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Fueling issues.

4K views 83 replies 8 participants last post by  Leooo 
#1 ·
Hi guys, I just purchased a 2009 750 with only 8200km on the clock! I took it for a short test ride before I bought it and it seemed to run sweet.

I took it for a longer ride today and it seems like there is some problems. I went to overtake a car and when I hit about 9000rpm it would stop revving. Also at partial throttle the felt quite jerky at low rpm. It also stalled at idle a lot. But at full throttle through the midrange it ran sweet.



I have a feeling the bike was sitting for some time. My suspicion is that the injectors are gunked up..especially the secondary ones. That and a weak spark from the plugs. I'm not sure though.

Does anyone have any expirience with my situation? It has aftermarket Yoshimura headers and an r55 tip..no power commander.

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#4 ·
No, no FI light. Each time I tried to Rev it it felt like it would clear up a tiny bit and Rev a bit more hence why I think it had blocked injectors. It has that distinct feeling of being starved of fuel and i think about around 9000 rpm is when the secondary injectors kick in?







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#8 ·
Being that is has the cat removed, it would behoove you to add a power commander and have it tuned. But, this is after you have your issue fixed.

If you just purchased it and have no history of its maintenance, you should assume it was not done and take care of it. I don't know what your manual calls for at such low mileage, so look in the service manual and take care of it. It does sound like gas may be a factor. You should drain the tank and refill it with fresh fuel, making sure to note if there is rust in the tank. After this, you can run it for a bit and see if it clears up. There are already detergents in top-tier fuels, so it may clear it up. If you've already been riding it with fresh fuel and the problem remains, you should do a fuel flow test as outlined in the Service Manual. It's free and it will tell you if the fuel pump and filter assembly are to blame.
After that, you can look at the spark plugs and the injectors. But, a proper cleaning is not cheap for those. It's around $12-20 an injector, and you have 8 of them.
 
#9 ·
It was serviced less than 1000km ago...never seen oil so clean in an engine ha. The thing was ridden less than 1000km a year and I don't know if fuel was sitting in it untreated.

I'll have to look up how to do test the fuel flow. I hate working on a new bike though because I'm clumsy as shit and don't wanna scratch it haha. Also don't wanna piss money in a new bike having a mechanic do these time consuming things.

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#10 · (Edited)
I was riding it today in the mountains and I entered a turn not super aggressively but a decent pace and as soon as I touched the throttle the back spun up and kicked out and through me out of the seat...needless to say I changed my pants after...very lucky save.

He said the tyres are with in 12 months old... with less than 100km on them. pirelli angel gts...look pretty new..still had the gt in the tread. So I hope it was just that they needed to be worn in and not that they are old and dried out.... they are dated 10/ 2015...and fitted one year ago...are they OK to run?

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#11 ·
I was riding it today in the mountains and I entered a turn not super aggressively but a decent pace and as soon as I touched the throttle the back spun up and kicked out and through me out of the seat...needless to say I changed my pants after...very lucky save.

He said the tyres are with in 12 months old...pirelli angel gts...look pretty new..still had the gt in the tread. So I hope it was just that they needed to be worn in and not that they are old and dried out....

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If you didn't know, you can actually tell when the tire was made.

https://www.tirebuyer.com/education/how-to-determine-the-age-of-your-tires

If the tires are that new, there are other factors to consider such as the environment and rider input to take into consideration.
 
#15 ·
At around 3 or 4k rpm give or take. I was on a twisty road behind a car in like 3rd or 4th...just maintaining speed or slightly accelerating through a corner..it felt like it wasn't getting a concistent flow of fuel and a bit jerky. When it's and idling the revs jumped up and do below 1000rpm sometimes and it stalls.

This isn't the first 750 I've had and I wasn't lugging the engine

Engine feels great otherwise up to 9000rpm when I get there if I roll back a bit on the throttle it accelerates but not much more.

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#19 ·
Haha I'm getting started now, I had a look at the workshop manual. Think I'll need to go to the hardware store and get some electrical wire and I'll need to get a bit of hose to run the fuel out of

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#23 ·
The exhaust valve has been removed as its not a stock header. I'll try changing it back to stock. I'm not sure where to look next. I hope it's an easy fix, I just bought the bike and don't think I'll get the money back ; (

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#29 ·
No, I haven't yet. Just woken up here in Australia haha. I'm going to do that, but also was wondering if anyone has had any similar problems and what they did.

My problem persists at idle as well as when you get to high rpm. If it was a fuel issue it wouldn't effect it at idle so much? If I blip the throttle in neutral the revs don't hang.

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#28 ·
You can temporarily bypass the kickstand switch, that is another free test to rule out a potential problem. It still sounds like something with combustion, though. Check the spark plugs and the air filter. You can also do a compression test while you're doing the spark plugs.
 
#31 ·
You're so right man ha. The other night I couldn't sleep because I couldn't wait to ride the thing. Now I can sleep because I can't wait to fix the thing.

Motorcycle ownership can be an emotional Rollercoaster at the best of times. I don't thinks it's an expensive fix but it may be tricky to find. Got to do a vehicle inspection on it today so I'll see if my mechanic mate has some advice too.

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#33 ·
After you check and/or replace the spark plugs and check the air filter for any clogging, you can eventually move on to pulling all 8 fuel injectors and do a DIY cleaning. But, that's after you do the easy stuff.
 
#35 ·
Bike only has 8200km on the clock. There was still half a tank of gas when I got it that I didn't drain, I just topped it up with fresh gas. Then looking through the service history I found this thing has only been ridden 100km in nearly a year.

He rode it to my house so I assumed it was all ok. From what I can tell it sounds like he never road it hard or revved. He barely road it ha!

I'll drain the gas and check the plugs and filter. Could it just be bad gas? Let's hope it's that simple. It could just need to err..'clear it's throa't after sitting haha

I get the bike back later, still sorting the registration.

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#38 · (Edited)
Hey guys quick update, I went ahead and changed the spark plugs, they looked pretty black. It now idles at a consistent rpm and shows no signs of stalling

Sadly it's raining and the roads are wet. Don't wanna get crap flicked up on the my new bike. Going to drain the gas tomorrow and fill up a fresh tank.

Fingers crossed it runs good.
Cheers guys!

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#39 ·
Hey guyz, just taken it out this morning for a ride. 8t runs a lot smoother and doesn't stall after changing the plugs.

It still stops accelerating after 8000rpm...if I roll back to about %80 throttle it jumps forward like nothing is wrong.

Any ideas what might be giving me the trouble? Fresh gas, plugs and furl flow test checks out.

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#42 ·
I was talking to my mechanic today and he said even if I got the correct flow rate when testing it it's most likely pressure related and once you hit about 8000rpm the pressure drops and yoy wont get enough fuel.. I'm going to see if I can borrow the pump out of my friends 750 and then I'll know for sure.

Otherwise next step is tps and then check the stva and then pull the injectors.

Other than that the bike is sweet, only time it bothers me if is I'm trying to get round a car in a hurry.

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#44 ·
Hey guys, a quick question. If it turns out my pump is bad, is it possible to just replace the motor in it? Would that be what is faulty or is it a sensor?
Depends on how you know your pump to be faulty. If the flow rate is inadequate, but the voltage on the pump's terminals is ok, most likely you have a clogged high pressure filter, a clogged strainer, or both. If the pressure is inadequate, you probably have a leak somewhere inside the pump assembly (assuming that you'd see the pool of fuel under the bike and/or fire caused by an external leak). If you just swapped the pump with another and your problem went away, any of the above is possible.
 
#46 ·
I can't imagine how the pump motor would somehow keep working but not build enough pressure (again assuming proper voltage, which I think, the ECU monitors). I also think that a leak-induced pressure loss would be worse at lower rpms (well at lower loads, but engine speed is part of that). So, assuming that your motor stops accelerating at higher rpms and that the flow rate is fine (but post your results and testing methodology anyway to make sure), I'd be leaning towards clogged injectors, or perhaps a kinked fuel line.

This has come up before, but I don't remember the history of the thread. Has this been checked? Also, when the engine stops accelerating, does it happen smoothly, as if you hit a false top speed? Does it perhaps do so more violently, as if you loose spark from a rev limiter say? Finally, is the rpm limit fixed, or can you accelerate past 9000rpm with less throttle, and not even reach that under WOT?
 
#47 · (Edited)
Hey thanks for your reply! I tested the flow rate by hooking a tube up to the fuel line then hooking the pump up to the battery. I let it flow for 30 seconds exactly and got 1200ml. It's not like a rev limiter...once I get to 8000rpm it's like there is significant power drop off...it will accelerate but very slowly. It feels like when you go from A mode to C mode at full throttle but more extreme. If you you roll back to %80 throttle it will pull like there is no problems all the way to like 12,000rpm. It has a similar feel to running out of fuel without the sputtering.

Everything in there is clean and I have new plugs. I couldn't imagine it being injectors. My mechanic said the only time he's seen someone with my problem it was the fuel pump :/. This sucks because I was suppose to go cross country on the bike soon

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#50 ·
The mechanic down at the local Suzuki dealer, they're good guys. He said the only time he's seen a gsxr not being able to get over a certain rpm it was due to a fuel pump gone bad. It's not a very big town though.

I haven't checked yet because I haven't worked on injectors before. I've got a workshop manual and a whole weekend, so I'll sit down and do some research. I've heard you can swap the connectors on the injectors so the ones that would be firing as secondary now run a primarys, would be a good way to diagnose if it the injectors?

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#51 ·
You still need to check fuel pressure, to make sure it's at the proper PSI. You verified the flow, which was right at the specification, so I don't imagine it's your pump. It could be a fuel line that is kinking when you lower the tank, or possibly injectors.
The problem I see with swapping injector connectors is that by doing so, you run into the issue that your secondaries are going to be spraying when the secondary butterflies are not all the way open, which might cause issues with how it runs.
 
#52 · (Edited)
Thanks for your help bud. On my to do list tomorrow is take out the fuel pump and check the filters and stuff for good measure. then inspect the injectors.

I'd love to check the psi but I don't have a pressure gauge and I'm moving soon so any tools I buy will be a waste :(. Hopefully the mechanic down the road will let me use one. I was going to ride my bike 3000km south to my mums house and store it while I got to Vietnam and do a motorcycle trip there!!!! Tempting to just ride it down there anyway and worry about it when I get back. I really want to do this trip with %100 power though ha

I was riding it today and it nearly pulled to redline in 1st and 2nd...I've owned the same 750 before and there is a definite power drop, so maybe the more I ride the more it clears up...it's only speculation though. It's hard to test because pretty much breaking the speed limit so I have to drive out of town each time I test...

It came with a spare battery and I get the issues with that....I'll check my fuel line and make sure isn't twisted or kinked in any way.


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