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Discussion Starter · #1 ·
Hi,
I want to change the drive sprocket on my 2020 CB300R, going from 14 tooth to 15 tooth, to make the gearing a little longer. My question is, do I need to get a longer chain? I know when changing sprockets hou need to replace the chain anyways, but the bike only has 1000 miles and i ride super conservatively, i dont take off super hard or go full throttle all the time, so the chain is in really good shape. Im only worried that if i put a bigger sprocket on the front, the chain wo t fit. Thanks ahead for any info!
 

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One tooth on the front sprocket should not be a problem, chain adjustment should cover that. When I got my bike it had one tooth smaller than factory. I didn't like it and went back to the original tooth count, one up from the sprocket that was on it. It adjusted fine. Rear sprocket changes might require more or less links.
 

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Discussion Starter · #3 ·
Yea, I got it done a week ago at the dealership that sold me the bike and it is fine, no longer chain needed... The only thing, the sprocket cover wouldn't fit so they had to take this metal piece off of it, that "holds/guides" the chain(?). Apparently that metal piece is there in case if the chain breaks it doesn't put a hole in the motor.... Which I found very weird, cuz that metal piece was attached to a plastic cover and held in place by two tiny plastic pins... They had me sign a paper saying that if the chain breaks and damages the motor, they are not responsible for it. The bike rides much better now with the new sprocket, much smoother and I dont have to shift every 2 seconds..
 

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Discussion Starter · #5 ·
Yea, ive the sprocket on for a week or so, put 20 miles on it. I keep checking after each ride and it's fine. Quick question, maybe you would know - I took the air filter out today, just to clean the airbox, make sure everything is ok, and behind the air filter (thst secondary airbox) it was a little wet and smelled like gas a tiny bit. It wasnt a lot of "fluid", just a tiny bit.. Is that normal??
 

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If it were me, and the bike was running okay, I wouldn't worry about it, but I don't know if it's normal or not.

I have seen carburetors on cars spit back a little fuel in years gone by and they ran okay.
 

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Discussion Starter · #7 ·
It runs fine, backfires a little on deceleration (which i like, sounds mean). It's fuel injection though, not a carb. I noticed inside the secondary airbox, there is a little drain hose... So it must be normal for it to spew a tiny amount of fuel, i guess. Im gonna call the dealership on monday and talk to the service dept.
 

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Wot RG said. Carbs do spit back a bit with high lift cams.
Usually the gearing is said that at WOT, wide open throttle in top gear, you attain maximum revs, or maybe a bit less.
A bit can be 500 revs for a slow reving motor, and 1000 revs for a high reving motor. The reason is you are getting maximum horsepower when it is needed most. That is pushing air which seems to get quite thick causing a lot of drag over 90 mph. Being short a few revs may get you around the maximum torque for the engine, which is still okay. But dropping below maximum torque in top gear at WOT, is making the engine work harder than it should.

Here is an example, from memory. My 400 cc bike makes maximum horsepower at 10,000 revs, and maximum torque at around 8800 revs. I can not reach 10,000 revs in top gear, mostly due to the extra drag of all the gear I have bolted on. I can reach 9,000 revs which gets me over the maximum torque number. If I raise the overall gearing, I go slower at WOT because I am not reaching the maximum power ( torque or horsepower ) of the engine. However I am improving the rideability of the bike in the lower gears.

Your question. Usually changing the front sprocket does not require a new chain. There is enough movement in the rear axle to allow for it. The other option is to use the stock front sprocket and have the safety barrier, and go smaller on the back, and then might be enough room to adjust the chain. We used to use full and half links for this, but that is not the case these days.

UK
 

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Discussion Starter · #9 ·
Wot RG said. Carbs do spit back a bit with high lift cams.
Usually the gearing is said that at WOT, wide open throttle in top gear, you attain maximum revs, or maybe a bit less.
A bit can be 500 revs for a slow reving motor, and 1000 revs for a high reving motor. The reason is you are getting maximum horsepower when it is needed most. That is pushing air which seems to get quite thick causing a lot of drag over 90 mph. Being short a few revs may get you around the maximum torque for the engine, which is still okay. But dropping below maximum torque in top gear at WOT, is making the engine work harder than it should.

Here is an example, from memory. My 400 cc bike makes maximum horsepower at 10,000 revs, and maximum torque at around 8800 revs. I can not reach 10,000 revs in top gear, mostly due to the extra drag of all the gear I have bolted on. I can reach 9,000 revs which gets me over the maximum torque number. If I raise the overall gearing, I go slower at WOT because I am not reaching the maximum power ( torque or horsepower ) of the engine. However I am improving the rideability of the bike in the lower gears.

Your question. Usually changing the front sprocket does not require a new chain. There is enough movement in the rear axle to allow for it. The other option is to use the stock front sprocket and have the safety barrier, and go smaller on the back, and then might be enough room to adjust the chain. We used to use full and half links for this, but that is not the case these days.

UK
Thanks for the reply. Ive the front sprocket fit fine, did not need a new chain.. i drives much better now. My bike is FI not a carb though. With a carburetor i would expect a little backsplash but im not sure if thats the case with the FI engines.
 

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How close is that motor to the one on the 2015 CB300F. I haven't kept up with them much since I bought my daughter one. It is out in my garage. I had a complaint with it initially until I realized I was running it into the rev limiter. It wound up so fast the way it was geared that it was there before I realized it and so quiet you couldn't ride it by sound. It would stutter and I thought there was a problem. The problem was me, being used to old school liter bikes, that didn't spool up so fast. I remember hearing the same complaint on some of the forums and had a chuckle that I wasn't the only dumb ass out there.
 
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