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Discussion Starter #1 (Edited)
Ok, so a little back story on the bike. I bought it last summer with 20k miles. Had a very slight hesitation in upper rpms. I check the fuel filter and it was nasty. I put a new one on and it ran perfect. Not long after is when I encountered this problem. Anything over 1/2 throttle, it boggs down. No matter what, it won't go past 5-6k rpms. It just sits there and hesitates, like power-no power-power-no power, but it doesn't gain speed.

I pulled the filter again and it was still clean. Checked the stva by removing it. I took off the stps, which i found out later that I wasn't supposed to. Everything looked fine. Put it all back together and it threw a C28 code. Took it for a spin and it didnt hesitate at all. But when I gave it half or full throttle, it would climb the rpms VERY slowly. I found out that I didn't put the stps on correctly and the butterflies weren't opening fully. I corrected that, FI light went off, witnessed the stva operating on start up, took it for a spin, and same ol hesitation problem. What the deuce goose?? Clogged injectors? Bad pump? Any ideas? Thank ya kindly


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How did you check the fuel filter? It should be attached to the pump, part of the pump assembly. You can also check the fuel output and pressure from the pump on a bench. Mine has proper pressure, but could not reach volume. The bike would bog and not rev past about 9000 rpm.
 

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Friend of mines K6 wont rev past 6000RPM but runs perfectly otherwise.

I bet my arm its a fuel pump pressure/flow issue too. If yours runs well but hits a 'soft' wall (like you roll off the gas) then its definitely a fuel issue. A spark or injector problem would be VERY abrupt & you'd know all about it.
 

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The pump actually has two filters, a strainer-like filter at the inlet and the "real" filter on the outlet. It sounds like the OP may have only checked the strainer. The real filter is expensive and difficult-to-impossible to clean.

A better test, which can be done without pulling the pump, is a flow test. See page 5-7 of the service manual for details but all it involves is connecting power to the pump and measuring the flow rate. As far as I know, it's unnecessarily complicated as it involves pulling a pin from the ECM connector. A simpler version of the same test is shown on 5-5 of the K5/K6 manual. There, the leads to the pump are disconnected and power is applied to the connector pins. I don't know why but the K3/K4 flow spec is more than double that of the K5/K6 spec, which seems too low for the bike's horsepower. Take care that you don't slop gas all over things.
 

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Discussion Starter #7
Well that was my next question. How can I tell if the pump is bad, or if the filter assembly is bad? Since the filter is so expensive, I might as well go for a used fuel pump. So either way, bad pump or clogged filter, I might buy a used pump.

Checking the flow rate sounds a little complicated. I don't have any tools to do that. I've taken that damn pump out so many times it literally takes me about 10-15 min to get it out. So it's not that big of a deal. I'll take it to someone and have them check it out.


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Discussion Starter #8
I found an 03 750 fuel pump that's local, it looks damn near identical to mine. Will that work? I can't find a concrete answer on the net. Only differences I can see is the 750 doesn't have a wire coming off the thermistor like mine and the 750 has 3 grounds and mine has 2.


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Discussion Starter #9
Ok, so I bought that used pump that was from a wrecked 03 750 w/ 4k miles. I only used the actual silver pump and this silver filter, not the mesh filter. That was the only way I could make it fit. Took it for a test spin. A LOT faster...however, only if u apply less than half throttle, and stay below 9k rpms. If u give it more than half throttle...hesitation...if u try to go past 9k rpms...hesitation. Although its not as bad as the hesitation before.

The only parts I reused on my pump were the thermistor and the black plastic housing, whatever that is. Am I looking at cleaning my injectors now??


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Bigger engine needs more fuel so the flow rate needs to be bumped up at the same pressure so the 750 pump would logically not do the biz at high flow rates.

Seems you need a 1000cc bike pump mate...
 

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Discussion Starter #12
I'm pulling my injectors tonight and getting them professionally cleaned tomorrow. I'll have them back and in the bike Thursday night. I'll let y'all know if this fixes my issues.


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Discussion Starter #13
If my fuel rail is any sign of how dirty my injectors are, they need a good cleaning. There is a bunch of gunk on the bottom of my butterfly blades, so I'm gonna get the throttle bodies nice and clean while my injectors are getting flushed.


ImageUploadedByMO Free1368587774.314691.jpg ImageUploadedByMO Free1368587786.638436.jpg ImageUploadedByMO Free1368587798.588508.jpg


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Discussion Starter #14
UPDATE...got my injectors ultrasonic cleaned today. All ended up flowing 26.25 lb/hr. I cleaned the fuel rail while I was in there. I put everything back together and went for a spin. Now it doesn't hesitate at full throttle...until I hit 7k rpms, then it starts to hesitate. If I let off the throttle a little, it will climb to 9k or 10k rpms and that's it. I'm stumped. I even unplugged my power commander lll to see if that would do anything...no difference. The only variable is the used pump and fuel pressure regulator or filter, whatever that little silver piece is that has an inlet and outlet w/ O-ring

Any suggestions on what to try next?


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Discussion Starter #15
What is this black housing that is part of the fuel pump? This was from the 750 pump, I didn't use it because I would have had to use the 750 thermistor, which longer and had 2 wires, while mine was shorter with only one wire. Is this what could be causing my hesitation?


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Discussion Starter #16
Ok, so after further research, I found that the black plastic housing does contain the filter. I'm betting this is why I'm still having the hesitation issues. I want to use the 750 filter, but if I do, I'll have to use the 750 thermistor. If I do that, I will have 3 wires to connect to the fuel pump housing. However, my 04 1k fuel pump housing only has room for 2 connections. I don't know shit about wiring, or electrical stuff, but could I piggy back those two thermistor connections onto one mount? Or would that fry something? That would be the only way I could use it, unless I just cut that 2nd thermistor off


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According to Ron Ayers where used part number finder the K3 750 pump is the same part used in the GSX-R600 and GSX-R1000 (and other models) for 2003 and 2004.

You could leave the thermistor unconnected and give the filter a try to see how it goes first up. If it fixes the problem start trying to make the thermistor work.
 

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Discussion Starter #19
UPDATE!!!!!!! Replaced my black plastic filter housing with the used 03 750's, along with the thermistor. Although it has one more thermistor connection, I just left it disconnected. I know my low fuel light works cuz it just lit up.

Bike runs absolutely amazing. I forgot how fast the liter bikes were. This thing hasn't ran right in the year that I've owned it. I couldn't be happier right now. I'm about to go seafoam the bike to clean up the valves. I took some before pics and I will take some after pics as well. I might do a separate thread to show how clean they got.

Thanks for the help gixxer.com


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The filters clog up quicker than you would imagine and they start to run marginal. The injectors work better when they are getting 3 bar full pressure. Even at low revs believe it or not.
 
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