my F1, if I can help, I will.  Probably be good to know what wires you see that aren't 'stock' ?

[Sprunghub]

http://www.hondachopper.com/garage/martek_440/martek_440_1.html

May help explain what you have.....stock wiring is pretty simple at the "points" end, because it comes with your Dyna S ? ie one yellow, one blue & one red.  Just need to know what the wires at your coils look like ? 

[rjavocado]

Thanks for the replies folks!

Okay, I drained the tank and filled it with fresh fuel. As Yoshi823 suggested, I decided to set the valve clearances before trying again to start the bike. Trouble is, upon removing the points cover, I can't locate any markings to indicate when the pistons are at TDC. Are these marks part of the original (now removed) points plate assembly? It's hard to tell from the illustration in my Clymer manual.
Here is what I see:



Without these marks, How to I know when each piston is at TDC? I'm guessing that if I remove all the tappet covers and watch until both valves are closed for each cylinder, that this will indicate close to TDC for that cylinder, but this doesn't seem accurate to me. I've researched all around and can't find any info on adjusting valve timing with aftermarket ignition. Am I missing something here?! Please help!

@ Spunghub: Thanks for the link! I'm sure it will help quite a bit when I'm ready to switch out ignition systems. I'm going to try like hell to get it running with the Martek first, as I find it unlikely that a 30 year old ignition would just happen to fail right after I bought it (though anything's possible), and because I would much rather install an expensive upgrade on a running bike than one that doesn't!

[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 


 

[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.