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A strange one

Points Based Ignition | Electronic Ignition Upgrade
mike in idaho
honda305.com Member
Posts: 411
Joined: Sun Jan 29, 2012 9:18 pm
Location: orofino, idaho

Post by mike in idaho » Fri Jul 20, 2018 3:19 pm

"Here's an interesting one, when running (& mis-firing) if I pull off & hold the plug-cap away from the plug, a large spark jumps the gap & it instantly picks up & starts running perfect, put it back on & it mis-fires!!"
That plug is gas-fouled, toss it and install a new one.
'65 YG1
'65 CB160
'66 CL160
'66 CL77
'78 XS650
'79 GL1000
'69 T100R
'68 TR6
'69 T120
'72 750 Commando
my company car is a Kenworth

modelman
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Posts: 222
Joined: Wed Jun 24, 2015 2:27 am
Location: Yorkshire, UK
Contact:

Post by modelman » Fri Jul 20, 2018 3:48 pm

They are new plugs.
GSX1400 Red/silver
GSX1400 Blue
GS1000G
Brockhouse Corgi
CB77
CA77
T140
BSA 250

I DO have to grow old, I DO NOT have to grow up.

mike in idaho
honda305.com Member
Posts: 411
Joined: Sun Jan 29, 2012 9:18 pm
Location: orofino, idaho

Post by mike in idaho » Fri Jul 20, 2018 5:38 pm

How long have they been in the motor? It takes literally seconds to foul one with a slug of raw gas. Try a new plug anyway(they don't cost that much).
'65 YG1
'65 CB160
'66 CL160
'66 CL77
'78 XS650
'79 GL1000
'69 T100R
'68 TR6
'69 T120
'72 750 Commando
my company car is a Kenworth

rrietman
honda305.com Member
Posts: 561
Joined: Mon Oct 13, 2008 6:45 pm
Location: bellingham wa.

Post by rrietman » Sat Jul 21, 2018 12:43 am

OK so sometimes when you are diagnosing you go thru a bunch of spark plugs, just to zero out that variable. here's an old time trick. chuck the suspect plug in a vise, get out the oxy torch and heat it red hot, the carbon will jump off and you have a good plug.
goodluck
Randy

modelman
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Posts: 222
Joined: Wed Jun 24, 2015 2:27 am
Location: Yorkshire, UK
Contact:

Post by modelman » Sat Jul 21, 2018 1:33 am

I can accept the scenario of a dud plug, I can also accept a fouled plug, but can't get my
head around the fact that it fails/mis-fires when connected, but then runs fine if the plug-cap
is pulled off & held a short distance away!

I even removed the cap & held the end of the (new) HT lead on the plug, same thing & when pulled away there is a massive 1/4" spark to the plug & it runs great.

Is it possible that a duff plug can somehow be 'induced' to fire when a ginormous spark is applied at the cap-end??? I must admit to the fact that it seems plug related.

Last night I removed the condenser ( that was fun ) & this morning i'm going to fit a replacement & we'll see if that makes a difference.
GSX1400 Red/silver
GSX1400 Blue
GS1000G
Brockhouse Corgi
CB77
CA77
T140
BSA 250

I DO have to grow old, I DO NOT have to grow up.

User avatar
G-Man
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Posts: 5678
Joined: Wed Mar 25, 2009 5:17 pm
Location: Derby, UK
Contact:

Post by G-Man » Sat Jul 21, 2018 4:40 am

Modelman

All that the long spark does is increase the voltage at the plug points. You're just storing the charge up for a bit longer to build up a more energetic spark. The biger (and more vigourous) spark jumps across the gap and hey-presto.

G
modelman wrote:I can accept the scenario of a dud plug, I can also accept a fouled plug, but can't get my
head around the fact that it fails/mis-fires when connected, but then runs fine if the plug-cap
is pulled off & held a short distance away!

I even removed the cap & held the end of the (new) HT lead on the plug, same thing & when pulled away there is a massive 1/4" spark to the plug & it runs great.

Is it possible that a duff plug can somehow be 'induced' to fire when a ginormous spark is applied at the cap-end??? I must admit to the fact that it seems plug related.

Last night I removed the condenser ( that was fun ) & this morning i'm going to fit a replacement & we'll see if that makes a difference.
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160
'66 Matchless 350 '67 CL77
'67 S90 '77 CB400F

modelman
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Posts: 222
Joined: Wed Jun 24, 2015 2:27 am
Location: Yorkshire, UK
Contact:

Post by modelman » Sat Jul 21, 2018 7:17 am

So what are you saying Graham, the plugs are dud, or another electrical problem??

I'm at my wits-end just now, fitted a brand-new condenser this morning, & have the same results, SIX new plugs, new leads new caps, tried another coil, a little video shows just whats happening, & i'm beginning to suspect the plugs as I tried a couple of old 14mm plugs & they fired/sparked just fine.
Anyone else had bad experiences with 'new' plugs?? as ALL worked for a day or two, now none do, & i'm wondering if there's a load of fakes out there.
BTW, stripped the carb again, it DOES have the voids in both spacer & carb, found the needle had a slight bend halfway so I fitted a new spare I had,(middle groove)

https://www.dropbox.com/s/c00gv661ir92a ... 3.mp4?dl=0
GSX1400 Red/silver
GSX1400 Blue
GS1000G
Brockhouse Corgi
CB77
CA77
T140
BSA 250

I DO have to grow old, I DO NOT have to grow up.

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