Sticking Advancer?

[Julio A.]

I had a long ride today where my R65 was subjected to prolonged cruising speeds. The first thing I noticed when I slowed down for the toll gate on the way home was that my RPM was just above 2K and stayed there. Normally, after a long ride, it would just linger at above 2K and would slowly come back to around 1K.

Noticing that my RPM's were not going down, I tried feeding the clutch a little to reduce the engine speed. When I did that, RPM's would remain at 1K. But when I open the throttle a little bit, it would stick to 2K again.

My valve clearances have been properly set, carburetors have been synchronized, and reading the spark plugs indicate good A/F mixture.

First I thought It might be that the engine is running a bit lean, But if that was the case, the RPM would come back up to 2K whenever I lower it down using the clutch. It just theorized it was a problem with the advancer or something.

Since my R65 has the electronic ignition, does this even have a rebuild-able timing advance? I'm looking at a lot of related articles right now and nothing seems to shed light on my problem.

[Barry]

Since my R65 has the electronic ignition, does this even have a rebuild-able timing advance?

The stock electronic ignition has a mechanical advance system same as the earlier points in a can system. It can be rebuilt or really just cleaned and lubricated which might well resolve the problem.  9 times out of 10 though idle hang up is due to carb idle settings and even if it is the advance mechanism it's much easier to eliminate the carbs first before diving into the bean can.

In order to check if it is the idle settings, it helps to understand why it can happen. Carb related idle hang up occurs when the transition ports are brought in to play at idle because the butterfly is too far open.  The transition ports are the two tiny holes right in front of the butterfly's bottom edge. They get fuel from the pilot jet but aren't controlled by the pilot mixture screw, they are controlled simply by the position of the bottom edge of the butterfly. Other than the idle speed being set too high the reason the butterfly might be too far open is that idle mixture is either too weak or too rich and the idle settings needed at bit more throttle to compensate.

Either way the simple test is to move the butterfly away from the transition ports by reducing idle speed using the throttle stop screws on both carbs, even if that means going lower than usual or desired. If the idle hang up is resolved then you know it's carb related and can re-tune the idle mixture. If not then you only wasted a couple of minutes and can move on to looking at the advance mechanism.  

[montmil]

Barry is spot on regarding high idle issues. What catches out many people is doing a carb sync with the engine at less than full operating temperature. Even here in Texas during our normal century-mark summer temperatures, it's necessary to take a 30 mile ride before tweaking das Bingers.

Not saying that ol' Julio isn't hot enough -his girlfriends certainly think he is- but other forum members may benefit by tuning carbs with an engine properly warmed.

[iwSVPyFzWDH]

For my '79 euro delivered machine the answer to this question is, "Yes, all of the above". I had the same issue with the idle hanging after exiting the freeway.

I fully disassembled, cleaned and rebuilt the carbs. When synchronizing be sure that both enricheners close fully.

The bike runs noticeably better but was still hanging. I fully disassembled and cleaned the bean can components then lubed it and reassembled.

Overall engine operation is noticeably smoother now that the ignition advance adjusts freely. Idle hang is almost totally eliminated but occasionally it still hangs a bit after a long uphill haul.

I find the BMW Airhead Carb. Sync. Adapters here,

http://www.northwoodsairheads.com/Tools.html

are invaluable in this process. My high idle issues are reduced to a minimum. When it occasionally still hangs it does not hang at such a high idle speed and it drops to normal idle after just a few seconds. Well worth the effort.