Lack of power (part 2)

Since I can't find any trace of my "Lack of power" thread from 7th May
in google groups archive (a consequence of google being down for a time
I guess), and I use google groups web interface to post usenet, I can't
reply so I'm posting this as another thread.

For those who didn't see or read that thread yesterday I posted
explaining that I felt my bike was suffering from a lack of power.
Yesterday it was the first time I had taken my bike out for a good ride
after a chain and sprocket change. I found the power delivery was
completely different. From the speed and revs I supplied yesterday
most suggested I may have a clutch slip problem. I also remember one
person saying that if there was pull all the way up then it is most
likely due to the sprocket change.

Because the speed and revs supplied yesterday were mainly from memory
throughout the ride I decided today to run a test on my bike. So I
found a road with a mile straight and a roundabout each end. Perfect.
Here's what I found:

Bike (CBR600F) red lines just after 13k.

2nd gear 13k revs = 80mph
3rd gear 13k revs = 110mph (ish)
4th gear 12k revs (ran out of road before I could take it further) =
125mph

There was pull all the way up the rev range and I guess power delivery
was smooth throughout, i.e. the same amount of pull no matter what rev
range I was in. It also seemed that I had to open up the throttle a
lot more than I used to to get a response particularly low and mid
range.

I'm no expert and I'm still learning how differences in sprockets can
affect power delivery and feeling of the bike but I'm guessing that
from the above there is more top end speed available at the expense of
lower end and mid range grunt. Is this correct?

If it helps the chain and sprocket set I had fitted was a DID
Professional X RING (Gold plates).

So anyway back to the question of my original post, am I paranoid in
that there is nothing wrong with my bike's power delivery, only that it
has completely changed so I don't recognise it any more? I really miss
the lower end and mid range grunt. This was so much better for me
taking my bike out for a spin on the A and B roads.

Or is it that there is possibly a clutch slipping problem?

I'm well confused.

 

if you can accelerate hard and run the bike up to 125 then it doesn't sound
as though your clutch is slipping

 

If the bike has an electronic speedo and the sprocket sizes have changed
the bike will now be giving false speed readings.

Modern electronic speedos generally look at what gear the bike is in
what the revs are and calculate the speed.. Change the gear ratio and
the formula is out of whack.

HTH

 

1998 mate. I believe it's the CBR600F W model.

Aye before I had the change in sprockets I always remember in 2nd gear
30mph was 3000 revs. I remember because in my IAM training they made
me stick to 30mph, rightly so, in 30mph zones and the feeling of the
engine at 3k revs was the easiest way for me to do this without having
to continuously look at the speedo.

No I've had the bike for just one year and I didn't know the size of
the sprockets that were on there, and I didn't think to take a look
either before I took the bike in for a change. I do plan to call the
previous owner (details in log book) to quiz him though. And I will
also phone the bike shop too. The bike performs so differently now.

That's good news.

Thanks for your help Champ.

 

Analogue speedo mate, I have the 1998 W model.

 

Sprocket sizes here : http://www.motorcycletyresuk.com/Services.htm

 

you may find the previous owner altered the sprocket sizes to give it that
low down umph you said is not there any more

 

Of course! - I'd forgotten that, too. So, not only will changing the
gearing have changed the revs used for a particular speed, it'll have
changed the speed reading too.

<thinks>

But won't the effect be self compensating?

 

Ah. In that case the previous owner may have shortened the gearing,
which would have given better acceleration at the loss of some top
speed, and 'revvier' cruising. If the bike shop fitted standard
sprockets (which they almost certainly would have) then that would
explain the change.

Ask him if he changed the gearing.

No worries.

 

If the speedo is reading from the gearbox sprocket? I lowered the
gearing on my FX model by going down one tooth on the gearbox sprocket
and it definitely altered the speedo reading. IIRC it was over-reading
(sprocket was going round faster for a given 'real' speed). I couldn't
work out why the fuel consumption dramatically improved until I realised
that the mile-ometer was over-reading too. I was getting more iMPG.

 

CBR600 1997 -2000
Primary reduction 1.882
Final Reduction 2.812
1st gear 2.833
2nd 2.062
3rd 1.647
4th 1.421
5th 1.250
6th 1.130

CBR600 FV,FW 97-98
Front Sprocket 15
Rear Sprocket 43


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ColonelTupperware,
spouting bollocks on Usenet since 1997
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So the speedometer on a modern bike shows 30mph or so when you are
stationary in first, revving the engine, about to move off.
And if you declutch at 70mph, allowing the revs to drop to tickover,
the speedo reads 20mph.

Perhaps a modern speedo is driven from the gearbox output shaft.