Author Topic: No sparks at 3MPH  (Read 349 times)

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Offline tck

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No sparks at 3MPH
« on: 10 Jun 2021 at 10:14 »
On my Mk3 I have had the mag rebuilt and after getting no sparks I took it back again and I have seen it sparking at low revs on the test rig (yes correct rotation!) after fitting it back for the second time and timing it yet again
I load the bike on my mains rollers and at 3MPH on the speedo in top on one occasion I got a slight discharge at the edge of one  plug  on one occasion but nothing on the other.attempts, Of course the bike newly rebuilt will not run at all not even a backfire advancing and retarding no affect
Mag tested with leads and plug caps
plug caps non suppressed rubber
timed at 36deg tight wire
mag pick up brass band in evidence on side being timed
all new carbon pickups
tried NGK new B6HS & B7HS  bought from green spark plug company not ebay
Does anyone know if resistance between mag body holding studs and head is ever a problem?

will I ever get this going? suggestions welcome

Offline eddie

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Re: No sparks at 3MPH
« Reply #1 on: 10 Jun 2021 at 10:28 »
When the mag was run on the test rig, I guess there was no cutout in circuit - so try again with the cutout wire disconnected. If you then get a spark, have a look at the cutout button - maybe the grub screw that secures the wire is shorting to the handlebars.

  Eddie.
« Last Edit: 10 Jun 2021 at 10:35 by eddie »

Offline tck

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Re: No sparks at 3MPH
« Reply #2 on: 10 Jun 2021 at 10:54 »
Thanks eddie, I took the cut out  cap off earlier, and continuing the take it off theme and try  I now have the rubber 'racing' caps off and a wood screw in each and the lead in the fins now  I get an occasional spark but certainly not at the speed the engine is turning but worth trying further. Back in the day I would pinch the hooks from the ends of mums half net curtain springs  the bike would run and she would wonder why the B&W TV had interference and her curtains were missing  :P

Offline dalgrae

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Re: No sparks at 3MPH
« Reply #3 on: 10 Jun 2021 at 12:11 »
Hi are B6hs plugs surpressed ,I always run non surpressed plugs as well as caps

Colin

Offline eddie

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Re: No sparks at 3MPH
« Reply #4 on: 10 Jun 2021 at 12:21 »
Tim,
        You also mentioned 'new carbon pickups' - was this just the carbons or bodies as well? I have heard that some of the repro pickups are a bit suspect - if you still have the old pickups, try putting them back in (in case the spark is tracking across the new pickups). Also, try shortening the central points retaining screw by about 30 thou, in case it is long enough to short out to the main windings.

  Eddie.

Offline tck

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Re: No sparks at 3MPH
« Reply #5 on: 10 Jun 2021 at 13:02 »
I checked the pickups no sign of tracking I dont have the originals at least with no caps just a wired connection I get some sparking on one side now  I did try to start it again but only got a fitful rumble on the spark side at full retard full choke and shut throttle it would not pick up.  I will now  swap over the lead and plugs

Offline eddie

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Re: No sparks at 3MPH
« Reply #6 on: 10 Jun 2021 at 14:26 »
Tim,
       With the pickups removed, turn the mag until the points are about to open, then operate the advance/retard, and check that the brass segment of the slip ring can still be seen for all positions of the advance/retard. If the brass segment goes out of sight, the armature has probably been fitted with the wrong hand slip ring.

  Eddie.

Offline tck

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Re: No sparks at 3MPH
« Reply #7 on: 10 Jun 2021 at 15:13 »
Yes brass seg is there in both points opening advance & retard position on the no spark side tappets loose so on right stroke check points open to TDC 7.1mm

Offline Paul H

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Re: No sparks at 3MPH
« Reply #8 on: 11 Jun 2021 at 03:54 »
Hi Tim,
At 3mph in top gear the magneto is probably not spinning fast enough to generate a spark. Try a lower gear.
Paul.

Offline EW-Ron

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Re: No sparks at 3MPH
« Reply #9 on: 11 Jun 2021 at 04:01 »
Also some mags will not spark when fully retarded.
Try half retarded ?  Or fully advanced ...

If you can't get a spark from using the kickstarter when the plugs are out, somefink is wrong.
As you have deduced by now !

What happens when you spin the maggie by hand.
My EIC gives lovely blue sparks...

Offline tck

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Re: No sparks at 3MPH
« Reply #10 on: 11 Jun 2021 at 07:00 »
This is a brand new engine I doubt that the shock absorber or tyre to roller would take turning over in third top is certainly faster than any kick I would think certainly it ignights most bikes I roll on there

Offline phil1

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Re: No sparks at 3MPH
« Reply #11 on: 15 Jun 2021 at 06:51 »
Hi Tim
             Think I might try swopping the plug leads over, and cross your fingers. Phil.

Offline eddie

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Re: No sparks at 3MPH
« Reply #12 on: 15 Jun 2021 at 07:23 »
Tim,
        Try starting it in 2nd gear on the rollers. Get the rear wheel spinning - don't feed the clutch in, drop it like it was red hot - the inertia of the rear wheel should bump the engine over a couple of compressions. My 600 sprinter, on a 10:1 CR, starts easily like that.

Regards,
               Eddie.

Offline tck

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Re: No sparks at 3MPH
« Reply #13 on: 15 Jun 2021 at 08:06 »
Thanks for you kind suggestions
I have it back on the workbench rechecking everything I have to re secure the exhausts more securely and fit some new spark plugs then try again

 

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