Magneto/ignition timing problem?

[LJ.]

Dohhhh!  Always the simplest things eh? Thanks for a good readup at your expense. Good Lesson for us all.

[bsa- bill]

Well done Terry, don't worry we have all learnt some of the stuff the hard way and the rest from others who learnt that the hard way.
Now we just need some good weather

[pato08]

Hi All

I have coppied this tread, printed and saved to my ever expanding file for garage wall read for my rebuild

My thanks to all for some very enlightning facts

Pato

[groily]

Great news Terry. And even if it might not have been essential right away, having Tony C do the mag can only be good - one thing not to have to worry about ( as long as that cable stays free!) Just in time for the next blast of cold weather then!

[JohnH]

Well done Terry.

I found your recorded experiences really enlightening (I was going to say enjoyable but realised - just in time that it might be misconstrued!). Like Pato, I've stored away the thread for future reference. Really good learning points and I really don't think I would have been as observant or intuitive as you were. Tony Cooper sounds like a magician .... as does Groily ... I would not attempt to take a mag apart - even with his instruction set.

Well done ... as somebody else said - Bring on some decent weather!!

John

[redbeeza]

Thank you for the comments chaps, it really helps to have a pat on the back for persevering, even if it is only via the web.

A big thank you to Groily also, who gave me encouragement and sent me a hand-crafted device for getting the mag bearing inner race off.

I'm still in the dark over how some of the symptoms were caused by only the throttle slide being open too wide. Why would that make the mixture fire in the exhaust rather than the combustion chamber?  I've read in the Amal literature that having too weak a mixture can cause 'banging in the exhaust' but I can't see why. If it was late ignition timing or valve timing out, I could begin to understand. Can any of you technical boffins explain?

Also, I can see that the mixture might be weaker on start-up because the throttle was open too much, so more air was being allowed in. But surely this shouldn't be the case, because the mixture is metered throughout the throttle operation range by various methods: first the pilot jet; then slide cut-away; needle position; and main jet. If the throttle was open too wide so that the pilot jet couldn't meter enough fuel, then the slide cut-away would take over, wouldn't it? Does this make sense, or have I talked myself up my own exhaust pipe again?

I think I can understand the running on one cylinder though. It looks, from the old plugs, that the LH cylinder runs a bit richer than the RH (and I've read the threads about the 'bias gasket' issues), so maybe this was just exaggerated under these fault conditions to cause the cylinder to flood quicker and douse the plug.

I agree about COME ON with the decent weather. I need to be able to get to the MOT station before the bike decides it wants to hibernate. Must bolt the battery down better first though...

Terry

[iansoady]

If the air slide was working correctly it's possible that you were getting something approximating the correct mixture even though the throttle slide wasn't going all the way down.

I always listen for the tap of the slide on the throttle stop screw to make sure the slide isn't hanging on the cable like yours was. If you put your finger on the throttle stop you can actually feel it making contact.

[bsa- bill]

anybody know about how much of the cutaway should be showing when throttle is closed - is Amal tuning picture about right or is it too much of a variable to declare.
Just trying to get starting sussed on the project, seems to be a totally different method needed to that if the flash

[groily]

A pleasure Terry - and glad it worked.
A while back we were discussing the tools required for getting these bearings off easily, and MG kindly dug out a link to a very excellent German-made chuck-puller, capable of extracting a variety of such small races - up to about 30mm if memory serves. However, they are very expensive, and in any case obviously don't offer an easy means of protecting the brass taper on the cb end of a mag. I didn't buy one. But I've made several, and continue to think it's something the people who make all those pullers for various mag pinions, camshaft gears etc etc ought to add to their list of 'useful possible new products'. After all, pulling a mag bearing race is a simple little thing, and there are gazillions of K series mags out there, with loads of capable owners. Wrapping copper wire round the bearing track and whacking armatures wiv 'n 'ammer (often suggested!) ain't the answer. Plus the fact that other devices also obviously use 15mm and 18mm bearings - Magnéto-France 'Double-Débit' dynamos as but one example I've come across lately from a world adjacent to our own.

[Alan @Ncl]

I am just working my way through Maggy threads and read this very informative sequence which prompted a couple of questions of my own (in addition to the new thread I posted today).  Many years ago I had problems with timing slipping and had eventually to get a new autoadvance as the taper seemed to have worn in the one I got with the bike.  In subsequent paranoia I always used loctite on the taper.  I also slotted the holes in the mounting flange (see pic) to get a bit of leeway for timing adjustment without releasing the dreaded nut.

On eventually removing the autoadvance recently, 30 years on, it took a hell of a pull on the centre bolt (quite worrying actually, as I assume the reaction can only come from the force on the fibre gear teeth).  I wonder if others have had similar issues, concerns or comments?

One other observation.  I downloaded the Excel sheet from audioworld as I have just finished creating something similar.  My version gives the following output:
5/16 = 32deg, 11/32deg = 33.7deg, 3/8 = 35.2deg,  13/32 = 36.7deg.  These seem similar to values I have seen elsewhere on this forum and to get them, I inputted a stroke = 84mm (= 3.31 inches) and conrod length of 164mm (6.47 inches).  However, I note the stroke used in the timing converter sheet is less than this so it gives different answers to mine so perhaps the data in there is for an A7?  We get the same answers if using the same input data (which is reassuring at least).