Motorrad Elektrik Ignition

[Seth]

On my Mystic, I found the bike idled high but it disappeared when I found the intake manifold was loose in the head. After tightening it and rebalancing the carbs, my bike keeps a constant idle.

[Gibson]

Thanks barryh, I agree with you. If it was not too lean before, why should it be now. I think the test is, if the idle mixture screw can be set for max idle speed, then backed off a hair the idle jets are correct. Plug readings have always been good (not too lean).
The thought did cross my mind that the the advance was occurring too soon with sacked out springs.
My bike is a R100R Mystik. (fancy R100R). This is among the most mildly tuned airheads. CR is low small carbs etc. The bike only pinged one time after sitting in horrible traffic and it was super hot. When I switched route and took off it pinged slightly so I backed off a bit. As it cooled off the pinging went away.
It is getting mighty cool here now, but I am going to try setting the high rpm timing mark in the upper half of the window. I think that should help. Thanks again.

[Kurt in S.A.]

Just curious...did the Mystik have advance springs? I know they transitioned to the bean can and hall ignition/electronic ignition, but am not certain about the springs. In any case, you can determine if the ignition is advancing too quickly. Just use a timing light and find the RPM at which the F-mark appears in the window. Should be around 3-3.2K RPM. If the F-mark goes past the window, that's another problem.

Kurt in S.A.

[Gibson]

Hey Kurt, all airheads had mechanical advance. In 81' they went to the Hall triggers to replace points but retained the mechanical advance. I had the same problems with my 81' R65 and my 93 R100R. For some reason, when they get good and hot, they hang up. I am planning on rebuilding the advance in the "bean can" as a back up. I would be interested in seeing what was going on in there anyway...

[Wobbly]

I have not been able to locate these anywhere...any ideas on where to find different size jets for the Bing 32mm carbs?

I don't think you've told us what model the bike is but I'm surprised to hear that richer pilot jets were suggested. That fact that they don't seem to be available suggests they are not normally needed on a stock bike.

BarryH is right on the mark.

► Here's what I would do and have done. The closer the USA bikes get to year model 1995, the leaner the EPA made them run the jetting. This is great for bureaucrats, but bad for your engine, and bad for performance. Lean engines don't respond well to throttle and run much hotter (which forced liquid cooling on BMW and spelled the end of the Airhead for us).

I would look at the available Bing data in a) your manuals and/or b) in the Bing data book for 1) older models OR 2) European models with the 32mm carb. (In essence you are looking for non-EPA jetting data.) What I found was that it was the needle jet that got leaner, not the idle jet. So I've enlarged the needle jet on both my R100's to what the German's ran in 1980. I've got a beach sand tan color on my plugs, and the bikes have far more low-end grunt and much, much smoother acceleration.

Now here's the gotcha about needle jets... Unlike the idle and main jets, the needle jet has a needle literally banging around inside it, which enlarges the needle jet and reduces the needle diameter. Both these make the carb run richer like you want, but more pounding takes place at low speed, so the enriching effect is NOT constant across the RPM spectrum. To return to any type of sane fuel mixture control on your 20 year-old bike you MUST replace both the needle and the needle jet. That's simply a function of age and should be done on any older bike. But I think you'll also discover that older, pre-EPA bikes with your displacement also ran a slightly larger needle jet.

► And too, do not overlook valve adjustment and carb synchronization. Carbs need to be synced at 1000 RPM at the idle screws, and then again at 1500-2000 RPM at the cable adjusters. If you don't have a carb sync-ing tool, you can build one yourself with clear tubing and ATF for under $10, and it works great. Do It Yourself Carb Sync Tool

► Don't forget the high RPM timing set using the "F" mark. The Boyers and Pazons I work with generally don't stop advancing until around 5000 RPM !! So read your installation manual carefully for the details. Remember... you can forget anything you ever knew about points when you install EI. It's an entirely new ball game. Sort of like trying to apply what you know about American football to help you understand World Cup soccer.

Hope this helps.

[SteveD]

Some will remember Fun Holiday. From my memory he used to bang on about smaller main jets and a more lean setup aiding power.

I can't remember his discussion re: the needle & jet though, except that they're a wear item and should be replaced occasionally. He did write about needle wear etc.

[Wobbly]

Some will remember Fun Holiday. From my memory he used to bang on about smaller main jets and a more lean setup aiding power.

Depends upon where he was from as to whether the information applied. A person riding in the arid areas of southwestern USA (100º+F) needs to run slightly richer than a person riding in, say for instance, Scotland (70ºF). From the Bing data it's clear that BMW jetted bikes differently for sale in different parts of the world. Some of that was forced by law, some forced by local temperature conditions, and some by local fuel issues.

There IS far more power in a somewhat leaner mixture than what I was taught was "right" back in the 1960's. Back then you wanted to see a brown plug; these days an air-cooled engine wants a light khaki tan. But there is also a clear difference between "power" and "longevity". As I visit more and more BMW rallies, it's very clear to me that the model years with EPA lean mixture engines are highly UNDER-represented. The overwhelming majority of what I'm seeing in the southeastern US is pre-1983 bikes.

[George Ryals]

Idle hang up on a fully warmed up (20-25 miles) engine can be caused by too lean idle mixture.

[SteveD]

...Depends upon where he was from as to whether the information applied.

California, where opinions are strong and his was solid!

[Gibson]

Thanks. Lots of great info! I checked the timing again last night for both S and Z. Checked "Z" at 3400rpm per instructions with ignition. That is where advance is peaked I guess. Looks like timing is slightly retarded. I have a feeling a few degrees more advance will make it beefier in the lower mid range like it was before. Because of the bikes relatively low compression ratio, and I use premium fuel anyway, I think a hair more advance than specified will be fine. As long as its not pinging. I will look into the Euro spec needle and needle jet. That sounds like a great idea in any case.