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I ride a Honda Rebel 250 motorcycle and over the past few days I find that the bike is losing power when accelerating fast.

When I twist the throttle to accelerate quickly (in any gear) I hear the engine sound increasing in pitch by a lot more than I'm used to hearing, but the motorcycle doesn't seem to respond and performance is very poor. If I then twist it back to a position of slow acceleration, the engine noise returns to I'm used to hearing (still the accelerating noise but a lot lower pitch) and the performance also seems to be appropriate to that level of acceleration.

What could be wrong with the motorcycle?

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I am having the same issue, I have a 125cc ajs regal raptor, and if I am accelerating in well its mainly 4th gear and going up a slight incline it'll lose power and even if I knock it down into 3rd it'll struggle, but I think I may have a block in the air fliter or in the carbs, so it needs sorting, just something to think about next time you have a similer problem mate – user3632 Sep 3 '13 at 20:25
    
@AdamRobinson the key here is that the RPMs increase without the motorcycle accelerating. This is the hallmark of a slipping clutch, and could not be explained by blocked air filter or carb issues. – mac Sep 4 '13 at 15:49
    
I'd like to add another worn clutch symptom courtesy of my old Bandit 600; surging when riding at speed. What I think happens is that the clutch can't transmit enough power to overcome the drag when going fast (in my case it was 60mph) so the clutch starts slipping, then heats up and the plates expand, then the expanded plates provide more friction and the clutch stops slipping, then the plates cool down and shrink, repeat ad nauseam. – squigbobble Mar 3 at 12:06
up vote 17 down vote accepted

My knowledge of motorcycles is limited so I could be wrong, but it sounds like the clutch is slipping.

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2  
I've had a mechanic look into it and yes, the problem was the clutch slipping. – Paulo Pinto May 16 '11 at 21:17
    
Did he say why? Is it just worn out, or something to do with the oil? – theUg May 25 '12 at 4:20
    
The clutch plates were worn out. – Paulo Pinto Nov 15 '12 at 17:34
5  
Do you tend to ride with your hand on the clutch lever? if theres no play on the clutch lever you could accidentally be causing wear by keeping it slightly "on" – Mauro Mar 8 '13 at 8:18

I realize this question has been answered, but keep in mind that any carbureted engine can bog down under throttle and cause a lack of acceleration.

If it can be backed off and regain acceleration, then I'd suggest carb tuning. If the engine revs, but no acceleration then it's a slipping clutch.

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There are two cases to be considered here both the carb and the clutch could be culprits here. Let me explain.

If the engine warm and is at the normal operating temp and you floor it and no acceleration that means the culprit could be clutch.

If the engine is not warm enough and it has only been about 5-10 minutes then it is the carb, there is a specific term to explain this phenomenon. In this case you floor the throttle and poor response and if you go easy on the throttle and you get the corresponding acceleration.

Before you confirm it is the clutch ride it for about good 30 minutes and then roll the throttle like mad and see which case it falls under.

but don't forget to check the adjustment to the clutch make the cable little tighter and see if it makes any difference, this is a simple thing to do and hurts nothing, you can revert it back real easy.

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protected by Zaid Aug 26 '15 at 15:04

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