Boxerworks.com

1973 R90/5

Checking the timing with a strobe, I find that the "F" mark has gone way past the window at 3500+ rpm. At idle, the spot near the "F" mark can just be seen below the bottom of the window, about 1" below center. All of this is with the timing as retarded as the points plate will allow. What's up wit dat?

The bike starts easily when cold and runs like a champ with no pinging. When starting hot, it struggles just a tad to get over the compression, as if the advanced timing may be impeding it(?).

Anybody else have this or similar issue?

I would check the weights, pivots, etc.,and put some NEW springs on the advance unit. Then have another look with the strobe.
You COULD file a longer slot in the points plate, too...but when you get to the extent of the stock slot, it usually indicates you timing chain is worn plum out. OR the tensioner is not tensioning as it should. No pinging is somewhat curious as it may accompany these conditions, but anything is possible with a /5.
{ain't it the truth, guys?]

I saw you lurking, Jean. Hoping you would respond.

The timing chain is new. The timing (marks) seems to be way off at idle, too. The springs were renewed with the stiffer ones less than 5000 miles ago.

I have tried two different advance units (0 232 002 007 & 0 232 002 012) with the same symptoms from both. The 007 unit had the new springs, the 012 is now installed.

There was a bad run of points a couple of years ago and the rubbing block was found to be about a millimeter and a half too long. You couldn't get it timed and was all the way to the end of the slot. They apparently have this resolved now. Measure the height of the rubbing block and check against another known set. This drove me crazy until I figured it out.

I can see how the height of the rubbing block would affect the point gap and thereby the timing, to a small extent. But, the point gap adjustment is approximately in the middle of its range, before I set the timing.

Having thought of this subject prior to posting here, I could give this scenario much more credence if the position of the rubbing block were off, rather than the height. All of my point sets (5) appear to have the rubbing block in the same position.

I have another set of points bought at the same time from the same source (Hucky) in my '77RS, without this issue.
I don't mean to be contrary, and I'm not too upset since the bike runs so well. I'm just curious if others have seen this anomaly and what they did to correct it, etc.

As the rubbing block wears down the timing retards, so if the points are too far open would they not be too far advanced?

Yes, that is my thought. Too tall a rubbing block will open the points sooner, and ultimately further. This issue is moot once the point gap has been corrected. My gap is correct and the adjustment is in the middle of its range. A misplaced rubbing block would change the timing, regardless of the point gap via the height of the rubbing block.

When you changed the chain, did you change the sprokets, or did you change at least ONE of them (the little one) ?
If the marks are off at idle, and you are at the end of adjustment, AND the rubbing block is OK, you are going to have to consider the basic mechanical timing again.
THERE. I said it.
Actually I hope that isn't the issue, but all other things being in order, it's the only thing left to do.
Before I changed the chain on my 78 R100s many years ago, I DID achieve proper timing with an additional 2+ mm of slot filed in my points plate. I had to get a new crank-sproket when I got the new chain, tho. The old one had rather sharp teeth and that would have pretty-much wasted all the work if I had continued to use it.

New crank sprocket with the new chain.

So, after all else failed you had to file the slot? I just didn't want to be first.

With your new crank sprocket was the elongated slot superfluous?

Did you get the correct sprockets? In 78 they advanced the cam timing by 6 degrees. I believe they did that by moving the key slot in the cam sprocket. If you got a 78 cam sprocket then maybe that's the isue.