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#648129 - 04/11/16 2:56 am Random misfire - I'm out of ideas 1970 T100c  
Joined: Feb 2006
Posts: 635
Ginge Offline
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Ginge  Offline
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Posts: 635
Qld, Aust and Otago,NZ
I have been chasing a misfire on my bike for six weeks. It's a standard T100c, single AMAL 626 carb, with Daytona style pipes. It's been rewired by me and has a Sparks alternator, solid state reg/rec and Trispark ignition. Two 6v coils in series.

Bike has run well as above for four or more years. It's a daily rider so I know it's habits quite well. Riding to work it started back firing and missing. Turning the headlight off improved it but eventually it would die. If left for ten minutes it would recover enough for me to get home. I replaced the battery, even though the old battery seemed fine. Had 12.8v resting voltage and would keep the headlamp burning (engine off) for at least 15mins without dimming.

New battery has improved the bike a bit but the miss is still there. Occurs at between half and three quarter throttle. Usually as I come out of third gear into fourth and hit the 60mph mark. If I change down and increase revs I can make it go away. Bike idles fine and runs ok at low speeds.

Seems I can ride through the stumble sometimes but I also went on a 600km trip with the old battery and it never gave trouble.

I've checked everything. Bypassed ignition switch, swapped to new plug leads, new plugs, cleaned carb twice, rewired anything suspect, replaced a fuse holder. Checked tappets twice, checked carb air leaks, changed air filter. Checked timing with a strobe etc

It's better with the new battery but not fixed. I'm at my wits end.

Any thoughts?

Compression was low (110 psi ) when I last checked it. I don't thrash the bike but I don't lug the engine either


Ginge
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#648135 - 04/11/16 5:27 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
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Stuart Online content
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Stuart  Online Content
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Scotland
Hi Ginge,

Originally Posted By Ginge
Occurs at between half and three quarter throttle. Usually as I come out of third gear into fourth and hit the 60mph mark. If I change down and increase revs I can make it go away.

Hmmm ... vibe-induced? Have you tried holding it at the same rpm in different gears, marked the twistgrip and tried holding it at the same twistgrip position in different gears?

Have you tried supplying the Tri-Spark directly from the battery, bypassing all the bike's wiring and switchgear? That'll at least limit the problem to either the bike's wiring and switchgear or the Tri-Spark's wiring.

Type of fuse and holder, original cylindrical or modern blade?

How about swapping coils for known-good ones? If the bike has the standard '70 coils mounting, there isn't any vibration protection frown and - risking stating the bleeding obvious - bear in mind that, if one coil's LT has a problem, it'll cause both to misfire. frown Also, have you dismantled the coils' wiring connections to check for any looseness, especially the threaded pillars into the coils?

Did you wire the Tri-Spark according to Steve's instructions? If so, fwiw, I don't share Steve's confidence in the connection between the Tri-Spark and the 'points' pillar bolt; I extend that wire out of the engine alongside the other two to whichever is the battery 'earth' terminal.

As you're in the same country, have you tried running the problem past Steve? He might lend you another unit, to ensure the problem isn't within the unit itself?

Hth.

Regards,

#648145 - 04/11/16 6:49 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Feb 2006
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Ginge Offline
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Ginge  Offline
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Qld, Aust and Otago,NZ
All great thoughts Stuart. That's what I was looking for. A fresh brain.

Thanks mate.

I'm confident it's not vibration. I think it is poor combustion under dynamic cylinder pressure. Weak spark most likely. Runs okay under light load, not so well when pushed.

Yes it does misfire at the same throttle opening in third, but not second or first gear. Misfire in third gear is less often and less vigorous than fourth.

I never thought about one bad coil passing to the other one in series. Not sure how I can check that without buying another coil. I might try changing the Tri Spark feed and earth first and go from there.

Regards


Ginge
#648153 - 04/11/16 8:23 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Sep 2011
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Excalibur Offline
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Excalibur  Offline
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New Zealand
Some thoughts..
Tank cap breather?
Swap in another pair of known good coils?
Try it without the air filter?
Has carb had a new needle jet in recent memory?
Perhaps temp fit one of those cheap Chinese LCD volt meters to handlebar. Wire it to feed wire at Trispark/Ignition.

#648166 - 04/11/16 9:13 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Nov 2005
Posts: 7,222
JubeePrince Online content
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JubeePrince  Online Content

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Back on the mainland!
Originally Posted By Ginge

I never thought about one bad coil passing to the other one in series. Not sure how I can check that without buying another coil.


"I think it is poor combustion under dynamic cylinder pressure."

I agree.

http://www.tioc.org/boyer/boyercoildata.htm

Steve

Last edited by JubeePrince; 04/11/16 9:15 am.

'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
#648219 - 04/11/16 2:47 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Feb 2006
Posts: 635
Ginge Offline
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Ginge  Offline
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Qld, Aust and Otago,NZ
Thanks Steve, that's going to be really helpful.

Excalibur, I have checked the tank breather and replaced the needle jet. The air filter is new and the bike ran fine on that jet and filter combination. If it was fuel I don't think the bike would die completely and so suddenly. I think it would try and keep running, however roughly.


Ginge
#648233 - 04/11/16 4:34 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Jan 2009
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Dr. Z Offline
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Dr. Z  Offline
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Montana, USA
Gringe,

I had a random misfire on my T100 with a Boyer ignition and checked everything you listed. Finally I replaced the new Asian 6 volt coils with the 50 year old Lucas coils and the misfire was gone. The Lucas coils are still in use after 3 years.


Craig Zaspel

T100R
BSA A10
#648258 - 04/11/16 7:24 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Aug 2001
Posts: 742
Dave M Offline
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Dave M  Offline
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USA
Identical symptoms on my Bonneville with new Boyer, new Tympanium voltage regulator and new 6 volt coils. I too tried the measures you've described, none made a differance.
John Healy has stated that 38 degrees is too advanced, at least for a Boyer, and this jived with a post by Lannis RE an approach to timing he has adopted. This worked well on my bike and may be worth a try.

Set the timing @ 28 degrees and ride. Now very slightly advance the timing plate repeatedly over several rides under load in 3rd @ 2500, 3000 rpm range until the point of pinking. This is the spot you seek.
Now retard timing very slightly and check using strobe.
HTH






.


66 TR6R Trophy
67 T120R Bonneville
68 BMW R60/US
69 T100R Daytona

#648265 - 04/11/16 8:40 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Dave M]  
Joined: Sep 2013
Posts: 1,583
quinten Online content
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quinten  Online Content
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Pacific northwest

Coils or ...

a power supply problem . .
Maybe not the battery , but what's actually making it
To the ignition.

Key switches and kill swithes can still work ,
but limit the current
That makes it through the wire .

Check the voltage at the tri-spark unit .
Or ... better still
... use a simple visual resistance load ... (a brake light)

Wired in parallel , close to the tri-spark unit .
If the wire closest to the ignition box won't light a brake Light ,
it won't run an ignition-box and coils either .

If the light , lights , Go for a ride , if the light fickers when the engine cuts out ,
you have an intermittent short somewhere , up-stream of the bulb ,
in the
Ignition supply wiring .

.

#648269 - 04/11/16 9:29 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Mar 2005
Posts: 9,967
John Healy Online content
John Healy  Online Content



Joined: Mar 2005
Posts: 9,967
Boston, Massachusetts
Quote:
The new new battery seemed to have helped with the feeling of missing a cylinder at high rpms.


Sounds like you have a charging problem. Measure the battery voltage at 3,000 rpm. You should be seeing 14.2 - 14.4 volts.


#648296 - 04/12/16 5:09 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: John Healy]  
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Posts: 635
Ginge Offline
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Ginge  Offline
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Qld, Aust and Otago,NZ
Not sure who you're quoting there John. All good.

I've got 14.75 v and 1.2 amps charging. I thought that was a bit higher than normal but shouldn't cause the problem I'm seeing.

I'll start with voltage at the Trispark and check coil resistances.

Cheers


Ginge
#648297 - 04/12/16 5:27 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: May 2007
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R Moulding Online content
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R Moulding  Online Content
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Christchurch NZ

Ginge, my Trispark equipped TR6 developed a similar miss. It eventually left me pushing the bike through Christchurch. Turned out to be a problem with the ammeter. Bypassed it and all was good again.

Rod

#648473 - 04/13/16 6:37 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
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Dibnah Online content
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I've used Laser 2780 HT lead ignition spark testers to easily check if the spark is reaching the HT leads. Probably can't see it when riding in sunlight though.

#648489 - 04/13/16 8:20 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Oct 2006
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Pete J 77T140 Offline
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Pete J 77T140  Offline
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Stow, MA
here's a long shot - but it happened to my bike - check the tightness of the nuts which hold the tabs on the coils - mine had come loose - causing intermittent power outages.

In my case it was unexplained loss of spark totally that was the symptom, and then it would mysteriously return.


I discovered the problem as I was hooking up my new replacement ignition, which it turns out I probably did not need.

#648543 - 04/13/16 2:56 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Feb 2006
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Ginge Offline
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Ginge  Offline
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Qld, Aust and Otago,NZ
I checked coil resistances. These are Cycle Craft 6v coils which I think are Taiwanese. My multimeter has a 1 ohm resistance across the probes. Primary resistances (discounting the meters resistance) were 2.0 and 2.1 ohms. Secondary resistances were 7000ohm.
Those readings should be close enough, although I will try and get the coils checked under load somehow.

I also checked voltage at the Trispark being 12.77v.

These readings were taken in the garage. I'll try and monitor Trispark voltage on a ride somewhere.

I'll check the various fastenings and fittings again too.


Ginge
#648635 - 04/14/16 11:26 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Jun 2011
Posts: 46
Kram Ninerlum Offline
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Kram Ninerlum  Offline
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Toronto, Ontario
here are my thoughts...
1. Loose zener diode...could cause misfiring if it has an intermittant ground
2. Loose wire that goes in/out of the ammeter. My TR6R quit one day, and it took me an age to find out why...

Sounds electrical...

Last edited by Kram Ninerlum; 04/14/16 11:27 am.

1958 DBD34
1970 TR6R
1970 A65L
1975 Z1
1982 KZ1000
2004 R1150RT
1990 Beta Zero
1960 TriBsa Project
#648668 - 04/14/16 7:11 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
Joined: Nov 2004
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az-idea Offline
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palo alto,ca.
For many years I've been using E.I..both Boyer and Pazon brands
and I certainly recognize the symptom Your describing…
A failing Battery can cause it..Not that ,then
there's an intermittent short somewhere
which is also sometimes vibration sensitive..Check every connector
A particular point of sensitivity tho.. is the Trigger plate itself ..
The Bullet type connectors [trash] that feel tight..but aren't [ replace with Spade type]
[ Also The wires in the 'tunnel' that hide a break under the insulation ?]
or possibly the solder points under the trigger coils are vibration cracked
Sometimes a solder remelt/reset works ..sometimes not
I have a Box of these that were finally discarded…
Ive had better Life Expectancy with these tho
since mounting a thin [ inner tube] 'gasket' under the plate which dampens
the vibration transfer from the engine..
….Good luck…
Some intermittent Shorts are just Devilishly hard to find
But You should focus on the Trigger Plate especially too..

#648964 - 04/17/16 10:30 am Re: Random misfire - I'm out of ideas 1970 T100c [Re: Ginge]  
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John Alexander Offline
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John Alexander  Offline
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just a long shot,with all the advice you have been given a points condenser condenser has not been mentioned, worth a try.
Goldie John.

#648988 - 04/17/16 1:12 pm Re: Random misfire - I'm out of ideas 1970 T100c [Re: John Alexander]  
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Stuart Online content
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Stuart  Online Content
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Scotland
Hi John,

Originally Posted By John Alexander
a points condenser condenser has not been mentioned,

Originally Posted By Ginge
Trispark ignition.

Trispark is electronic ignition - no points, no condensers.

Hth.

Regards,


Moderated by  John Healy 


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