Norton Dominator 99 with K2F magneto

Hello,

Went for a ride today and bike worked good until i went to a highway and rode about 60mph at and bike started to spit back to carb and also popping in exhaust.

I pulled over and changed spark plugs but i didnt help, i could still ride it but soon it got worse.

Got it home and started it up again, it idles okay but soon as i try to rev it it just bangs and pops in exhaust and spits huge flames, wont take high rpm at all. It feels that its running retarded. Its fitted with K2F magneto and AAU.

I took of the timing cover and the bob weights are sticky, i mean that i pull them full advance position and they stay there, theres one point where chain is slightly slacker and AAU works as it should. Lets keep in mind that i dont have timing tool or cut open cover so dont know if its because of no support at the center axle.

I also checked with strobo light that both cylinders give spark continually even though its spitting flames.

So i would guess that either the AAU wont advance at all, or then timing is not correct anymore. What do you think? Could the AAU stick in retarded position? I've read that it would stick advanced position but would the symptoms be that kind if it was fully advanced all the time?

Likely inlet air leak or timing slipped. Timing slips when the AAU taper is not well fixed on the magneto armature.

I'll need to check it tomorrow, i guess i'll need to buy timing cover tool so i can get magneto back to correct tightness if i'll need to take AAU off.

But i'll start with checking for leaks and ignition timing somehow. If i rotate engine compression stroke TDC should the points cap start to open? Assuming its fully retard position.

Thanks for help.

AAU often sticks in advanced position as you describe, especially if magneto drive chain is too tight. Usually this causes no problems except occasional kickback on starting.

Sticking in full retard position would limit the engine from reaching high rpms, but if it failed to advance by centrifugal force, you would find it stuck when removing the timing cover.

Does the engine start and run well when cold? If yes, and if problem develops after engine gets hot, then it is most likely the internal capacitor. Usually the capacitor, when failing, simply kills the spark .... no spitting, coughing, backfires, etc.

Check the timing. Here is how to time a K2F ...https://www.accessnorton.com/NortonCommando/setting-up-and-timing-a-k2f-magneto.19685/

Slick

texasSlick said:

AAU often sticks in advanced position as you describe, especially if magneto drive chain is too tight. Usually this causes no problems except occasional kickback on starting.

Sticking in full retard position would limit the engine from reaching high rpms, but if it failed to advance by centrifugal force, you would find it stuck when removing the timing cover.

Does the engine start and run well when cold? If yes, and if problem develops after engine gets hot, then it is most likely the internal capacitor. Usually the capacitor, when failing, simply kills the spark .... no spitting, coughing, backfires, etc.

Check the timing. Here is how to time a K2F ...https://www.accessnorton.com/NortonCommando/setting-up-and-timing-a-k2f-magneto.19685/

Slick

Click to expand...

Hello,

The bike starts kinda okay cold and hot, and it also idles kinda okay, its not stalling or shutting down by itself at idle.

Its not taking higher rpm at all, if you try to rev it it just bangs and shoots huge flames through exhaust pipes. When i rode it home i could only hit tops 30kmh, really unconfortable to ride..

When i pulled the timing cover off, the AAU was sticky almost all the time, i dont remember if it was stuck at advance. What i mean by sticky is that when i turned the weights to advanced position and released my hand they stayed there at advance, but when i rotated engine from kickstart and happened to find a spot where magneto chain was slightly slacker and the AAU was not sticky anymore and it always returned to retarded state. But could it be only because of the cover was off, or should i consider that thenproblem could be the AAU?

Is it possible to find out if the capacitor is starting to go bad?

The AAU might seem sticky, but if it returns to retarded when you rotate the crankshaft, then it's probably ok.

Your condenser or the whole mag may be knackered, who knows? Don't worry about that yet. Just get the timing checked, then re-set if it's wrong.

And have a look at the condition of the tapers. Does the auto advance stick nicely onto the armature shaft?

Triton Thrasher said:

The AAU might seem sticky, but if it returns to retarded when you rotate the crankshaft, then it's probably ok.

Your condenser or the whole mag may be knackered, who knows? Don't worry about that yet. Just get the timing checked, then re-set if it's wrong.

And have a look at the condition of the tapers. Does the auto advance stick nicely onto the armature shaft?

Click to expand...

Hello,

I started out by taking carb off and threw it into ultrasonic cleaner and i have replacement for the points so i started to change those, also it has new rubbing shoe. Im facing same problem as before that we leafspring is touching the cam ring. Need to work at out and test it.

If its still acting same as before then ill need to start checking the timing seriously. While rotating the the armature from the points side i could see that the AAU returns everytime back to retard pos.

I don't know how to test the capacitor/condenser without taking the mag apart (although I suspect it can be done), but one classic sign of a bad capacitor is when the problems you are having go away after the bike really cools off and then come back after you ride long enough for it to warm up again. The original capacitors seem to all go bad with age, So unless you know the mag has been rebuilt by someone who is competent the capacitor is probably gone as are other components in the mag as well. Verifying the timing can't hurt, although it is a PIA. If the timing has been done recently it is easy to get it wrong. It takes a bit of trial and error to tighten the mag sprocket on the taper withiut having it move and the AAU has to be locked fully advanced. Borrowing a known good mag and seeing how the bike runs with it is a nice test if possible.

Your description of the behavior of the AAU advance mechanism, should be considered "normal", since most seem to do what you say.

Read again Bodgers post #8 above.

There is no way to test the capacitor "in situ", and opening the mag should be left to persons with the proper tools and knowledge. If the bike runs well cold, but quits hot is 99% certain of a bad capaitor.

Your description of flames from the exhaust, and failure to reach high rpm suggests very late timing. This might be caused by an AAU that has slipped on the mag drive taper, but from my experience getting AAU's off the taper, such slippage is doubtful ..... in other words, once they are tightened on, they are on!

Next step: Check timing! As a crude check, do the "spoke in the hole" method, but use a degree wheel to set it up properly. Also, check that point gap is the same on both ramps of the cam ring.

Slick

Bodger said:

I don't know how to test the capacitor/condenser without taking the mag apart (although I suspect it can be done), but one classic sign of a bad capacitor is when the problems you are having go away after the bike really cools off and then come back after you ride long enough for it to warm up again. The original capacitors seem to all go bad with age, So unless you know the mag has been rebuilt by someone who is competent the capacitor is probably gone as are other components in the mag as well. Verifying the timing can't hurt, although it is a PIA. If the timing has been done recently it is easy to get it wrong. It takes a bit of trial and error to tighten the mag sprocket on the taper withiut having it move and the AAU has to be locked fully advanced. Borrowing a known good mag and seeing how the bike runs with it is a nice test if possible.

Click to expand...

Hello,

I do not know history of the bike what PO has done etc. I bought it last year and probably got about 3000km so far and it has worked good until now. I havent touched the timing myself. While watching with strobo the flashing newer stops even tough its not revving so it feels like its not advancing it at all.

I also checked compression for fun and it was about 10,1-10,2 bar left cyl and 10bar for right cylinder.

texasSlick said:

Your description of the behavior of the AAU advance mechanism, should be considered "normal", since most seem to do what you say.

Read again Bodgers post #8 above.

There is no way to test the capacitor "in situ", and opening the mag should be left to persons with the proper tools and knowledge. If the bike runs well cold, but quits hot is 99% certain of a bad capaitor.

Your description of flames from the exhaust, and failure to reach high rpm suggests very late timing. This might be caused by an AAU that has slipped on the mag drive taper, but from my experience getting AAU's off the taper, such slippage is doubtful ..... in other words, once they are tightened on, they are on!

Next step: Check timing! As a crude check, do the "spoke in the hole" method, but use a degree wheel to set it up properly. Also, check that point gap is the same on both ramps of the cam ring.

Slick

Click to expand...

Hello,

I kinda doubt that the AAU would have slipped the taper but if none of things i've done wont help i'll need to check the timing.. I was rotating engine to TDC and the points cap were starting to open close to the TDC so i think the timing might not be that far away.

The bike starts up either cold or hot kinda good and idles okay cold or hot, but either way it wont rev and spits flames out exhaust pipes and sometimes spits flame through carb.

Thanks all for help, i appreciate it.

Just noticed your post comment about the leaf spring on your points touching the cam ring. Haven't looked at a points plate for a while, but I would rule out that condition having an effect on when the points break - especially as the revs rise, before doing anything else. I.e., fix that before trying to diagnose further.

Hello,

Started the bike up and it ran much better and i could rev it up but it last only for second or two. Still not running good.

The leafspring thing is now eliminated and its not the problem.

While runnin it without the magneto cap i can see the points arcing on both sides and when i rev it they stay in the same place all the time. I think that this would tell that its not advancing at all. I guess i can get the enthe engine to run about 2000-2500rpm not more. Next i will check the timing.

I defer to the more knowledgeable, but wouldn't arcing points be a sign of a blown capacitor/condenser? Not wishing you the bad end of the spectrum of possible problems but.....I'm assuming that when you say "arcing" you are referring to the spark "arcing" at the points.

Bodger said:

I defer to the more knowledgeable, but wouldn't arcing points be a sign of a blown capacitor/condenser? Not wishing you the bad end of the spectrum of possible problems but.....I'm assuming that when you say "arcing" you are referring to the spark "arcing" at the points.

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Hello,

Yes i mean the sparks when points open.

I checked timing following the tutorial/manual in the link that Slick has added,

Left cylinder compression TDC and the shoe was approxmently at 5 o'clock and right cylinder comp. TDC and it was 11 o'clock. So i guess the timing is pretty close to right.

So im curious about the blown condenser, id be pleased if someone would confirm that the points are not supposed to arc/spark? If they dont and the conderser is wasted, then i dont know if i have any other choice than pull the mag out and tear it down and replace condenser with brightspark set.

But would these be the symptoms what you could get with bad condenser?

Left cylinder compression TDC and the shoe was approxmently at 5 o'clock and right cylinder comp. TDC and it was 11 o'clock. So i guess the timing is pretty close to right.

Click to expand...

Stop playing about and check the ignition timing properly.

Triton Thrasher said:

Stop playing about and check the ignition timing properly.

Click to expand...

Tomorrow i'll dismantle AAU since thats what i suspect to be faulty. With the strobo i cannot see bike advancing at all. So the timing will be also be re-set correctly.

Contacted prewious owner and he bought this bike 2014 and he newer had done anything else than regular oil change etc service.

It feels so strange and somehow after almost 4 years it would AAU would have slipped.

If i cannot get it running like before then i'll ditch the magneto and fit Ignitech ignition.

So you have checked the ignition with a strobe lamp and it does not advance as you raise revs from idle?

That does somewhat obviously point to an auto advance that does not advance.

Triton Thrasher said:

So you have checked the ignition with a strobe lamp and it does not advance as you raise revs from idle?

That does somewhat obviously point to an auto advance that does not advance.

Click to expand...

Hello,

Yes thats correct, with strobe light you can see that its not advancing at all. Thats why i suspect AAU not working properly. I remember when i bought the bike and i was wondering why it has adjustable cam ring in the magneto (you could retard the ignition with cable, its now not in use anymore) and i checked with the strobo light back then if it had AAU and it did.

With strobe light you can clearly see that the advance kicks in when start to rev up from idle, but now its not kicking in at all.

KuusistoNorton said:

Hello,

Yes i mean the sparks when points open.

I checked timing following the tutorial/manual in the link that Slick has added,

Left cylinder compression TDC and the shoe was approxmently at 5 o'clock and right cylinder comp. TDC and it was 11 o'clock. So i guess the timing is pretty close to right.

So im curious about the blown condenser, id be pleased if someone would confirm that the points are not supposed to arc/spark? If they dont and the conderser is wasted, then i dont know if i have any other choice than pull the mag out and tear it down and replace condenser with brightspark set.

But would these be the symptoms what you could get with bad condenser?

Click to expand...

1) arcing at the points suggests the capacitor is open circuited ..... like having no capacitor at all. This will cause points to quickly pit and fail, but otherwise does not cause an engine to run as you describe. Capacitors usually become short circuited, from age and especially when hot. Shorted caps kill the engine, especially when hot.

2) you report the points block can be advanced by hand, but you see no angular movement with mag cover off and running up the engine rpm. This suggests either a) there is a fault with the bob weights, or b) the AAU is always in full advanced position.

3) installing a Bright Spark capacitor requires the cam ring housing to be removed, and the capacitor open circuited by clipping one lead. I do not recommend disturbing the cam ring housing because special tools and expertise are required to refit the cam ring housing ensuring the spindle is perfectly centered. If your capacitor is indeed open circuited, you can install a Bright Spark cap without the need to disturb the cam ring housing. You have nothing to lose but the cost of a Bright Spark cap, it should stop the arcing, but will not solve your other problem(s).

4) the rubbing shoe at 5:00 & 11:00 indicates your timing is not 360 degrees off, but does not guarantee the timing is perfectly set at 32 deg BTDC. The spoke in the hole technique should get you close enough to spec, but a degree wheel is preferred.

Next step ..... inspect bob weights. Ensure the little raised tabs are properly engaged in the slots. Move the bob weights with your fingers ..... does the mechanism rotate the armature shaft? Check that the springs are not broken or are not engaged with the respective holes in the weights and stationery part. The springs may have become weak with age and need replacing.

Also check drive chain tension .... there should be minimum 3/16 up/down movement.

Report back.

Slick