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Head Troubles (mine)
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Swing42
NSW Australia
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November 15, 2020 - 8:31 am
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Just cannot get this bike to run properly .. 1956 D3 ..

We've rebuilt the engine withe new parts,seals etc,fitted a whizz-bang CDI ignition,renewed carburettor parts,timed it correctly,jetted the carb ... everything that a restoration usually entails  ..

It'll now revv like a chainsaw ,if its in neutral,but when riding,it wouldn't pull the skin off a rice custard 🙁 ..

Loosening the 3 screws on the stator plate and rotating it when the engine is running at about 1/4 throttle didn't seem to make any difference. 

So,I'm asking .... will the engine run AT ALL ... with the piston in backwards ? (we're sure we got that right .. or did we ?) 

Thanks all .... 

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Number6
Lincolnshire
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November 16, 2020 - 12:14 am
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If the piston was backwards the ends of the rings would snag in the ports and break off, I think, then you'd know all about it.

Personally I'd forget the CDI for the mo as a "step too far" and try to get it working on points, the old original system. Summat is awry alright. cry

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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Number6
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November 16, 2020 - 12:22 am
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Loosening the 3 screws on the stator plate and rotating it when the engine is running at about 1/4 throttle didn't seem to make any difference.

From memory, it doesn't work quite like that, you ride it to see what it's like, if you want to try tweaking the timing stop, alter the angle a bit, ride it some more, if it behaves better OK, if it behaves worse, stop again, put it back where it was, and like that. Owner's manual says once set right it shouldn't need altering on a regular basis, which makes sense if the contact breaker gap is kept correct.

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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cocorico
Central France
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November 16, 2020 - 7:36 am
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Swing42 said
Just cannot get this bike to run properly .. 1956 D3 ...

It'll now revv like a chainsaw ,if its in neutral,but when riding,it wouldn't pull the skin off a rice custard 🙁 ..

... will the engine run AT ALL ... with the piston in backwards ? ...

As No6 says, piston backwards runs the risk of ring breakage, but I don't think it will affect running 'per se'.

If it revs in neutral, is that uncontrolled revs or on the throttle? As for the power, I'm not sure of the consistency of Ozzie rice custard skins, but a D3 is not over endowed with horses anyway - do you mean it bogs down when in gear, or some other description?

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Swing42
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November 16, 2020 - 8:57 am
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An update ...

First of all ,thanks heaps for your responses... greatly appreciated..

Ok.. the piston is not in backwards ..good.

I've already bought the CDI,so the one which was lent to me will be going back.They got good reviews here ,so that's the way we went.

Now to the power issue .... I spoke to Bones ,designer of the CDI unit and owner of OZ Bantams today, and I think he's worked out what the problem is... power (the Bikes') to weight (mine) ratio ...

" a D3 is not over endowed with horses anyway" .. me being a reasonably rotund sort of a chap at 92 Kgs,riding a 150cc Motorcycle was expecting too much from his machine ...

.. And what made things even worserer 😉 ... was the fact that we fitted a 16 tooth gearbox sprocket.We live in rural Australia and as I thought that all the riding to be done would be done on the highway,the 16 toother would make for a lower revving ride.Seems as the donk is not powerful enough to cope...

We've ordered a 15 tooth sprocket and are hoping for a good result .. progress report to follow.

What do you think about this ? does it all make sense as a diagnosis ?

Thanks gents ...

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cocorico
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November 16, 2020 - 9:21 am
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Well, I have a '56 D3 too, which is on standard gearing and fairly flat rural roads. She is happy at around 40mph and I am about 86kg, so a bit more streamlined. In comparison, I have a 125cc Honda Pantheon scooter which blows the D3 into the weeds...

However, here's a short clip of the D3 on a hill...

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Swing42
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November 16, 2020 - 9:30 am
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Cheers Coco .... do you have a 15 tooth sprocket fitted ?

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Swing42
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November 16, 2020 - 9:32 am
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Is a 15 tooth sprocket standard gearing ? ... my rear sprocket is 47 tooth ..

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Sponge
Lancashire (A chip shop somewhere near Preston)
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November 16, 2020 - 11:24 am
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Swing42 said
Is a 15 tooth sprocket standard gearing ? ... my rear sprocket is 47 tooth ..  

Mate I weigh about 155kgs and ride a D1 with a Bones ignition. Set up properly it goes OK so I wouldnt be too worried about yr weight.  15/47 T sprox is a good set up on roads through rolling countryside but if it truely dies when you open the taps I would suspect it, has a blockage,  needs a decoke or has an air leak. 

Hope you get it sorted soon. Songs 

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cocorico
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November 16, 2020 - 11:32 am
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I think mine is 15/47, but it's a few years since rebuild...

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Number6
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November 16, 2020 - 2:46 pm
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I tried a 16 tooth on my D3, I think was the only reason was couldn't get a 15 tooth; was OK on the flat, could get an indicated 55 mph flat out if no wind or gradient (but need to factor in possible speedo error, and it wasn't the OEM Smiths 'D' shape one, I'd lost that somehow, altho it came to light much later, so I was using a round one like the later models have?)

However steep hill or into a strong headwind, utterly feeble, couldn't pull third, aka couldn't get it out of second. Engine was top notch too had had a rebore, new piston and rings, completely rebuilt, new bearings etc., rebuilt crank and everything, however also need to bear in mind even a 100% fit D3 is still only 4.9 bhp.

I was only about 9 stone at the time as well, what's that 60 kg? Or a bit less.

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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Number6
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November 16, 2020 - 2:52 pm
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Swing42 said
Is a 15 tooth sprocket standard gearing ? ... my rear sprocket is 47 tooth ..  

Yes for both.

What I found, putting a 16 on the front made the gap between 2nd and 3rd even more hugerer ... freaked-out_gif

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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GlenAnderson
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November 16, 2020 - 3:04 pm
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16 tooth front sprocket is definitely too big. They can barely pull the 15. 

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Swing42
NSW Australia
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November 16, 2020 - 10:58 pm
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Cheers Amigos ... a 15 tooth sprocket is on it's way to me ... progress report to follow.

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