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About my bike

  • Model: Honda CBR 250R
  • Total Run: 35000kms
  • Total Time: 2 years 3 months
  • Clutch Plate changed at 30k kms after an accident
  • Engine oil, engine oil filter and air filter changed in last service

Problem Statement

A while back I observed that my bike is giving a very low mileage. It use to run 450 kms on a full tank (13 litres) while now it just runs 380kms.

I am not sure if that happened after clutch plate change or last service. And am having hard time figuring out the true cause.

Please help.

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  • I wonder if the clutch is slipping? I'm not very useful when it comes to bikes outside of general running kind of things, lol. Hopefully @DucatiKiller will happen along. There are a couple of other bike guys on here as well.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 26, 2015 at 23:54
  • To be honest,, your bike is actually giving one of the best F.Es among the CBR250Rs that I know of even with the problem you are stating. will answer once i get time.
    – Shobin P
    Commented Jun 27, 2015 at 3:58
  • @Anarach: did u get time?
    – Ut S
    Commented Jun 29, 2015 at 5:34
  • Does you bike rattle or is it smooth?
    – Shobin P
    Commented Jun 29, 2015 at 6:25
  • @UtS Are you still having this issue? If you have solved it, could you populate the answer and award it to yourself? If not, can you share any additional troubleshooting that you have completed? Are you using the same fuel type from before? Have you ever changed the spark plugs? Do you have any type of check engine light or indicator of an issue?
    – DucatiKiller
    Commented Dec 12, 2015 at 3:05

2 Answers 2

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Background

This is a common issue with shim and bucket valve trains. As the valves are getting worn into the head a small groove is beat into the valve face after opening and closing so many times. As the valve pushes up into the head it takes up clearance between the cam lobe and the bucket which the cam lobe depresses to push the valve in and open it to either release exhaust gasses or allow intake mixture into the the combustion chamber.

Possible Issue

As the valve gap is taken up over time a new shim that is thinner needs to be inserted under the bucket. This is a normal maintenance event to add clearance between the cam and the bucket. If this is not done, a gap between the valve face and the head can form, typically this occurs on the exhaust side (don't ask me why) and the gap creates an exhaust leak, essentially allowing exhaust gasses to escape during the combustion process. In the beginning stages of this, fuel mileage decreases as does performance. In advanced stages the bike will not start or it will run extremely poorly.

Solution

Adjust the valve clearance to fit within service limits.

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  • 2
    How do I confirm that this is the problem? Also, how is this adjustment done?
    – Ut S
    Commented Jun 29, 2015 at 5:33
  • @UtS - you would remove the valve cover to expose the camshafts and measure the valve lash between the cam lobe and the valve bucket. You can ask another question about how to measure and adjust valves on a shim and bucket valve train and myself or someone else will respond.
    – DucatiKiller
    Commented Jun 29, 2015 at 7:38
  • Are you still having the issue? Where you able to make any headway?
    – DucatiKiller
    Commented Jan 12, 2016 at 0:43
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Issue got resolved in next service. The problem was the with the rotor. Front wheel rotor was touching the caliber causing too much resistance. On close observation it seemed that rotor its shape after a bike fall lately. Replaced it with a flat new rotor and was able to drive 420 kms in full tank.

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  • It's really odd that you didn't feel your front end diving and the resistance during normal riding.
    – DucatiKiller
    Commented Feb 2, 2016 at 17:09

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