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Misbehaving D7
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stubaker58
Sunny Felixstowe
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February 2, 2020 - 11:11 pm
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OK, so my D7 mongrel was going perfectly well until my return journey from the National Rally last year. On the way home it started to misfire a bit and wouldn’t rev out.

When I checked the gennie was loose with a screw missing, so I replaced the screw, reset the points & timing and ... no difference.  Next stop was to clean out the carb, plenty of muck in the banjo filter (despite an in line filter), cleaned it out, replaced the idle jet made sure everything was clean ... no difference.

The bike starts well enough and pulls away but tops out at around 40 and lacks any urge, it seems to ‘flutter’ on full throttle and maybe worse once it’s properly warm.  It soldiers on but has lost any pep.

So what next? I’m thinking change the condenser, then the coil and then give the exhaust a roasting with the hot air gun but any suggestions gratefully received.

(BTW it’s still 6v, separate coil ignition with a battery and points)

regards.

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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Blue Heeler
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February 2, 2020 - 11:44 pm
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Got to be linked to the gennie working loose....unless one hell of a coincidence eh?

Shame you`re not closer, I`d just strip out that left side and replace with parts from one of my spare motors. Anyone down there with some spares they`d loan you?

Maybe shorting or other damage from being loose. Maybe a condenser like you suggested, they can give those symptoms. A cheap easy thing to try first.

I would try running her in the dark, looking for rogue tracking...extraneous sparks. That approach has revealed stuff in the past for me. My heart can also tolerate the touchy-feely-jumpy approach to handling HT leads, plug caps, but I`ll never touch a coil. Disclaimer:In case anyone`s getting ideas reading this, please don`t do this with electronic ign or with any systems if you have heart issues/pacemaker etc.

I`ve had HT leads, plug caps, condensers go...even faulty plugs. Had one of the ignition coils on my `76 LeMans causing a misfire.

Something is shorting out surely. Check all earths too.

...or it`s not something simple like the throttle slide needle working loose, or throttle cable adjuster slackening itself?

Blue

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bantammad
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February 3, 2020 - 11:01 am
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Hi bantammad ere just a suggestion you need to have a small battery pack make up to 6v dry type. 6v coil. Two lengths of wire Ht lead , basically independent ignition supply follow me. May help to find out your faults. This way you will be able to test ride the little beast happy days LES 

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stubaker58
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February 3, 2020 - 9:05 pm
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Thanks guys.

Ive swapped the condenser, still starts well but not been out yet to check any improvement.  With the lights off in the garage the points do spark a bit. Managed to find my replacement coil so I’ll get that fitted soon. Before that though I’m going to go through setting up the points and checking the timing (again).

regards

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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chickensoup
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February 3, 2020 - 9:34 pm
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Hi there,

Had a similar problem on my D7, as it wouldn't rev out ( like it had a rev limiter ) replaced the center bronze bush in the gennie mag and that sorted the problem.

Nick.

1950 BSA D1 Plunger   242 UYW

1966 BSA D7  LBF 62 D

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stubaker58
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February 4, 2020 - 10:37 am
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Thanks Nick,

that’s well worth a try, I’ve just put in an order for one from Rex (plus a spare!).  The gennie was actually NOS and hasn’t done that many miles but being loose may have worn the bush oval.  I’ll check it out when the replacement arrives.

Regards.

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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d.nalor
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February 7, 2020 - 12:43 pm
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Have you looked to make sure that the contact breaker pivot is not wobbling about.

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stubaker58
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February 7, 2020 - 2:48 pm
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I’ll be out there first thing having a good look at the generator side, new bush at the ready.

ill let you know how I get on.

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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stubaker58
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February 8, 2020 - 1:46 pm
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Latest update.

I spent an enjoyable morning going through the points, timing, dismantling and checking over the generator, checking the bush etc. I made up a drift for the bush and used an old spark plug drilled out with a rod down the central plug head to measure 1/8th BTDC. I filed smooth the slots in the stator and fitted new washers.  Put it all back together with the original condenser (new one on its way).

Started first kick and revved well, no sparking at the points, out for a spin .... no better!

This time though I noticed that when warmed up a bit it seemed to pick up when I closed the throttle slightly.  I’ve been looking for an electrical fault because of the loose stator plate but maybe it’s carburation?

All help gratefully received!

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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Blue Heeler
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February 8, 2020 - 3:54 pm
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Yes, maybe carb needs a strip and clean or petrol tank filler cap breather blocked...but you still can`t rule out the condenser, because that behaviour is similar to one of the faulty condenser symptoms. Watch out for faulty new condensers, there was a batch not long back.....reported on here.

Has your throttle slide needle worked out of its clip? Sort of fits revving ok on the stand, but no pick up on the road.

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