Strange problem with ignition timing

[Joper]

Hello! Hope i can get some help from some of you.

Im doing a tuneup on a r75/7 and have some trouble with setting the ignition. The bike has the original points system. The springs on the advancer is very weak so on idle the mark flickers up and down, still runs good on idle but not perfect (hasnt overhauled the carbs yet and they look like crap!)

The problem is when revving to full advance its impossible to find the F mark. When setting it fully seated on one side i can barely see it, but still a long way to go and theres no way setting it like that. The gap is spot on (030-040). Ive tried spinning the advancer a bit on the tip of the camshaft (there is some play there) but thats not enough. What could have happened? Ive seen this before on a friends bike but that one also had a bent cam tip wich i tought "helped" the problem. Didnt look into it very much since we fitted a silent hektik on it.

Any tips? The OT mark is spot on when the pistons at tdc so the flywheel is correct.

Best regards
Johan

[Bamboo812]

The dancing timing mark is a symptom of loose timing chain or bent cam nose. Is it random dancing or are there two distinct images at idle? A crank mounted electronic ignition can fix this issue. Not seeing the F mark at full advance; is it just blurry from dancing or does it not show up at all? Not at all would make me think it's a sticking advance unit. Clean and re-grease with appropriate lubricant, if so.

[Joper]

Random dancing, not the two marks usually seen when the cam tip is bent. A crank mounted ignition is not an option for this bike.
I cant see the F mark at all. When the timing is fully set on one side i can just barely see the F mark but its way out of reach for an adjustment to fix it. I would have to file the points plate a whole lot to get it to show. The advance unit is not sticking.

Very strange fenomen to me?

[bbelk]

Random dancing, not the two marks usually seen when the cam tip is bent. A crank mounted ignition is not an option for this bike.
I cant see the F mark at all. When the timing is fully set on one side i can just barely see the F mark but its way out of reach for an adjustment to fix it. I would have to file the points plate a whole lot to get it to show. The advance unit is not sticking.

Very strange fenomen to me?

Sounds like a very worn timing chain. I was having to file the points plate to get mine into adjustment until I replaced the chain. It helped with the fuzzy timing marks as well, but did not eliminate them.

[Kurt in S.A.]

Where's the S-mark at idle? Do you watch the F-mark as you slowly raise the RPMs?

Note that the gap doesn't have to be "spot on"...it can actually be as small as 0.012" or as large as 0.022". Try readjusting the gap one way or the other so that you can then rotate the points backing plate to get the F-mark back where it's supposed to be.

Kurt in S.A.

[Joper]

I sorted it out by filing the points plate. Guess the camchain is worn like you said! After a carb overhaul, sync and a ignition that's properly set this bike runs sweeeet!

Thanks for the help!

[Duane Ausherman]

1. You could have been using an improper light.

2. Did you use a spark gap adjuster to force the spark to be strong?

3. You never mentioned shining it on the advance mechanism itself to see what is really happening. A bent cam tip shows up easily this way. That is very important. Did you paint the "F" mark with white paint?

4. Did you use Google to find the related articles?

There is so much more to this issue. I am glad that you found it easily.

[Joper]

The light has worked on my other bikes without an issue. New spark plugs with set gap. No bent cam tip. Didnt paint the F mark, no problem seeing it even without my glasses Googled but didnt find anything usefull. I didnt have the cam chain in mind when i first found the problem. Now when i know it its pretty given thats the problem. The bike has probably the original cam chain and hasnt been worked on for long.