Honda CM 125 to CD200 - Carb and Engine Set-up

[doombug11]

Hello there!

So I decided to upgrade my little Honda CM 125's engine, since passing my test and jumping up to a VFR 750 the little bike feels somewhat dangerous out on the open road with my fat arse lumped on it, at 6 foot 4 I rarely get past 55 on any 4t 125 maybe 60 on a nice motorway with a gradient. As my only mode of transport I would like to keep the little bike, its not really worth much so theres no much point in selling it and its great for popping round town, it just needs a bit extra speed! So I heard it was possible to shove a 12v CD200 engine straight in to my bike so found an old one that had been sitting for a while for £45 of ebay.

Looked a bit dirty but it had good compression so thought it was worth a shot, quite handily all the bolts holding old mountings that looked rusted solid in the photos had been coated with grease at some point and came apart really easily so fitting it went really smoothly.Changed the oil, bodged the cables together and using the spark plugs and carb from the 125 set about giving it a kick, got a flash of life on the 3rd kick and it came roaring back into action a few more later. Quite chuffed with that, got ripped off on a dodgy 125 engine back in the summer for 150 quid that pissed oil everywhere (though it kept me mobile whilst i rebuilt its original motor) and another for 180 i got my money back on that blew a spark plug the first time I rode it!!

Sounds really nice, and sat ticking away at idle pretty quickly, sadly the clutch was seized but wasn't a big issue just had to take it out and give it a clean. At first it refused to go into first, though it was pulling away just fine in 2nd so took it for a spin and after a few trips round town it worked itself back in again. While the power is quite decent at the lower revs it doesn't like being revved to high and chokes out as you open the throttle.

So now I've got it in motion I need to set about getting the engine set up properly, I dont have a manual for the 200 so was hoping someone could help me with some specs and settings, namely what spark plugs to use and what valve clearances to set the tappets to. The engine came with a carb but the throttle slide was seized, I'm going to attempt to clean this up and see if it works but it would be great if someone had the specs for the carb, float height, pilot screw turns, jet size etc.. Hopefully get it running nicely!!!

[temeluchus]

a quick Google and:

26 mm Keihin carb, Slide Type (PD 33A TA) with 110# main Jet and 42# Slow Jet(single Carb).

spark plug is cr7hs.
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Some shite cruiser. Now with guns and FREEDOM!

[Teflon-Mike]

Not dropped a 200 Benley into a CM, have dropped one into a Super-Dream. works very well, actually.
360 degree motor is lumpier than the Twin Carb 125's 180 lump. Stock, it punts 15bhp, which is a tad more than the UK spec Super-Dream's 13, tad less than the older 'full-Power' T2's 17. Is up on the 10/11 of the CM and CD125's though, with their 360 Single carb motors... but it is that mid-range that is quite remarkable.
The extra cubes and the milder state of tune, suddenly there is so much 'flexibility' on the throttle. Actually completely changed the handling of the 125 Super-Dream, which needed revs to make thrust, and cornering was a case of tipping in, throttling on, and waiting for the revs to catch up to give you drive.. with the 200 motor, all of a sudden you have 'thrust' available just by opening the throttle, and can actually 'drive' the thing through bends... 'almost'... I say 'almost' like a 'Big-Bike'
Ran it on the CB's twin-carbs, and CDi ignition though, so may have had a tad more power/response, without that tortiouse twin-branch.

I suspect, though that big part of my initial shock at how strongly it pulled, though, was because Benley runs much taller final drive gearing, having only the four-speed box, and a lower top-gear drive ratio.

With twin-carbs and tacho, its pulling strongly to the 125's red line at 11K, and on the 125 Super-Dream gearing, that's enough to nudge the needle at the 80 mark. I suspect it could pull taller cogs, though doubt it would make it much if any quicker... but certainly wouldn't be quite so frenetic. 180-crank 125's like them revs, seems 360-crank 200's dont! On 125 gearing, though 1st is almost redundant, you can pull away in 2nd or 3rd...

So, I'd suggest you might like to mess with sprockets a bit to get the best from that engine. But also, I suspect that single 24mm carb will be rather strangling it.. 26 it should have, or better twins, will make it that much 'free-er'... though fuel consumption will suffer.. still good, but low side of 80 rather than high.
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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?'

[salem1987]

cd200 is a great motor in my opinion. As tef says, plenty of midrange grunt for a small engine and will last forever.

Just changed pistons and reseated valves on mine and it runs perfect.

Ultimate winter hack in my opinion!

Tef: Did you use the super dream inlet manifolds im assuming for twin carbs?

[Teflon-Mike]

[doombug11]

So here's where I'm at with this little project, I took the cd200 carb apart to see if it was possible to clean it up but the slide was seized solid, hit it with WD40 and a bath of petrol but it was wedged in there good. So decided as I have 3 other spare PD series carbs I would just force the slide out to recover the needle, jets and float and put them in another body. The slow jet was corroded in solid and annoyingly had no screw or bolt head to grip onto so was forced to leave it be, I'm only going to damage it forcing out so had to use the 38 slow jet from the 125, but I did recover the 110 main jet and needle. Annoyingly I hadn't thought the slide itself would be different but it is of course a heavier weight, too damaged from my extraction method I used the lighter throttle slide from the 125.

So in the end I ended up with a Frankencarb, put it back on the bike and took it for a quick spin round the country lanes. Engine ran really well, a little slugish on the lower end of the throttle this time most likely due to the wrong slow jet but it was no longer choking out when you opened it up. My word though that has made a difference! Just like you said Tef the mid range power transformed the bike, really pulled it through the corners, though being a CM frame and not the superdream it was of course still a bit wobbly!! I'm not sure quite how fast I got it either, the needle just bounced frantically between 60/70, though it still felt like it was accelerating, certainly faster than its ever travelled before!!

So with the little test ride over I need to sort out various bits, ideally I really want to go with this twin carb set up you guys are discussing, going to have to hunt myself down a pair in the new year, if I cant find any I'll just get a refurb kit for the time being. Had to order a clip-on air filter too, easier than trying to re-plumb it to the air box and I prefer the look of them anyway!

My biggest obstacle is the sprocket alignment, the counter-shaft looks to be about 10mm shorter than the one on the CM engine. From what I've been researching online it looks like my best bet is to get a fabricator to cut the teeth of one sprocket and the centre out of another and weld them together, when I eyed them up the offset looks to be exactly the width of one sprocket so should work I hope. Asides from that there appears to be people who are willing to make them but its pretty pricey!! Though I don't really want to have the chain jumping so I'm going to have to sort this one out.

[andymech]

I have a cd 200 engine in my cm. Mine is running a 14 to 34 sprocket set up seems to work well . I now have a full license but to be honest i have more fun riding this bike! I think the cd cm cb range are great bikes.
Does anyone know how you can date honda engines from the engine number?

[salem1987]

14 34! i tried 15 34 on mine and it felt like it was revving its guts out at 60.

Currently on a 17 front sprocket which is the biggest that will fit. 4th gear is more like an over drive so thinking a 16 will be perfect for me.

What gearing you guys running at?

[andymech]

[doombug11]

Had some hefty essays to be written this last month so hadn't had a chance to tinker with my little CM. Also had to wait a few weeks for my local bike shop to order in a clip on air filter, when I got this I took it for a quick ride to see how it was running and after a few miles it started to run like like a bag of shit, constantly stalling and needed full revs to get you going or it would kangaroo out on you. Went to make an adjustment on the pilot mixture screw and the bloody thing wasn't there!! (I forgot to put the spring in )

Got it home and the next day I finally got through the 42 slow jet I ordered and a new throttle cable. Fitted everything on, including a spare pilot screw with spring , naturally the pattern throttle cable was completely wrong, but I've finally got this little bike running well Ticks over nicely, runs well all the way up the powerband and doesn't half shift compared to the 125!

Had to piss about for a bit with a couple different gear change levers, the engine is slightly wider so for the CM lever to work it had to be positioned too low, I've got big arse feet so had to stamp on it with my heel to change down! So ended up using a random one I found in a box of spares, looks rusty and has a bodged handle but works a treat

Asides from a proper fitting and non-fucked throttle cable (I would like some consistent engine breaking!!!) All there is left to do now is sort out the gearing. Think I'm gonna go for 16-17 on the front, it has a bit too much acceralation right now, like you had Salem it tends to rev it self mental at 60+. Probably experiment first before I get an off-set sprocket made up, their quite pricey!! Got a friend who offered to attempt one, confident he can balance it but I'm not so sure!! Looking at 60 quid for one from the states or 80-100 quid labour from a local machine shop depending on how long it takes. Could just run it as is but at these prices for a small Honda sprocket my mates offer is looking rather tempting!

Here's a couple of pics of the old girl.

https://i802.photobucket.com/albums/yy309/doombug11/pic1_zps35d0fea8.jpg

https://i802.photobucket.com/albums/yy309/doombug11/pic2_zpsd794eec8.jpg
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1999 CBR900RR, 1984 CM200 (previously 125)