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Moby dicking around

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WD Forte
World Chat Champion



Joined: 17 Jun 2010
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PostPosted: 22:37 - 18 May 2018    Post subject: Moby dicking around Reply with quote

This week i are mostly been playin with this 1975 mobylette
for a pal of one of my lads

https://i.imgur.com/CCgJdst.jpg
After installing a new front inner tube
I whipped the side panel things off and found the fuel hose had been rubbing against the
pulley,hence the fuel leak.
I've now fitted a new LH outlet tap and new hose


https://i.imgur.com/GkVEcNt.jpg

Checking the 6v lectrics i find all manner of shite
wtf?
BTW that's a 12V 21/5W tail light bulb in there

https://imgur.com/SBRPu4B.jpg

Looks like the PO didn't know not all plastics can be thermo welded
I've used kwik weld to patch it up as best i can

https://imgur.com/FNidkbR.jpg

Does it need a red or pink power band?

https://imgur.com/ATuoMe3.jpg

I cant find a zener so assume the 6V AC is unregulated on these?
its blown the 12v bulbs the PO had installed though

It starts easily enough but I'm currently struggling to get the tick over down
and sorting the dodgy wiring and switches

I've be scouring the web for manuals info and stuff
and buying various bits and bobs for it
It's a very simple thing but any tips appreciated
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bypass2
Trackday Trickster



Joined: 12 Sep 2013
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PostPosted: 23:28 - 18 May 2018    Post subject: Reply with quote

are all the cables routed correctly. or to tight or sticking. is the slide sticking or the choke or the cable sticking. if you take the top of the carb of and see if the cables work allright.iddle screw in to much. as it been in regular use if not the clutch maybe sticking next time you start it is the back wheel spinning round without any throttle
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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 00:04 - 19 May 2018    Post subject: Reply with quote

6v systems gnerally don't do fully rectified, typically they just hav a diode to keep voltage in one diection.
Edit: Yes there should be a zener somewhere.
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bypass2
Trackday Trickster



Joined: 12 Sep 2013
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PostPosted: 00:32 - 19 May 2018    Post subject: Reply with quote

the mobys with the 6v only system had zener diodes. the later mobys with the12v did not have them.
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MCN
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PostPosted: 07:22 - 19 May 2018    Post subject: Reply with quote

Cool.. and just in time to get its tits absolutely ragged off going flat-oot around a field by all and sundry at the 2018 BCF Hog Roast (maybe no hog but there will be a few pigs.)

Nice one Thumbs Up
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 09:52 - 19 May 2018    Post subject: Reply with quote

Almost certainly unregulated and diode rectified.

Mrs stinkwheels YB100 was the same setup, I fitted a CG125 6V reg rec on the DC side.

Obviously this will take a degree if head scratching and referring to the CG125 wiring diagram to see where to put the wires.

Also a 6V AC regulator on the lighting side.

No more blown bulbs and reliable battery charging.

Incidentally, you can use LED bulbs designed for negative earth on the AC side BUT not the "twin filament" type, they are too efficient and you wont notice any difference in brightness between the stop and the tail.
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Rogerborg
nimbA



Joined: 26 Oct 2010
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PostPosted: 09:55 - 19 May 2018    Post subject: Re: Moby dicking around Reply with quote

WD Forte wrote:
fuel leak

Not tested for in the MOT that it doesn't need because old vehicles are so well maintained.

Don't tell The Man, we're just after getting a 40 year rolling exemption. Shhh!
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WD Forte
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Joined: 17 Jun 2010
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PostPosted: 17:53 - 19 May 2018    Post subject: Reply with quote

Currently have the carb off again to see why its ticking over so damn fast
and hopefully rectify that.
I saw a guy start one on youtube and can see how this one is running way too fast.
If I took it off the stand it would try and run away.

Speaking of rectify, I have cunning plan to do some barnyard electronics
and use half of a 20A bridge rectifier to clip the AC and see what I get.
New 'classic' light/horn switch in its way as old one fubar.
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bypass2
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Joined: 12 Sep 2013
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PostPosted: 00:11 - 20 May 2018    Post subject: Reply with quote

if the clutch is sticking it will try and run away mine did when i first got it and to release it i started it up reved it pulled the back brake in and keep it running by just a little revs it. sorted mine. also take the filter of and look were the slide is seated to high
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mentalboy
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Joined: 05 May 2012
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PostPosted: 03:52 - 20 May 2018    Post subject: Reply with quote

Damn, that takes me back. Identical to my first bike, think it was the same year too. Highsiding it on Dartmoor was quite possibly one of my most embarassing biking moments ever...


You could have got the poor lad a FS1E or SS50.
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WD Forte
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PostPosted: 15:40 - 20 May 2018    Post subject: Reply with quote

After some fiddling with poorly set cables and stuff last night
its now running at a more reasonable tickover and the variator
not/hardly engaging at throttle off.
It could do with some fine tuning I expect ( can you fine tune a moby?)
but sod it that'll do for now.

The guy came round to see it yesterday and I tried to explain how shite the 6v lights were and the technology well advanced when the Luftwaffe was bombing the shit out of Britain.
He was surprisingly resistant to my adding some regulation + led lights suggestion wanting to 'keep it original' FFS

Balls, I'll look into it anyway, he'd probably never notice if I tuck all the components out of sight.
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WD Forte
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PostPosted: 00:52 - 24 May 2018    Post subject: Reply with quote

Whilst reading up on Mobys on the interweb I got kind of interested
in the notoriously crap lights and wondered if I could improve this one.
One source said if he used the horn, the lights went out and some models had
the ignition source coil supplying the horn so to using the horn could stop the engine!


It's now turned into a kind of show and tell but
others may have old 6vAC bikes and find this useful.

First I wanted to know what I had to play with and as online info varied so much
I decided to look for myself so started at the stator plate.

The red coil is for ignition and the blue lights/horn
green dots where each coil is grounded
blue and red show the coil outputs
The flywheel has 4 magnets.

https://imgur.com/Df1ke4c.jpg

Next I had a look at the output waveform at tickover.
No load, its about 40V peak to peak (Yellow trace)
I used a 6A diode to half wave rectify it ( Blue trace)
and moved it a bit for clarity.

https://imgur.com/9UwnXNa.jpg

Next image showing the pulse frequency rising with rpm but voltage pretty stable.

https://imgur.com/t0PFhRN.jpg

So, 21v pulses eh?

Hmmmm,what to do with that?

thinks

I go into my mind palace for inspiration but all that's there are pics of
healthy young ladies playing naked tennis in slow motion

Anyway, enough tennis for now

I already have that big ass 6A rectifer diode so
I used a 7.5V zener diode and 8amp 60W rated npn transistor and various bits and build
an impromptu regulator on vero board.
After powering it up, the scope trace shows a fairly smooth 7.5vDC at all speeds
that'll do.


https://imgur.com/rsHAZFB.jpg


The 6v leds take a fraction of the power of equivalent output incandescent bulbs
3W against 26W

The larger led lit up nicely at tickover and got slightly brighter at higher speeds.
The transistor is acting like a variable resistor and as it started to warm up, I added a heatsink
and some potting

Here it is with the old and new blubs with their comparative current and wattage.

https://imgur.com/vIJl0lF.jpg


I could improve, compact or at least tidy the design but all I wanted to do was put some
working and reliable lights on this wee thing and drag it kicking and screaming into the 1950's
When the new switch arrives I'll finalise the wiring and give it some longer real world testing.
If it dont burst into flames, I'll call it a success.

The horn I'll leave as AC powered for now as I hope it will give an age related piss poor squawk.
reminiscent of flairs, Ford Cortinas and other 1970s crap






















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