to expand a bit on Scots comment: the timing is set at full advance and you have no choice about what RPM full advance happens unless you open up the bean can and modify some things. The RPM for full advance is built into the mechanism. So you can forget RPM and just rotate the beancan until the Z mark and the crankcase mark line up.

You do have to wind the engine up enough so you are in the range of full advance. Won't work at idle. Try 3500-4000 rpm. You should be fully advanced by then.

I loosen one screw on the beancan and tighten the other so i can rotate the can and it will stay where I set it. Then I drape a blaze blanket over the nearside header so I don't fry my arm on the header (again), wind up the throttle and lock it with the throttle lock screw then rotate the can to put Z on the mark. Shut down, tighten beancan screws, disconnect battery ground and sew it up.

https://www.lowes.com/pd/Oatey-Soldering-Flame-Protector/1043403?cm_mmc=shp-_-c-_-prd-_-rpe-_-google-_-lia-_-142-_-plumbingconnectionsandsupport-_-1043403-_-0&placeholder=null&gclid=CjwKCAjw34n5BRA9EiwA2u9k312EQJ796rQG7GyUdVwKUTQwRZMtuLqntl0HYsFh9Z4wm7zXXmsewRoCoSIQAvD_BwE&gclsrc ="aw.ds"

Thank you both.
Craig

► Full Advance is a function of the particular ignition type and brand you have on your bike. Don't forget, we're writing for the larger audience here, which represents 5 or 9 different ignition systems, both stock BMW and aftermarket.

► Your strobe will show you where your engine reaches Full Advance. As you watch the timing window and slowly rev the engine progressively higher, various timing marks will come into, or go out of view. When that progression of marks stops, that is, when the next 100 higher RPM fail to make the marks visually advance... then you have found Full Advance. That is the definition of Full Advance: The engine speed at which the ignition ceases to advance the ignition timing. The strobe lamp simply does the visual "stop motion" effect, which allows you to see this happening.

► The strobe will also show you how good or worn your ignition unit is. If your view of the timing mark is dancing all around in the window, forcing you to do some kind of mental averaging, then you probably have a mechanical advance system... and now you see how bad it can get with 40 years of wear on the advance mechanism. Or, if the timing zooms from Full Retard at idle right up to Full Advance at a very low point (say for instance) 2200 to 2500 RPM, then you can see that your advance springs are shot (stretched out due to age). This because it's the springs that resist the mechanical movement toward Full Advance.

All this as opposed to the latest Electronic Ignition (EI) unit, which will present a rock solid visual of the flywheel timing marks. And this is because the "advance" is a pure mathematical calculation done within the EI software. And since software doesn't wear over time or need regular lubrication, its ignition position is highly stable.

Hope this helps

I'm an old man, disabled and my hands shake badly. It is difficult for me to type so I leave the long dissertations on every conceivable situation to snowbum and the like and just answer the OP's problem or question about their bike. I send a short dissertation to Bob occasionally about errors in his dissertations, and they are very few. I am writing for the person who asked. if you wish to publicly include me in a "we're" please consult me back channel first. This gives me the opportunity to bow out if I disagree. Oak alienated a lot of people and I noticed years ago that there was an 800 lb. gorilla in this room too. have you noticed? (hint: where is everybdy?)

Off the top of my head I can think of three ways to determine maximum advance. Two are slow and one is fast. You covered one of the slow ways, I thought I would throw out something about one of the fast ways. Something I have leaned from the pro mechanics is how to be a whole lot faster. Speed = making flat rate or better = making a living. I'm sick of wrenching. I've been doing it a long time and it has gotten old. Fast = more riding time.

If one is truly going to write for the broader audience then one has to mention that some bikes are not timed at full advance at all, they are static timed. When a magnetic, inductive, optical or Hall trigger is used in place of points the bike is timed at full advance. Points are static timed. It is possible to static time the others but one must build a gizmo to display the state of the trigger.

Years to not wear advance mechanisms. Miles and poor maintenance do. When one is worn it wears symmetricly The classic double image on a points bike is a cocked cam nose. I do not know about the newfangled units with all the plastic parts. I could see one of those just blowing up. I protect mine with exotic lubricants. I have never seen stretched springs caused by anything other than hamfisted wrenching. The advance should not be disassembled unless one knows exactly what one is doing and has a good touch. !00k+ miles and the springs were like new. But I haven't seen everything.

Gentlemen thank you all. I really appreciate you taking the time to respond. Multiple responses often add different perspectives and for me, can lead to an ‘ah, now I get it’ moment. Despite being an active enthusiast for 6 decades my work forced me to reach for my wallet for all but the simplistic tasks. Now that I have some time I find it rewarding to learn more complex tasks. The hardest part for me is learning patience and to ask for guidance.

My old brain likes simple steps... I.E. step 1, step 2 etc BUT I also like to understand why I am doing something. I simply don’t have the patience to work my way through Snobum’s site and the ability to ask a question here and get an answer here - in an apparently small and welcoming community - is welcome. On other BMW focused sites Airheads.org is well known as a premiere source of airhead wisdom.

Now it is time to finish morning coffee, disconnect the battery and get the bean can exposed. Thank you all again.

Craig

A final quick note to say thank you. An enjoyable 90 minutes in my shop listening to rain and correcting the timing advance. I now have a steady Z perfectly centered at 4,000 rpm. The Z is rock solid - no jumping around. I would not have tried doing this without your guidance. (Arni your hint re burn avoidance allowed me to avoid scorched meat). The rain has stopped. Going for a ride.

Craig

So how does it run?

That trigger and advance setup is pretty set and forget. You can mark the can and case with marks from a sharp punch so if you have to pull the can (replace o-ring or plug, clean+ lube pivots, etc) you do not have to re-time it.

@ 4000rpm you should be well up past minimum rpm for full advance. But it is worth knowing what that minimum rpm is, that is, the minimum rpm required to just hit full advance (Z centered in window). As Wobbley mentioned the springs can go south and this will lower that minimum rpm. Easy to suss it out. Pull timing plug, hook up timing light and wind up the motor until the Z mark is first centered. Observe RPM on the tach. Record in your service log. If you have to Dx an ignition problem down the road you might want that number.

It is running very well. After I set timing I did it careful carburetter mixture adjustment as well as carefully balance the carbs and cables. It feels like a new bike.

Good tip on noting minimum/maximum and keeping a record.

Cheers
Craig

There is the slowest RPM at which the beancan hits maximum advance. But once it is at full advance that's it, it stays there as fast as you want to run the engine.

I've got a kit sitting on the shelf for my Trail 90 as I write this, waiting for a Round Tuit to finish the job.

You've got a Trail 90 ??? My admiration for you just increased. 😛

That was way back when you could "Meet the nicest people on a Honda".
Although there was another dealer in town who swore "You get more nukie on a Suzuki". 😆