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Gord
Test Rider
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Joined: 21 May 2012
Posts: 328
Location: Teesside
PostPosted: Tue Jun 14, 2022 7:28 am    Post subject: Bike won’t rev over 4,000rpm - suspect EXUP motor Reply with quote

We set off for a 4 day tour of Scotland on Friday and I had to leave my bike behind and carry on the trip on a mates bike.
It has previously done this, however it wasn’t very often and it was easily re-set with a quick flick of the kill switch.
The fault is: the bike will be fine then suddenly not rev over 4k rpm, it’s like it has an electronic rev limiter. I’m aware that if you remove the wires from the EXUP motor, this will have the same effect.
On our trip, right from the off it was happening pretty much non stop. It would hit a rev limit, reset the kill switch then it was ok, a couple of hundred yards down the road it happens again.
We checked the connections at the road side but could not find anything wrong.
I’ve ordered an EXUP motor from EBay, so I will fit that and see if it makes any difference.
The cables are quite new, the valve moves freely, this on a YZF750.
Has anybody has any experience of this fault?
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Stig
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Joined: 28 Sep 2005
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PostPosted: Tue Jun 14, 2022 11:04 am    Post subject: Reply with quote

With ignition off turn servo pulley in either direction. Turn power on and it should reset to centre. Try it both ways
If it resets then servo is ok
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creedxup
Parts department
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Joined: 14 Oct 2005
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Location: hastings sussex
PostPosted: Tue Jun 14, 2022 1:46 pm    Post subject: Reply with quote

The EXUP valve is probably seized in the exhaust and will need to be disassembled, cleaned and greased, if the valve is seized it will cause the servo to limit the revs to 4000rpm

Having a seized valve may or may not cause damage to the plastic gears in the servo, as you have one coming, it’s best to replace it anyway.
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bunk
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Joined: 04 Aug 2021
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Location: Seattle
PostPosted: Tue Jun 14, 2022 4:22 pm    Post subject: Reply with quote

Does the exup do anything by 4 grand?

Im far more aware of when 2t exh valves do work, my fazer you cant tell at all when the exup is doing work.
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Stig
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PostPosted: Tue Jun 14, 2022 6:12 pm    Post subject: Reply with quote

bunk wrote:
Does the exup do anything by 4 grand?

Im far more aware of when 2t exh valves do work, my fazer you cant tell at all when the exup is doing work.


By 4grand the valve should have opened all the way from closed… basically making it a full bore open pipe
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bunk
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PostPosted: Wed Jun 15, 2022 2:44 pm    Post subject: Reply with quote

Stig wrote:
bunk wrote:
Does the exup do anything by 4 grand?

Im far more aware of when 2t exh valves do work, my fazer you cant tell at all when the exup is doing work.


By 4grand the valve should have opened all the way from closed… basically making it a full bore open pipe


Thats good to know !
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Gord
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Joined: 21 May 2012
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Location: Teesside
PostPosted: Sat Jun 18, 2022 7:32 pm    Post subject: Reply with quote

I changed the EXUP motor and also noticed that the EXUP valve didn't turn as freely as it should have.
I stripped it, cleaned it and put it back together and took it for a test run, it appears to be running fine now.
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