Honda cd200 engine into cm125

[Slimmy]

Hi,
I have whacked a cd200 Benly engine into my cm125 to get a bit more power, however I have encountered a problem.

When the engine is started it ticks over ok but when Revved a bit it revs high on its own and sticks, revs come down but takes about 10 seconds, runs like a bag of shite.

What am I doing wrong?

The engine I’ve put in was 6v and my cm125 is 12v so I used the stator and all its 12v casing from the cm125 and added to the cd200, all fitted nicely but is this causing my issue, is that stator setup wrong some how for the cd200 engine?

I’ve cleaned carb, set up mixture screws, tried different float heights, my plugs are sooted up bad, not wet oily but fluffy carbon sooted up which wipes of easy, the cd200 engine has lowish miles and looks in good nick with good compression

If anyone can give me some advice I would be grateful
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Slimmy

[A100man]

A sooty plug is an indicator of a rich (too much fuel) issue. You need to sort this out first as it may be part of the cause of your 'hanging idle'

I take it you are using the cd200 carb(s). If so have you checked the jet sizes? Hows the airfilter looking?
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Fizzer Thou]

Did you fit the 6v coil?

It sounds as though there is a very weak spark which is just about firing the mixture but is not strong enough for full combustion.

When the engine is warm,can you do a compression check?
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Just talk bikes.What else is there?

Always have a 'Plan B'

[Slimmy]

Yes I am using the cd200 carb and it has the correct size jets in, clean filters etc and I am using the 12v coil from cm125

Thanks for the help

Maybe my carb is just no good as it was stood for years from previous owner

Got me baffled
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Slimmy

[Slimmy]

Using the 12v stator from the cm125, has this caused some sort of compatibility issue? For example not sparking in time as the engine used 6v stator previously, I’m just guessing here
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Slimmy

[Slimmy]

update, i have done a compression test and found low compression in both cylinders, around 60psi and 75psi wet.

so decided to have a look and sure enough the piston rings were worn, not massively over the Haynes manual service limit recommendation.

so my question, with the low compression I have would that of been the cause of my original problem or just another issue on top.

also looking at the valve heads they are very black, should I clean these up or is that just how they get?
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Slimmy

[Robby]

You're doing a top end rebuild, and cleaning up the valves and grinding them back in is part of the job.

Low compression could have something to do with the plugs sooting up, along with the other things that happen because the piston rings are worn.

Revs hanging is usually a sign of an air leak. Either inlet manifold poorly fitted or missing a gasket, or a cracked inlet, or you're really unlucky then it could be worn seals on the throttle butterfly spindle, so its sucking in air there.

The whole things need a proper going over. Piston rings wearing out is fairly rare, and suggests a lack of maintenance. Inspect the camshaft before you spend any money on it - or see if the one from your 125 engine is close enough to work. It is from the era when small Honda engines really needed frequent (~1000 mile) oil changes. If they didn't get that, they were liable to knacker the cam, the head, or both.

I almost forgot, standard answer - pass your test and get something decent. It would be embarrassing to get caught riding illegally by using a CD200 engine as a "performance upgrade".

[steve the grease]

Theres no way anything will run with compression below 100psi. Should be 150 plus to run properly ( my old Honda 125 was specced at 170 psi)

[Nobby the Bastard]

A CM125 must be really crap to think that a CD200 would increase the power.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Teflon-Mike]

why-do YOU WANT A cd200 MOTOR IN A cm125 frame to begin with?

If it's some bit of criminal mastermind to cheat Learner restrictions, look again; as stock and in good fettle, the 200 Benley barely makes the 15bhp permitted on an L-plate... it just has too many cc's. CM is also hardly a 'sports-bike', and with soggy twin-shock suspenmsoin and semi cruiserified geometry, hardly has the ingredients to make much of any extra oomph its given.... And wot you got be dodod anyway....

Before doing much more I would want to be pretty clear what I was tryingf to achieve...

See:- HOW2: Top End Rebuild Honda CB125 (Benley Motor)

Whether top ending the CM125 or CD200 lump, you are looking at the thick end of £200 in parts. Doing the 200 rather than the 125 gains you little, and probaby makes life harder to choose bits. Barel kits for the 125's are pretty commonmon the bay from china, 200's less so, and the 53mm bore barels have thicker liners and larger liner rebates in the crank cases, so using cheaper/more common 125 barel kit wou;d noy be a straight swap, and ISTRT that the gudgeon pin diameters differ also.

Hence probably as much work and money and less risk/hasel to recondition the CM engine.... and probably as much useful performance to be found.

If doing doe cheaps, then it aint really.... be better of cashing in the CM and sticking recon costs towards, well for cheaps or performance, a full licence, if you dont have one; plenty of sub £500 big bikes on the market and most of them, apart from a CD200 tend to have a lot more oomph for it! Can be cheaper to insure too.....

Else-wise, sorry to dis youyr pride and joy, but the CM125 is only as powerful as a CG125 poush-rod single, and no more economical.... smoother perhaps, more stylish... debate ably.... but the bottom line is that it offers bludger-all over any other 125 Learner bike.... so if dead, why try revive it, let alone mod it too?

Nut the answer is,motor need rebuild....See:- HOW2: Top End Rebuild Honda CB125 (Benley Motor)
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Slimmy]

Thanks for the replies guys gives me more to think about and some very good points made!

I love my little cm, it rides nice and always gets a lot of attention when parked up at work.

wanted a little more mid range grunt, I know it would still be slow compared to others but hey nothing ventured nothing gained plus I enjoy the tinkering lol

thanks again for your time guys
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Slimmy

[Easy-X]

I read somewhere there's a 250cc version of my faux-cruiser sold in Pakistan. "Hey! When I get my full licence I could ship over a cheap engine and get a bit more life out of it!"

But then, no. A few more horses aren't going to auto-magically do anything for the handling... so that'll be new suspension and better tyres. Oh, and if does go faster I'd probably want better brakes.

Hang on, why not just get another bike?! People are queuing up with offers on the Superlight just as it is. Start really dicking with it and it'd probably be worth a lot less (given the insurance companies won't know what to make of it.)
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Teflon-Mike]

I have briefly had a CD200 lump in a 125 S-D. It was absolutely no faster; the extra ponies just aren't enough to make that much odds; might have been stretched a bit muggering with sprokets, but CD200 has 4-speed gearbox, and rides on the low down stimp. It is actually quite nice, but I wouldn't chuck reconditioning money at a CD200 lump, to make a CM less valuable, less insurable, and not a lot better OTR.

Of the big bore Benly's, the CB-Two-Fifty lump would likely be gavourite for a straight swap... reletively cheap in the breaklers, and in good fettle, 19hp, five cog-box and a straight swap... that would be the cheaps way about with plusses for cheaps using take oot motor that does actually have a little exta oomph..... but still money I would query spending at all.

If you want a bigger bike, then there is little to stop you have one, apart from lience, and its likely easier, cheaper, safer, and as much charecter, or more than the CM125... go look at the small adds.... see whats on offer; pay heed to the Chinky made AJS raptor too, a cm/rebel clone they chucked the 233 lump into and even offered as a dealer conversion......

Otherwise, plenty of126-400 cruiserettes out there, none very sought after or expensive, all you need is a licence..... no spanners requied;' likely less to sinsure bludger all more to tax, just as ecconomical and nice to look at and ride.... L-plate restrictions are utterly self imposed... id upi dont want to suffer the4m, all you need so is take the tests, and they is hardly brain surgery..... and if you an taxkle the daily commute on L's no reason you cant do it once for man with clipboard, for less than price of repeat CBT......
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'