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Old 09-05-2012, 01:50 PM   #31
disston
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I think it's the Dyna III (made by Dynatec) that most use to cure the double image. That is if they are going to use the electronic ignition conversion to cure this problem. There are two magnets for the Hall sensor and they are set separately. I had the hardest time getting this to work and eventually had to use another method after I blew the module up by trying to balance carbs by removing plug wires. (with any electronic system do not balance carbs by removing plug wires) (we are supposed to not ever do that with points/condenser systems either, but for different reasons)

There is another method for curing the double image. It is not exactly fixing the original problem sort of thing but it is closer to fixing the original problem. Here is a page from Duane Ausherman that talks about the whole issue. His article is about the /2s but then he explains the differences for the /5s and the basic idea is what's important anyway. After you read this if you want to discuss it more then we'll start on that.

http://www.webring.org/l/rd?ring=bmw...duane%2Fbmw%2F

Like I mentioned, I tried the electronic conversion like you are planning and this is maybe the most common solution for most but I had trouble with making it work and ultimately I was happier I think with being able to keep the points and later adding a Booster box which has some advantages over the Dyna III. (Booster costs about $80, Dyna III cost almost $300) ( just a guess really)

There are several other people here who went with the Duane Ausherman method of fixing the double image. They'll be around shortly.
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Old 09-05-2012, 05:08 PM   #32
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I read Duane's page long ago, but didn't have the balls to try it.

But I just went out and measured my point gap at both lobes of the advance, and sure enough one was tighter. My points (which, by the way, are made in China...) seem to angle towards each other just a little, so I could tell based on how far the feeler gauge slid in before it encountered the slightest resistance.

Got out my punch and hammer and tried Duane's method.. and I seem to have the point gap now equalized, but my double timing issue is still occurring. It's funny though, the region between idle and full advance seems to be steady - i.e. as the S idle marks leave, they become one image (and the sound of the engine changes, it seems to get more even), and as the full advance dot comes into view it's also steady and one image, then it becomes dull and two images, about 10-15mm apart. Maybe one the pins that control the stop and start position is bent?

So.. I think I'll try swapping back my old advance with pitted lobes and see if anything changes.

I'm liking the idea of an alternator-mounted electronic ignition so there's no way there can be a double image, and I can leave the points in place in case it fails, so swapping back on the road would be easy. Maybe it's time just to bite the bullet. But what if it's somehow my coils? ergggg
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Old 09-05-2012, 05:36 PM   #33
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I haven't been keeping up with this thread but it sounds like you might have a worn out timing chain?

My dad use to bang on the cam with a plastic mallet, start it up and go by the timing light but he use to do it all the time way back in the day.
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Old 09-05-2012, 05:58 PM   #34
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that's a possibility, though I'd be surprised at 32k miles. Is there a way to check for this?
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Old 09-05-2012, 05:58 PM   #35
disston
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SS is right. A bad timing chain can be so loose that it presents a double image. When I had this problem I did the timing chain before I tackled the cam tip for just this reason.

There is also the issue of the large gear on the cam end of the chain. These are not supposed to go bad. I don't like that. They don't want me to change the large gear? But they do not have a reason I can accept for the uneven firing. And the cam bearing, nobody ever says to change the cam bearing. Why not?

There's a lot of stuff on this issue. But nobody seems to know why it happens.

It is most important what it does at full advance. I rode mine with the double image for quit awhile.

I also like the idea of a crank mounted distributor. I had one. I got rid of it. I decided I didn't like the electronic advance idea. There may be nothing wrong with it but it wasn't for me.

This was also several years ago and the units available were rather flimsy. I think they are better constructed now.
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Old 09-05-2012, 06:53 PM   #36
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BMW Bing Float Tool

Quote:
Originally Posted by photomd View Post
I didn't worry about it. I just pulled the bowl, emptied it, filled the bowls using the petcock, turned off the petcock and removed the bowl. I immediately set the bowl in the level concrete in my garage, took my venier caliper and measured it. I think I just held the bowl in place while filling it...just make sure it's full seated so you get a good reading. I think it took 20 minutes to do both carbs.
Every time that I have compared results by measuring the fuel height in the bowl after setting my floats using the float horizontal dribble on/off adjustment method the fuel has been low vs. the published "ideal" height. With the 32mm Bings on the R65, R100RT and R100R I have owned/own the typical measurement has between 21mm and 22mm. For a long time I have used the fuel height in the bowl method. The picture shows the simple tool I made which makes measuring the height a cinch. It is a short piece of stiff wire (actually piece of coat hanger) with a notch at 24mm (28mm for 40mm carburetors).

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Old 09-05-2012, 07:49 PM   #37
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Quote:
Originally Posted by R100RT Mark View Post
Every time that I have compared results by measuring the fuel height in the bowl after setting my floats using the float horizontal dribble on/off adjustment method the fuel has been low vs. the published "ideal" height. With the 32mm Bings on the R65, R100RT and R100R I have owned/own the typical measurement has between 21mm and 22mm. For a long time I have used the fuel height in the bowl method. The picture shows the simple tool I made which makes measuring the height a cinch. It is a short piece of stiff wire (actually piece of coat hanger) with a notch at 24mm (28mm for 40mm carburetors).

I always get around 22.5mm doing it that way. Time after time with no problems whatsoever. AFAIAC, 22.5 is what it 'should' be. I call it 28/32nds. I have been making that measurement with a machinists ruler for decades. It wouldn't be the first time my experience does not add to snowbums but at least his 24mm height will work.
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Old 09-06-2012, 10:11 AM   #38
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has anyone ever ground off one of the cam lobes on the advance and installed a second set of points 180 degrees opposite the first? Then run a second condenser and a 12v coil for each spark plug? If the second set is adjustable it should be easy to dial in spark on both cylinders, and it would be unaffected by imbalanced advance or bent cam nose.

Just a thought..
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Old 09-06-2012, 10:46 AM   #39
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has anyone ever ground off one of the cam lobes on the advance and installed a second set of points 180 degrees opposite the first? Then run a second condenser and a 12v coil for each spark plug? If the second set is adjustable it should be easy to dial in spark on both cylinders, and it would be unaffected by imbalanced advance or bent cam nose.

Just a thought..
I suppose that would work. Not a lot of space there but you might make something like this work.

But I have never heard of anybody doing something like this on an Airhead.

Ordinarily a dual point ignition does something different. It makes the points last longer and work better at higher RPM. They do this by have one set of points handle the function of closing and the other set of points handle the function of opening. Mallory still makes V8 distributors that have dual points. Had them on a pair of Ford 427 motors in a boat a few years ago.
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Old 09-06-2012, 10:56 AM   #40
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Quote:
Originally Posted by disston View Post
I suppose that would work. Not a lot of space there but you might make something like this work.

But I have never heard of anybody doing something like this on an Airhead.

Ordinarily a dual point ignition does something different. It makes the points last longer and work better at higher RPM. They do this by have one set of points handle the function of closing and the other set of points handle the function of opening. Mallory still makes V8 distributors that have dual points. Had them on a pair of Ford 427 motors in a boat a few years ago.
Not sure what's being said here but British twins typically use/used two sets of points. Later BSAs used 12v coils and independent systems giving a long dwell time for the coils to energize. Some Triumphs used 6v coils in series with a wasted spark meaning that each cylinder could be timed independently but both would fire each revolution.
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Old 09-06-2012, 11:38 AM   #41
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Mmm I've never heard of a dual point setup doing what you're describing Disston, but I do know that most Japanese bikes have this exact setup (Honda CB350 has two sets of points, independently adjustable on the valve cam). I guess a longer dwell time is a bonus, as there would then be no wasted spark.

Anyway.. I swapped my old advance in, tried indexing the advance to the left or right of the minimal slop caused by the flat on the cam, and no changes.


I'm doing it.. I'm getting a Sachse alternator-mounted electronic ignition. I like that it uses photo gates as opposed to Hall sensors, and I can keep my points in place to save headaches if it quits. Not as expensive as SH, easier to get than Omega. Just hope it's not my coils or timing chain causing the issues.. apparently there's no easy way to tell if the timing chain is worn on pre-canister models.
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Old 09-06-2012, 11:52 AM   #42
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Off the beaten path, that's all. Should be my middle name maybe.

Yes many bikes use a separate set points for the other cylinder and therefore it can be independently timed. Great idea. I do not know why somebody has not made an after market system like that for our bikes. Maybe it's just a mater of not enough space? It's the only reason I can think of that I've never heard of this being done.

Dual point distributors in V8 cars do work the way I described but it doesn't have anything to do with what you were asking. File this in the round file.
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Old 09-07-2012, 11:04 AM   #43
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float height

Well, it turned out to be my float heights. I adjusted for 23mm and it runs like a champ once again. Ran up to 90 and held it there for a while and no more stumble. It stuck me as strange. I rescued this bike and did a whole bunch of work on it before getting it on the road in 2010.

Question is: What would cause this problem to come on so suddenly?

Thanks for the thread, we're all in this together.

Off to the Sipapu, NM Beemer Rally ! (in the nick of time)
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Old 09-08-2012, 08:30 AM   #44
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chobro, thanks for getting back to us!

Possibly a weather-related issue? Hotter days, less humidity brought the lean condition over the edge? My issue was (way) worse on certain days.
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Old 09-09-2012, 02:56 PM   #45
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No problem senator.

Made it up to the rally and back with no issues, the bike ran especially well since the air was a bit cooler. I won oldest bike ridden to the rally ('76, it was a tie with one other rider), which is just sad.

I'll order some new floats this week. Apparently they get heavy with age and the tabs need adjusting to maintain the correct height. At the parallel position, my level was at 17mm.

Hope you get yours figured out soon.
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