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Old 10-24-2010, 07:17 PM   #1
tonysmallframe OP
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Ultimate CT-90 motor?

I've been becoming more familiar with my CT-90, and wanted to get some advice on the ultimate motor, knowing full well that the best motor for it is the one that is currently in it. I'm looking for a bit more speed, (who isn't), and the ability to have a manual clutch in mine, without a real decrease in fuel economy or reliability. I know that you can always just drop a 140cc Lifan or YX160 stroked out to 180cc, or something crazy, but I have reservations of doing so. I already have a decent starting block in the CT-90 motor currently in the bike, and a swap to anything else would result in the loss of the high-low range box, one of the things that makes the bike special. Too much horsepower would also overpower the braking and suspension rather quickly

I'm thinking that building up the current CT-90 motor with a S-90 clutch cover and clutch, along with a SL-90 shift drum for 1-N-2-3-4 shifting would fix my reservations with the auto clutch.

The Powroll bore kit and stroker crank, although expensive, would upgrade the current block to a bit under 124cc, and the stuff sounds bulletproof. Alternately, I'm looking at the ATC125 top end and crank and seeing if either of those would work. Stock exhaust would still work, at least with the Powroll stuff, and i'd be interested to see if the stock carb has enough flow to be rejetted for the larger displacement.

Disadvantages include cost - the Honda stuff is cheap, but the Powroll stuff isn't, and i'd still be running points. The points are a pain to adjust, but I haven't had a set go bad on me in a while - and unlike a bad CDI, i've always been able to limp home on points after issues.

I suppose thats a lot of thought for a cheap scooter - but i'm just trying to see what knowledge is already out there. Looking to do some longer tarmac events next year, possibly the Lake Erie Loop if I can get up that way, along with covering a good bit of the TaT. So, what would you run if you had the choice?
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Old 10-25-2010, 05:27 AM   #2
hugemoth
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I would take the leap and put in a good Chinese engine. It'll be easier, cheaper, more reliable, and faster. You'll have your manual clutch, electronic ignition, 12V electrics, and it'll run with a dead battery. You'll never miss the dual range, in fact you'll enjoy not having to stop and switch it.
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Old 10-25-2010, 11:09 AM   #3
Jacl-Kampuchea
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Google benley 50 and 90cc bikes. Identical to the cubs but look like a classic moto and have a conventional clutch. Parts should be available from a dealer and bolt right on.
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Old 10-25-2010, 05:59 PM   #4
tonysmallframe OP
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Jaci - the Benley 50cc/90cc are super similar to the SL90/S90 over here. Found most of the parts to convert over used for well under $100 or so.

hugemoth - I was looking at the Chinese route for a bit, but after getting some crap pattern parts like carbs recently I had more faith in a rebuilt original setup than a new Chinese motor. Any suggestions on good brands - and their distinguishing marks? Don't need to be getting a copy of a copy of a copy of a Honda motor.
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Old 10-25-2010, 06:40 PM   #5
hugemoth
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The only Chinese brand I have personal experience with is Lifan. I converted a 68 and a 71 model Trail 90 a couple years ago to 110cc Lifans with manual clutch. One has over 2000 miles and the other over 3000 with zero problems. I also have a 200cc Lifan dual sport that just turned over 24,000 with zero engine problems. My opinion as a former motorcycle mechanic is they are better than the original Honda engines.


Quote:
Originally Posted by tonysmallframe
Jaci - the Benley 50cc/90cc are super similar to the SL90/S90 over here. Found most of the parts to convert over used for well under $100 or so.

hugemoth - I was looking at the Chinese route for a bit, but after getting some crap pattern parts like carbs recently I had more faith in a rebuilt original setup than a new Chinese motor. Any suggestions on good brands - and their distinguishing marks? Don't need to be getting a copy of a copy of a copy of a Honda motor.
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Old 10-25-2010, 07:07 PM   #6
YamaGeek
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I have to concur with Hugemoth, my Lifan 100cc is the smoothest small single I've ever owned, even compared with the small bore two strokes I've had in the past. My Lifan engine has very little vibration at speed. I've got well over 5000 miles on mine and a couple of full days riding with average cruising of 40~45 mph. The Lifans also come with 3 plate clutch in the 100 to 125 cc size. Totally underrated, and cheap to operate

The SL125 top end will be problematic trying to convert to the horizontal engine case, as the studs are longer and are much further apart on the 125 vertical cylinder engine side cases. Not impossible, but mucho money in refabbing the old horizontal sidecases. You might as well buy a Honda TL125 and do a swap to a XL 175 engine with the 6 speed gearcase.
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Old 10-25-2010, 11:35 PM   #7
Jacl-Kampuchea
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Also, have you considered the 125cc engine from a Honda Wave or Honda Dream?

They are quite pokey and (I guess) that the scoots they come in have heavier frames than your older CT.

A friend has one in a '60's C50. Easy fit.Don't know about making it fully manual I'm afraid.
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Old 10-26-2010, 02:29 PM   #8
KI6HNB
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Check this place out.

http://www.dratv.com/honcttrail90.html
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