Author Topic: Stalling and rough idle  (Read 764 times)

Offline hdawson

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Stalling and rough idle
« on: 02.06. 2018 01:20 »
Hi All,
After a recent ride not far from home the BSA was wanting to stall at the lights and only constant revving would keep the engine running until I could find a safe place to park. Refusing to start I had to do another trailer recovery.
With a cool engine it seems to start as usual but idle is terrible. The tick over varies about 1K rpm and any throttle input is wild.
Plugs look good and I have a  nice blue flame through the colourtune.
I checked the timing, points gap and condition and all seems OK.
If the problem is mag related what steps should I take to eliminate the problem?
I am happy to send the mag off for a rebuild but would like to ascertain if this is necessary.
Cheers, Hadrian 


61 BSA Super Rocket (cafe).
51 Matchless G9 Clubman.
81 Suzuki GSX 750 ES.
02 Triumph Sprint.

Offline worntorn

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Re: Stalling and rough idle
« Reply #1 on: 02.06. 2018 04:50 »
I had a similar problem with my SR. An Easycap fitted to the mag fixed it.

Glen

Online Billybream

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Re: Stalling and rough idle
« Reply #2 on: 02.06. 2018 05:00 »
Sounds like your mag capacitor is the probable culpit, but not an easy fix to prove.
1960 Super Rocket, owned since 1966, back on the road 2012 after being laid up for 29yrs.

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Re: Stalling and rough idle
« Reply #3 on: 02.06. 2018 06:38 »
G'day Hadrian.
At first I thought air leak.
It would have to be ignition if the flame colour is blue. The Easycap would be a cheaper trial to fix the problem if you DIY. Brightspark have a distributor  "Australia: OK2F Magneto and Dynamo Repairs in Prospect, Adelaide, Australia." You'd be looking at $5-600 for a rebuild.
Cheers
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Online metalflake11

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Re: Stalling and rough idle
« Reply #4 on: 03.06. 2018 23:48 »
Start simple and cheap to begin with. Plugs, caps, leads. Check the pick-ups for cracks, and finally the brushes and springs.

If that fails to fix it move into the mag itself. I've had those rubber caps rust away internally after one winters riding,  I've also had leads start to break down after time too.

It's not always worse case scenario, it's often a simple thing, due to some of the tripe offered for sale these days.

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Online chaterlea25

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Re: Stalling and rough idle
« Reply #5 on: 04.06. 2018 20:49 »
Hi All,
If you fit  a colour tune or attach a strobe light, you can see if the ignition is misfiring
Bad capacitor will result in excess sparking and blackening of the contact points

John
1961 Super Rocket
1963 RGS (ongoing)

Offline hdawson

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Re: Stalling and rough idle
« Reply #6 on: 06.06. 2018 10:52 »
Thanks all for your feedback.
Tonight I did a thorough inspection of leads and clean of the pick ups and slip ring.
Started nicely and sounded good, leading to high hopes for the simple fix.
I always fall for that one!
However after a few minutes the same problem returned   *conf*
Looks like I have to remove the mag and expose the horrors that lie within  *eek*


61 BSA Super Rocket (cafe).
51 Matchless G9 Clubman.
81 Suzuki GSX 750 ES.
02 Triumph Sprint.

Online morris

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Re: Stalling and rough idle
« Reply #7 on: 06.06. 2018 21:46 »
Thanks all for your feedback.
Tonight I did a thorough inspection of leads and clean of the pick ups and slip ring.
Started nicely and sounded good, leading to high hopes for the simple fix.
I always fall for that one!
However after a few minutes the same problem returned   *conf*
Looks like I have to remove the mag and expose the horrors that lie within  *eek*
Carbon traces from to soft pick ups on the slipring?
Remove one plug cap and start it. If it runs one one cylinder and stalls the moment you put the cap back on it’s almost certainly that.
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Offline hdawson

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Re: Stalling and rough idle
« Reply #8 on: 20.06. 2018 09:35 »
Thanks Morris.
Checked that - but no stalling during the process.
I will remove the mag this weekend but what puller do I need or how do I manufacture one ?
Hopefully the Matchless type that I have may do the job.
Cheers,
Hadrian.

61 BSA Super Rocket (cafe).
51 Matchless G9 Clubman.
81 Suzuki GSX 750 ES.
02 Triumph Sprint.

Offline hdawson

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Re: Stalling and rough idle
« Reply #9 on: 20.06. 2018 10:07 »
BTW, I have read elsewhere that the Easycap is not a permanent fix.
Is this the case?

61 BSA Super Rocket (cafe).
51 Matchless G9 Clubman.
81 Suzuki GSX 750 ES.
02 Triumph Sprint.

Offline hdawson

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Re: Stalling and rough idle
« Reply #10 on: 20.06. 2018 10:34 »
More encouragement on the interweb regarding a condensectomy.
"Removing the old capacitor
Once you've spent a year getting the armature apart mark the live side with a red marker and the end of the armature so that you know how to put it back later. The positive side is the side with the insulator and connects to the capacitor where it flows through and out the centre hole to the contact breaker long screw."
 *eek*

61 BSA Super Rocket (cafe).
51 Matchless G9 Clubman.
81 Suzuki GSX 750 ES.
02 Triumph Sprint.

Offline mugwump

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Re: Stalling and rough idle
« Reply #11 on: 20.06. 2018 10:59 »
Once the mag has warmed up and giving trouble, try a spare spark plug ( with approx 1/4"  electrode gap ).
If no or poor spark that will indicate the mag is due a rebuild. A good mag should jump that gap.

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Re: Stalling and rough idle
« Reply #12 on: 20.06. 2018 17:52 »
Changing a capacitor isn't going to fix a duff coil, obviously, but it will address a defective condenser.  No surprise there.

Sometimes, replacing a duff condenser will seemingly re-invigorate a coil that is past it. Many past-it coils show no HT continuity due to a small break inside, which the spark is capable of jumping . . .  and they still deliver a passable spark at the end of the line, ie the Plug.
With a duff condenser as well as a past-it coil, the mag won't run right. With a new capacitor, of any sort, it might come back to life. But the break will get worse because there will be internal arcing in the coil.

So - the only sensible approach here, when starting to play, is to check for HT continuity as a first move. If there is none from the SLIPRING to the armature spindle ('earth'), then it MIGHT just be that the connection between the coil and the slipring is bad, and replacing the ring might restore things. But usually, it's a break in the coil and it's a false economy not to get it rewound. (Unless, of course, people have many years spare to get armatures out, and enjoy doing it.)

You'd expect to see, typically on a K2F, 5000-odd ohms from the brass part of slipring to armature spindle with everything connected. That figure might be as high as 7000 ohms on some windings, or as low as 4000 on some others, as the recipe of number of turns, wire gauges for primary and secondary etc, varies from rewinder to rewinder. (There are plenty of lower and higher numbers on other makes/models.)

Not to confuse this with LOW tension continuity  . . .  Between the base nut for the cb centre screw and the 'earth', there will only ever be about half an ohm as the winding (which lies under the HT one on the same core) has relatively few turns and is chunky. They don't fail often, in fact failure is rare as hens' teeth.

If it takes someone a year, even in jokey metaphor-speak, to get an armature out or opened up, that's probably not a good source of advice! It is actually pretty obvious which side of the low tension winding (and the condenser) is live and which is to earth, because one side is directly connected to the 'nut' on the cb centre screw via the condenser's tin case, and the earth side is attached to the armature brass end by the same tab that holds the condenser in place on a K2F (and most if not all Lucas). The earth side of the low tension winding is soldered to the said tab. Not hard to figure, and just needs eyes, or a £5 multi-meter for those who disbelieve what they see, to establish which is which.

In the event that the low tension wires are inadvertently reversed, the mag will still work. There are reasons why it's better to get it right, to do with getting the last bit of spark intensity and also the correct negative spark at the plug on singles  - but you get one of each on a twin whether you like it or not.

There are no free lunches, and it remains true as ever that it is a BAD idea to start playing with anything if you haven't sussed out what to expect! Those of us who mess with these things every day try quite hard  to explain much of this stuff, via websites, chats, face-to-face, whatever. But just as it's a bad plan to strip a gearbox, say, without taking bloody careful note of how the selectors and camplate work, which gears go on which shaft in which order, where the spacers and thrust washers etc etc go, it's a bad idea to start pulling the leccy bits apart without a care in the world. They'll come back and bite, guaranteed!
Bill

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Re: Stalling and rough idle
« Reply #13 on: 20.06. 2018 18:35 »
I love your posts Groily!

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Re: Stalling and rough idle
« Reply #14 on: 21.06. 2018 01:38 »
Hi All,
After a recent ride not far from home the BSA was wanting to stall at the lights and only constant revving would keep the engine running until I could find a safe place to park. Refusing to start I had to do another trailer recovery.
With a cool engine it seems to start as usual but idle is terrible. The tick over varies about 1K rpm and any throttle input is wild.
Plugs look good and I have a  nice blue flame through the colourtune.
I checked the timing, points gap and condition and all seems OK.
If the problem is mag related what steps should I take to eliminate the problem?
I am happy to send the mag off for a rebuild but would like to ascertain if this is necessary.
Cheers, Hadrian

It does sound like an ignition problem, but the symptoms are also similar to those of a worn carb slide, or a carb getting too hot (no fibre spacer?)......or as posted above an air leak between carb and head, it might be worth checking these out before going an expensive mag refurb route.
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