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post #1 of 14 (permalink) Old 08-08-2019, 07:51 AM Thread Starter
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Sprint ST955i suddenly revving 500rpm more

Afternoon fellow owners,

I have had my Sprint for a few months (2001 26k) now with only one niggle, it cutting out on deceleration occasionally, this has hopefully now been rectified.

Riding to work this morning, halfway through the journey my bike suddenly started revving whilst in gear and moving 500rpm more, this is through all gears but not at idle.

A few things were changed by the mechanic over the weekend to stop the initial issue (recalibrate instruments, closed throttle body position, stepper sensitivity).

Can I ask what may have caused this as all fine till about 30 miles in to journey. Where 60mph was 3500rpm it is now 4000.

Any advice or guidance most appreciated.

Bob

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post #2 of 14 (permalink) Old 08-08-2019, 08:34 AM
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Is it actually revving higher or is the tach showing higher only?

2002 Sprint RS: TOR silencer, LSL bars, Laminar lip, factory tail rack with Givi top box, custom painted OEM panniers (one of 'em anyway - sad story), M-Factory lowered pegs, Penske shock.Thanks for all the help, Kit!
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post #3 of 14 (permalink) Old 08-08-2019, 08:55 AM Thread Starter
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Quote:
Originally Posted by chickenstrip View Post
Is it actually revving higher or is the tach showing higher only?
Afternoon Chickenstrip, I would say it is revving higher as it is a little higher in pitch but being honest I cannot actually say with all sincerity.

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post #4 of 14 (permalink) Old 08-08-2019, 12:13 PM
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Virtually always leak at the IACV hoses - replace those, you will probably find they are cracked/perished especially at the nipples at either end.
You can replace with silicone hose
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post #5 of 14 (permalink) Old 08-08-2019, 12:18 PM
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Quote:
Originally Posted by RAGoody View Post
..... Can I ask what may have caused this as all fine till about 30 miles in to journey. Where 60mph was 3500rpm it is now 4000 ....
I should have read everything more thoroughly
IACV hoses would normally show at idle

So here's the deal - the ONLY thing that can cause the bike to have higher rpm at the same speed is the clutch - even if the engine was revving higher, then the speed would also be commensurately higher
So if engine speed is higher at the same road speed then clutch is slipping
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post #6 of 14 (permalink) Old 08-08-2019, 02:12 PM Thread Starter
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Quote:
Originally Posted by DEcosse View Post
I should have read everything more thoroughly

IACV hoses would normally show at idle



So here's the deal - the ONLY thing that can cause the bike to have higher rpm at the same speed is the clutch - even if the engine was revving higher, then the speed would also be commensurately higher

So if engine speed is higher at the same road speed then clutch is slipping
Thanks DEcosse, I will have a search on how to cure the clutch slipping. It did have a different turn on the way home as Speedo was correct up to 60 then with a steady throttle the Speedo would show a slowdown but if you accelerated it would speed up but he Speedo would struggle to show past 60 (this was at 70mph).

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post #7 of 14 (permalink) Old 08-08-2019, 07:36 PM
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Quote:
Originally Posted by RAGoody View Post
... Speedo was correct up to 60 then with a steady throttle the Speedo would show a slowdown but if you accelerated it would speed up but he Speedo would struggle to show past 60 (this was at 70mph)....
Sorry - this is getting confusing ......
Are you saying the BIKE was going faster (70mph) but the SPEEDO was not increasing?
Or that the ENGINE was at higher rpm, but speed not increasing? (which was my initial presumption)
If the former, how can you tell the bike was doing 70 - or are you just saying that with the tach indication, you would normally be indicating 70, but it was only at 60 (and not going any higher even though engine rpm increased?)

The most common and simple reason for the clutch slipping is there is no slack in the cable. Back off the adjuster until you get a small free play in the lever before it starts to pull on the cable.
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post #8 of 14 (permalink) Old 08-09-2019, 12:46 AM Thread Starter
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Apologies for not adding below in previous reply.

I placed my Sat Nav on bike for the return journey, all speeds matched till 60 then (not all) the Speedo would drop 5mph, as I then accelerated Sat nav speed reading would rise but bike Speedo would do little, hence speed comparison.

Will have another look Saturday and take out for test as now adjusted cable. Thanks for your help to date.

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post #9 of 14 (permalink) Old 08-09-2019, 11:13 AM
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OK - that is a different animal altogether - if your GPS speed IS increasing, then you don't have a clutch issue
Your bike speedo would normally be as much as 10% FASTER than a GPS, (i.e. if bike was going 70, would typically be indicating 75+) - so definitely an issue with your speed indication

You possibly have a cracked speed sender rotor - have you perchance had front wheel off recently?
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post #10 of 14 (permalink) Old 08-18-2019, 02:28 AM Thread Starter
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Sincerest apologies for not following up on this, been away. Took bike to place I purchased it from yesterday and after the mechanic ripping it apart and some rewiring he finally took the speed sender off the wheel, what a mess, the inner workings of the u it were in about 8 different pieces.

Thanks to DEcosse, absolutely spot on, new part ordered just awaiting delivery.

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