I have a Honda CBF 125 2010. It had a new chain and sprocket set fitted about 3-4 months ago and I have tightened the chain again since then (about a week ago). I have poor acceleration when I come to any type of upward incline. I will be in 3rd gear going about 22 mph and change to 4th when I get to about 35mph. Normally as soon as I change, the RPMs Drop straight down and it doesn't matter how much gas I give, the bike doesn't accelerate and the RPMs don't even move on the dial. This means that if I was at a standstill before the incline my bike will take about a minute to get to about 25mph uphill (but still only really feels like im going under 20mph). Even if I am lucky enough to have a 'running start' i.e. im driving about 30-40mph coming up to the hill, as soon as I actually start driving uphill the RPMs still start dropping even while increasing the amount of gas (which just makes the engine scream and RPMs do not increase). When this happens, I will try dropping a gear, but all this does is makes my engine scream as im obviously going to fast to ride in that gear.

I thought it could be my Air filter being too clogged up as I have neglected this for about 10 months. When I took out the air filter, it was dirty, but not as much as I was expecting. Admittedly, the bike does accelerate slightly better now since I have taken it out and cleaned it until my new one is delivered, however, cars are still having to overtake me uphill.

I also wanted to check if my clutch may be slipping, as a mechanic mentioned that it sounded like it was skipping 4th gear and going straight to 5th. To check, I put my bike into 2nd at standstill and tried to pull away. The RPMs increased and I was able to pull away just as well as I would in 1st gear - So I was told that my clutch is most likely fine if my bike is able to move off when doing this.

Is there anyone who has any idea what else this could be?!

Does anyone have any idea what this could be

  • Welcome to Motor Vehicle Maintenance & Repair! Jan 14, 2019 at 15:33
  • If the engine is making more noise as you give it gas but the RPMs are not encreasing, then you also have a tachometer problem. Have you changed you oil? Did you use a proper motorcycle oil, as it's different from a car engine oil because most motorcycles have a wet clutch. With improper oil it will slip. Try this, get on your bike get to about 30mph(60kmh) get into 5th or 6th gear and wack the throttle open. This will tell if it's slipping.
    – dmb
    Jan 14, 2019 at 19:23

1 Answer 1


Does this model have a carburettor? If so, it may be worth checking that there is adequate fuel getting to the engine. May be a clogged jet or float bowl issue.

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