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Old 06-05-2014, 12:23 AM   #1
MNzach OP
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CT90 big bore...

Alright I've got a 77 ct90 and was thinking about getting the dr. atv big bore and cam to give it a little bit more get up but then I saw this http://www.ebay.com/itm/110cc-Kit-Bi...p2054897.l4275 Has anyone used this one instead? It would be easier than having the old one bored out and I could always go back to it if I didn't like the new one.
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Old 06-05-2014, 08:41 PM   #2
fullmetalscooter
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Quote:
Originally Posted by MNzach View Post
Alright I've got a 77 ct90 and was thinking about getting the dr. atv big bore and cam to give it a little bit more get up but then I saw this http://www.ebay.com/itm/110cc-Kit-Bi...p2054897.l4275 Has anyone used this one instead? It would be easier than having the old one bored out and I could always go back to it if I didn't like the new one.

From my reading here most rather go to dr.atv and do an engine change out by getting one of the kits they sell . That way you end up with a replacement engine to save or sell.
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Old 06-06-2014, 01:29 PM   #3
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If you swap out the motor (for a non original one) you loose the dual range transmission - which is a big part of the CT's appeal.

I did the DRATV big bore, performance cam & 22mm carb to my '75. I'm happy w/ it but for the price of that ebay big bore kit, I might have done that instead. You'll still want the Dr's cam and a 22mm carb.
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Old 06-06-2014, 05:39 PM   #4
MNzach OP
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Yea, the dual range is the main reason I haven't just swapped a Lifan into it. I think I'm gonna give this a shot whenever I get free time again. If I don't like how it works I can always put the stock cylinder back in.... but I doubt that would happen.
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Old 06-11-2014, 05:37 PM   #5
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The dratv piston is 53mm or 54 mm.That kit has a 52 mm cylinder.The head gaskit in that kit does not look correct for a ct90.If you make the engine bigger you will have to rejet the oem carb or get a new carb+ possably do some jetting work.I have a 1969 sl90 with the dratv 54mm piston+cam .The engine had a 22mm carb oem.My jetting is 92 main 38 pilot.With the 54mm piston you get 104cc.With a 52mm piston you will get 96+cc.The ct90 engine needs more stroke.I am working on a 125cc+ engine using a atc125m crank.The air intake in the rack is restrictive.The easiest hop-up I ever did on a ct based bike was a ct110.I removed the rubber boot from the rack and the baffle from the muffler.Then I put in a bigger main jet.The owner was very happy.
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Old 06-30-2014, 03:02 PM   #6
MNzach OP
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Thanks!

Thanks for the info! I didn't make the connection to the different size compared to the dratv piston. I'll have to do some more research before I do anything.
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Old 09-02-2014, 07:53 PM   #7
injuhneer
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So what did you finally do? I am working on a 146cc dual range motor for my ST-90. The thread is over in the "Old's Cool" forum.
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