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Discussion Starter #1
Hello everyone, been away from the forum for years, kid got crook so I gave the bikes away. She is quite the young lady these days so all good there now.

Ive owned several Gixxers, K4750, K41000, 2xK51000

Ive had another K41000 for the last 6 months.
It was in pretty bad shape when I bought it, mostly cosmetic, slowly been bringing it back to its former glory. Its got 55000K's on it, Ive put 7000 of those on the clock and until this last weekend it has been as strong as an ox (performance wise)

Put 1800ks on it this weekend at a place we call the snowy mountains, arguably the best riding place here in Australia, altitude is only about 1200mtrs so that shouldn't be an issue.

The bike developed a problem on the weekend. It revs freely to about 6000, bogs down to about 8 and then FULL Power is back, whack.

I'm aware the fuel pumps, and filters can cause issues with these bikes in that they can bog down WOT but Ive never really heard of a fuel pump/filter to rev then bog at mid range and the get going again between say 8000-12000.
In saying that the issue occurred only this weekend I did notice in the last week to 10 days that is didn't bog mid range but it defiantly feel like it really got going up around 10k and it was noticeable, I could feel a surge in power.

I haven't done a fuel flow test yet but I have ordered a new pump/filter assembly, I sought of figure Ive come this far with the bike I may as well do the pump because if it is not the culprit causing the bogging it must be pretty close to needing to be replaced anyway.

Am I on the right track with the pump/filter or could there be anything more sinister causing the bogging?

Anyway, good to be back on the forum and than to Yung with the password help. :cheers
 

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I know things... A lot of things.
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If the engine produces full power above 8000 rpm, then I can't see how it can be the fuel pump or filter. At any rate, replacing the pump without a flow test is generally not advisable as the OEM unit is an unnecessary expense if the existing part is fine and any much cheaper aftermarket replacement parts are likely to be substantially worse than the OEM part they'll replace, even if they're new.

So how exactly does it bog down after 6000 rpm while still managing to climb to 8000 rpm? I can't imagine anything that would cause such an issue, without throwing a code. Do you see FI flashing on the dash? If not, I could only advise trying to run with the IAP sensor disconnected, to see if it'll help and inspecting the plugs. The former might conceivably cause problems at lower loads, which are then resolved when the ECU switches to Alpha-N fueling at higher loads. The latter, might conceivably fail to ignite the mixture properly if worn and perhaps the mixture between 6-8000 rpm is a bit off, due to an aftermarket exhaust setup or some similar issue.

Both are a stretch though. The issue will likely prove to be something simpler.
 

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Discussion Starter #3
Thanks for the reply...
At about 6k it almost feels like it is hitting the limiter for a second or 2 but the revs continue to climb but slowly by holding the throttle open, the power deliver is no longer linear, it hesitates until it gets to 8000-9000 rpm, and when the power returns it is instant and it launches itself....
No FI Fault and no code thrown.
It does have an A/M exhaust on it but absolutely no sign of bogging in the previous 5000k's, power delivery has been linear and plentiful up to this point.
Other than the exhaust the bike is stock.

I agree that it is not good practice to just change the pump/filter but it will eliminate that being a possible cause and I did get a good price.
 

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Even in purely diagnostic terms, a fuel flow test is easier to perform, has less chance of causing more issues and complications and is more conclusive than swapping the whole pump assembly.
 

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Discussion Starter #5
I haven't swapped the pump yet, will do it this weekend.
I took the bike to a quite, straight, 1200mtr road near mine tonight and wound it up to 11000 in 1st, 2nd and 3rd and couldn't replicate the problem, power was linear all the way through the rev range, front wheel bouncing on the surface in 3rd.
I noticed the TPS line next to C00 was in the middle on fast idle and went to the bottom when warm so it need adjusting but I doubt that is causing it.

I might be barking up the wrong tree
But
I suspect the big miles I put on the bike last weekend stressed a failing pump.
Something I noticed tonight whilst idling there was a very high pitched sound coming from the vicinity of the airbox so when I change the pump I hope like buggery that sound vanishes because that will just about confirm my suspicions.
The only other way would be to go back to the snowys :banana


Intermittent problems, don't you love them.
 

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Unless your new pump is brand new, including the filter, you need to do the flow test. I gather that a new pump is around $800 AUD - pricey. Pump motors can fail but unless they're all rusted up, they're probably OK. Furthermore if the existing pump was bad, all you probably needed was the filter, which is half that.

A high pitched sound from the vicinity of the airbox could be many things, including the timing chain or valves.

The first thing to test is the flow rate. However your symptoms sound like something else. You say the exhaust isn't stock. Was the EXCVA removed? If not, it could be sticking so as to cork things up and then opening. Beyond that the secondary throttles might not be opening properly due to malfunctions of the actuator or the sensor. You could disconnect the sensor and look at the resistance between the Y and B leads. It should vary smoothly without any dead zones as the throttle valve is rotated. See 4-48 in the service manual. While you're there, you might as well check the Bl to Y resistance in the same way. If the sensor is OK, you could check the actuator. Try closing it by hand and then watch it when you turn the ignition on. Page 4-45 indicates that it should open fully (I think) and then close slightly.
 

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Discussion Starter #7
Yeah, brand new pump.
I got plugs oil and filter and the dealer gave me a good deal, 800 list for the pump but got the lot for 750AUD.

I didn't bother with a fuel flow test, bolted the new pump in, changed the plugs, cleaned the air filter.

Took it for a run and the difference is night and day, throttle response is crisp as, from just off idle the power delivery is silky smooth, drive out of corners is, well, quite astonishing.

One of my sons has got a K6, he knows the bike, he took it for a run and came back giggling, all he had to say was you had better fix that steering damper real quick :grin2:

I am astounded that a bike with 55000K's on it can feel so good.
I dont know if it was the pump or the plugs that have made it so responsive nor do I have any idea if the initial problem will return but for sure the bike is worth persevering with.
I bought the bike for 3k 8000K's ago, I only wish the knob I bought it off could feel it now. cost some money to get it this far but by christ its been fun :cheers
 
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