Ct90 to 110 upgrade

[Biggut]

I weigh in at about 230 lbs. most of my riding is between 6500 ft to 8000 ft. I’m not able to climb grades that I did when I was 30 lbs lighter. The ct 90 is running well. My questions are; would I notice an appreciable power gain if I increased the cc’s to 110, and I don’t even know the limits that I can increase to. I won’t be putting in a different engine. I just prefer to work with what I have

 

[Old Guy Too Many Bikes]

In my experience, CT110's aren't appreciably faster than CT90's. I'm assuming your bike is jetted for high altitude already. Dropping a YX 140 in there would be like night and day, but since you say that's not an option, I'd just install a rear sprocket with about 3 or 4 more teeth and be done with it.

 

[kirrbby]

When you say you can't climb grades...are you talking about climbing them at high or low speeds? 2nd gear or 4th gear?
I'm not a CT90 guy, but I always think of them as being great hill climbers...mountain goat kinda bikes...
Do you know for SURE if the sprockets are the stock sizes?
I would count teeth. And maybe do a compression test to see if your top end is in good shape still.

 

[nightgrider]

I believe depending on the year CT90s also have a Low and High gear reduction case to help torque multiplication for off road riding.

 

[Old Guy Too Many Bikes]

You're right about the dual range transmission, but the low range is too low unless you're going up stairs. The unfortunate thing about the CT90's is that you can't swap out the front sprocket. The high elevation that Biggut has to deal with doesn't help either.

 

[Biggut]

I like the more teeth sprocket idea.

The problem is with a particular trail I ride. Probably a least 9,000 ft. Steep, deep rutted and slippery. And it’s a tight right hand turn. I run the 90 in low range, 1st gear, balls out. I may even try some premium fuel.

Thank you all

 

[Old Guy Too Many Bikes]

That would be tough on any small bike. Did you do any jetting changes to compensate for the altitude? Get a rear sprocket with about 4 more teeth. That would be about a 10% increase in rpm. That should give you enough torque in 1st and low to granny you out of anything.

 

[gpzkat]

Premium won't provide any more power, just more knock resistance for a compression engine. What you need is a turbo

 

[fatcaaat]

I don't see how it's humanly possible for a well-running CT90 to struggle with going up anything in low range, first gear, regardless of how encumbered it might be. I have played with a lot of CT110's and it would throw me off the back before it stopped climbing. However, you can do a few things to improve the power on them and the CT90 actually has more options than the 110. First make sure compression is in limits. If you are going to redo the top end, opt for the big bore kit which is 3mm larger. If you are patient and keep a look out, periodically you can find stroker cranks show up on ebay for them (atc) but not necessary. Since you are running rpms up, find a midrange cam for it (webcamshafts.com) do a little portwork (not much) and swap the carb to a mikuni VM20. Keep the stock exhaust. Premium gas won't do anything unless you bump the compression ratio so don't waste money there. All that in addition to sprocket changes. BTW you can swap the front sprocket on a CT90...you can choose between 14 and 15t only.