CD 125 not starting

[wathsa]

Hi all
I recently bought a 1991 CD 125-Platinum, The seller chocked and throttled and got it started in few tries. But i can't get it started.

The self start is broken so that the kick starting is the only way. The battery is 6v. When switched on the horn and things are not working. But after some trying with choking and kicking hardly can get started. Is that due low battery?Do you think that converting it to a 12v is good or replacing the battery is good?

Or if it is an issue with rectifier etc how to figure out? Few steps if possible please


Need your advice please
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WAT

[MCN]

Maybe a Printed Circuit Board thingy that creates the spark. (CGI ignition)
I don't know and I'm not googling for it.

It could be timing.

It could be fuel.

You will need to try the easiest checks first.

If there fuel in the tank? Lid off shake it or fill it up.
Is fuel getting into the engine? Turn the engine over and have a whiff of the exhaust pipe. Does it smell petrolley?

Then do you have a spark at the plug? You can use a spare spark plug in the plug lead and hold against the metal of the engine as you turn the engine over. Look for a big Fat Spark. If no spark then the issue is electrical and you'll need to roll your sleeves up to the armpits.

Checking the fuel system is not as easy as it makes a mess and petrol is flammable and an irritant.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Teflon-Mike]

It's a self-excited ignition. Ie the spark-plug doesn't get its electric from the battery,but from the magneto spinning around on the end of the crank.

So... your battery.. shouldn't make much odds... it will, because e-start wizzes crank-shaft over faster than the kicker, so it does make more electric for sparks.. b-u-t.

Conversion to 12v? Pros and cons. Cons is that a 1991 CD125 is almost 30 years old, its 'sort' of a classic, where the more original the better. Pro's are that 12v is the more common and you can get things like headlampbulbs!... b-u-t its no small conversion and you have to change ALL the electrical equipment for12v, that means every light bulb, the horn and importantly the starter-motor itself... on a Benley, conveniently there is a plathora of parts that are already 12v available, and getting something like a 12v starter motor that will fit isn't too big an issue... but likely a big cost, when youtally it all up.

Personally, I would probably 12v convert it. But I would be starting with a bare frame resto, which I'll go into more of in a mo, so I would be swapping out most of the electrical system and re-wiring with nice new non-corroded connectors and stuff anyway... and I have a shed load of Benley bits knocking about anyway....

Back to bare frame resto... the first thing I would be wary of on a wire-wheel Benly is those wire wheels. The rims are steel and they rot... especially after 30 years... may look OK when you polish the chrome, but they go from the inside, so I'd be looking at them with the tyres, which also rot, and probably need replacing 'off'. If the hubs are OK, then are build with new spokes and rim, is likely to set you back around £200 a wheel, and frankly on an old Benley, it's probably not worth it. Just the spokes and a new rim, are around £100 a wheel to DIY and I'm not that good a wheel builder.

Oh-Kay... that one out the way; onto the engine.

Its essentially the same engine as the CB125T, the CM125, the CD185, CD200, and the CB/CD/CM250.

The 125's all share the same common barrel and pistons and even the compression ratio, the main differences are that the CB125 has a 180 crank, one piston up and one down, where the CD and CM have a 360 crank, both pistons going up and down together; hen the CB has a twin trigger ignition to fire the spark plugs at 180 degree firing intervals,where the CD & CM have a single trigger ignition with a siamesed coil, firing both plugs at the same time, on the 'lost spark' principle where one spark is happening when needed, the other wasted in the exhaust of one that';s just gone bang.

Anyway, these engines have a tiny little 62cc cylinder, and consequently small bore. They really dont like worn bores or worn piston rings, or they dont make the compressionthey should to go 'bang', and a very small aount of wear will result in poor starting and running.

At 30 years old, good odds that the poor thing has either clocked up moon and back mileages and or spent a lot of time derelict. Iff high mile then the bores and rings are probably shot, if left derelict then odds is that the piston rings have gummed in the piston and wont seal, and more that the valve seats are rusty and the valves not sealing.

On resto, I tend to ASSUME that a top end rebuild will be required on one of these motors. See handy How2's in profile..... so I start by pulling the motor, pulling the top off it, and giving it a new chiky barel and piston kit, and reconditioning the cylinder head, lapping in the valves to get good seal between valve and seat and rennewing the likely talcum powder by now valve stem seals.

All sounds a lot scaryer than it probably is,but worth the doing to bite the bullet and tackle rather than have all the head scratching after doing everything and anything trying to avoid looking at oily bits!! (BELIEVE ME!!!)

B~U~T... to cut to the chase, that is probably where your niggle lies. An old tired motor that's long past duie an over-haul and probably needs not a new battery or coil or anything you can see,but a propper top-end rebuild.

Sorry, I know you were probably hoping for a 10p quick fix, but cutting to the chase, that's where its likely to lead you one way or another....

Meanwhile... if you really want to persevere on falorn hopes.. get the haynes; do a full and proper service; and make sure that you adjust the valve clearances and cam-chain tension... you will probably want the tappet tools, see Handy How2's for part numbers, they only cost about £15 and save sooo much hassle, and you should be needing them every 2ooo miles anyway... and yes a new battery is probably a good idea, and I really woruldn;t worry about things like the rectifier at the moment or 12v conversions.... reconditioning the starter motor with new brushes and cleaning the starter solenoid would be far higher up the to-do list.. after I was sure,having checked the wheels, tyres off, that there was any merit doing anything to 'this' particular motorcycle....
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[stinkwheel]

Genuine question, would a 6v starter work with 12v? What would the effect be?

I'd imagine it would try to turn twice as fast with half the cranking power?

On old enfields for a 12v conversion they just stick a 12v regulator on and swap the battery and bulbs. Everything else is designed to cope with double the amps they're now getting.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.