YZF750R- EXUP valve related fault?

[graham247]

Hi everyone



On Sunday was out on my 1998 YZF750R when I noticed the rev counter suddenly flick to 7000rpm then drop to show 0 rpm then a few seconds later ping up to 7000rpm again. The actual engine revs and power remained normal and no other issues apparent. On arriving home let the bike cool down, then turned ignition on. With the engine not running, the rev counter started cycling between 7000rpm and then back to 0 then 7000rpm again etc and repeat.



Had a look on a online few threads noting that the "7000rpm" is a Yamaha diagnostic indication that points to a problem with the Exup system. So tank & fairings off and had a look. Examined the cable ends at the valve and one was badly frayed/rusty/stiff. Said cable has been removed and a new one ordered.



I also removed both cable ends from the servo motor so the servo was free to operate. Then turned the ignition on thinking that the servo motor/pulley would now be free to rotate - which it did and I expected the 7000rpm tacho bounce would not be seen if a seized cable had been the problem.



However...the tacho continued to bounce to 7000rpm back to 0...7000rpm again.



So I though maybe there is a fault with the actual servo motor. I happened to have a spare motor I bought last year, so plugged that into the loom and turned ignition on. The fault remains just as before.



I have checked the electric connections hooking up the Servo to the loom and all are clean and in good condition



Beginning to wonder if the 7000rpm code might indicate some other problem.



Any more ideas or things worth trying please? All info appreciated.


Thank you.

[beardy]

If this type of fault was on my car I’d plug my OBD reader in and read then clear the fault codes. I don’t think you can do that on a bike from that period? But maybe disconnect the battery then reconnect and see what happens. Or when you come to fit the new cables and go for a ride it’ll self right? Good luck 👍🏻

[andy748]

Hi Graham, my mate had a similar issue with his Gsxr, turned out it was the reg/rec going down, the rev counter jumped all over then to zero, make sure yours is charging the battery, easy to check? Andy.

[evochris]

Once reassembled and it’s done it’s checks it should clear, my 98 R1 did the same, new cables and freed up the valve and it never did it again.

[Chewie01]

I have been considering getting a YZF750R and looking through ebay I saw this video linked from one of the ads.
I assume it's showing the same fault code as yours?

[graham247]

Nov 16, 2022 21:47:41 GMT 1 Chewie01 said:

I have been considering getting a YZF750R and looking through ebay I saw this video linked from one of the ads.
I assume it's showing the same fault code as yours?

Hi,
I've had a look at the video - and I would say only "possibly" it's the same issue. The guy twitches the throttle and the tacho jumps to 7,000 and then falls back to idle (but the engine never actually revved to 7,000 that's for sure)
My fault with the engine running at idle and not touching the throttle, has the rev counter jumping to 7000, then back to 0 a few seconds later, then back to 7000 and repeat...So I am not convinced the bike in the video has the same problem. However if you are thinking of buying I would want to see the bike idling and watch the tacho carefully. It shouldn't jump around at idle - if it flicks to 3000 or 7000 rpm then falls to 0 then flicks up again then there is a problam that needs addressing. 

Back to my bike - I have completed further investigations and it appears the root cause is down to the fuel pump and sensor assembly. Looking in the service manual Pins 1 & 3 from the assembly's electrical connector should show continuity (i.e. 0 resistance when checked with a meter.) Unfortunately mine shows open-circuit 100% resistance.

To prove this further I jumpered pins 1 and 3 together on the loom side - and the fault cleared, rev counter returned to acting normally. So although I had one rusty Exup cable, that wasn't the main problem.
Next step is to remove the fuel pump assembly and see if it can be fixed.

As an aside, if you are thinking of getting a YZF750 they are cracking "old-school" superbikes, handle pretty darn well and plenty of power for the road.
Thanks  

        

[graham247]

Hi all,

Just to update, I took the fuel pump and sender unit out of the tank this evening and found the connection had indeed broken from the green wire to the solder joint at the sender unit.

Re-soldered and will put it all back together next week when I've got hold of some shrink wrap.

Thanks for everyone's input and ideas. 

[steve63]

Nov 19, 2022 23:09:11 GMT 1 graham247 said:

Hi all,

Just to update, I took the fuel pump and sender unit out of the tank this evening and found the connection had indeed broken from the green wire to the solder joint at the sender unit.

Re-soldered and will put it all back together next week when I've got hold of some shrink wrap.

Thanks for everyone's input and ideas. 

I have a 1999 R1 and I'm pretty sure my rev counter was doing the same, 7,000 rpm thing. The bike had been stood a while and It felt a bit flat to ride low down so after reading up a bit I stripped the valve, re-fitted it and it went away. That's missing out the bolts shearing, drilling tapping, Copaslip blah, blah bit. I could check the hand book but pretty sure it was 7,000.

It did it again a few years later so I used a different approach, I ignored it and just rode the thing. Within a few miles it sorted it's self out and not done it since.

The guy I bought it off said he had an issue with the valve. He took it straight to a shop and they fitted a new valve (second hand from a race bike that had been changed to a full race system) and charged him £100 for the valve plus a few hours for fitting. Knowing the shop I wouldn't bet against them freeing the original off and taking his easily parted with money.

The thing is both the valve and the bearings or rather sleeves they run in are pretty baggy. I find it difficult to believe they actually seize at all.