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Discussion Starter #1
05 650, 85k miles/136k k’s
Cleaned the tank and installed New fuel pump ( because it needed a new fuel pump, not because I thought it would fix this issue, this wasn’t an issue yet) and it ran perfect for 500miles/ 800k’s
Now it starts to hesitate and stutter around 5500-6000rpms, and gets worse at lower rpms as I continue,
By the time I got home 4300 rpms was the bests it would do. Any ideas where to start looking?
please explain things like your talking to a 10 year old. This is my very first bike and I’m still learning the lingo!
PS clever stabs and insults are welcomed, just make sure they don’t suck! 👍
 

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Well how did you determine it needed a new pump and what exactly did you replace? The whole pump assembly (including pressure regulator and filter) or just the pump itself?

The symptoms fit a progressively blocked high pressure fuel filter (the one that is integral inside the pump assembly).
 

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Well how did you determine it needed a new pump and what exactly did you replace? The whole pump assembly (including pressure regulator and filter) or just the pump itself?

The symptoms fit a progressively blocked high pressure fuel filter (the one that is integral inside the pump assembly).
Pitiful flow rate, it would rev to 5k and fall suddenly
 

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Pitiful flow rate, it would rev to 5k and fall suddenly
That's also a symptom of blocked filters, the high pressure one in particular.
 

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I had a car that would not rev past a certain rpm, in any gear. Sometimes it did a little better, sometimes worse. Drove around like this for months (Sometimes only able to do 30mph uphill) until I figured out that the $5 fuel filter was clogged. Fuel flow and rpm are pretty closely related.
 

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Sounds just like my v2, there was nothing wrong with the pump just bad fuel.
 
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Do a fuel flow test Quick fuel pump flow test. to confirm any blockage. If out is within spec, then as Rolex suggested, look for fuel contamination. For the contamination test, use the fuel that was collected for the fuel flow test.
 

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please explain things like your talking to a 10 year old.
I agree with all the others. It's most likely a blocked high pressure filter.

Here's a quick test that you can try and do. With the gear in Neutral and the engine running, see if you can rev the engine to the point where it starts hesitating. Most likely in neutral you can rev the bike all the way to redline without any issues. Then try to do the same thing in 1st, 2nd and so forth. You will most likely find that the hesitation occurs at a lower RPM with the higher gears.

What you can also try is to put the bike in, say, 3rd gear, and quickly (full throttle) try to accelerate to redline, and then try this test again but slowly (half throttle) accelerate. With the quick acceleration the hesitation will most likely appear earlier than with the slow acceleration.

If these tests all check out, then the issue is definitely related to a restriction of the max fuel flow. The pump pressurises the fuel and then filters it through a fine-mesh filter. If this filter becomes clogged - and it will, eventually - this restricts the flow rate. When the engine has low power demands the fuel flow rate is sufficient, but when the engine requires more power (when accelerating hard, or when cruising at high speed) there's now insufficient fuel.

This is made worse by the way the engine sensors work. Your ECU has manifold air temperature/pressure sensors, a throttle position sensor and a crankcase speed sensor. From this the ECU is able to work out how much air is in the throttle bodies, and from there how much air gets into the cylinders. It also knows the (design) pressure of the fuel rail, so it can open up the injectors for a certain duration to inject fuel into the throttle bodies. If everything is running perfectly, this should lead to the right, 'stoichiometric' ratio between fuel and air for optimum combustion. But the engine is not able to measure directly if it is actually achieving that ratio - all the measuring is done indirectly.

(In fact, the measuring is only done on one cylinder, and the assumption is that the other cylinder is adjusted properly so that the same parameters apply there as well. That's why a Throttle Body Sync is so important.)

So if either the fuel pressure in the fuel rail, or the manifold air pressure (the air pressure in the throttle bodies) is off, then the fuel/air ratio is wrong. And gasoline only has a relatively narrow band where proper combustion will actually occur. Outside that band, especially on the "lean" side of optimum (not enough fuel for the air that is present) combustion stops pretty quickly. (The "rich" side of optimum is actually a lot more tolerant.) This is why the onset of that stumbling is so rapid.

The real, proper way to test whether this is truly the case is to attach a pressure sensor to the fuel rail and see if it maintains the proper pressure throughout the full RPM/load range of the engine. However this is pretty hard to do if you don't have the proper equipment and a dyno. But since we know that a fairly common issue is the clogging of the high pressure filter, your service manual contains a "fuel flow test". You attach a hose to the fuel outlet of the tank, apply direct 12V to the pump for 30 seconds, and measure the output. And if that fuel flow test is too cumbersome to execute, people on this forum have developed a "quick fuel flow test" as well. Again, you attach a hose to the fuel output but instead of applying 12V directly to the pump, you just cycle the ignition three times, then measure the output. The previous posts contain the links.

Once you've confirmed a fuel flow issue, you need to fix it. First, you need to understand that there's actually two filters in your bike. From the tank the fuel first passes through a coarse "strainer". This is the mesh thingy that sits at the bottom of the tank right there where that last drop of fuel gravitates to. This strainer only filters out the larger particles, the ones that would clog the pump. After this strainer the fuel is pressurised by the fuel pump, and then it passes through a second, fine filter. This second filter - commonly called the high pressure filter - is to filter out the particles that would clog the injectors. And this filter is integral to the pump: It cannot be replaced separately. It's this internal filter that normally causes a problem.

To change this internal filter you need to change essentially the whole pump assembly, which is a costly affair. That's why some clever people on here developed a "bypass" procedure. You drill a hole strategically in the pump so that the fuel can bypass the clogged filter. You then put a regular, automotive, fuel filter into the fuel line between the pump and the engine. This fuel filter has a significantly bigger surface area so it doesn't clog up as fast, and to change it requires loosening two screws and a new, $10 filter.

The fuel filter bypass will cost maybe 20 dollar in parts, and takes about an hour and a half to execute if you're well prepared. Most of that time is spent gaining access: Removing the tupperware, tank, airbox. Preparing the new fuel line (can't reuse the existing as it's plastic), filter and connectors is 10 minutes, and drilling the hole in the pump is another 5 minutes (4:30 minutes measuring, 30 seconds drilling).
 

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We should refer to this write-up on future "hesitation at 5k" issues. My only comment is that some newer versions of the pump assembly do allow to change the high pressure fuel filter (FILTER Part # 15310-17K00). Not sure from what year onward.
A lot of threads about the high pressure filter bypass. Best to do a Google search .
 

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Discussion Starter #11
Well I decided to just pull it off and look at it. It looks like I did a real shitty job of cleaning out the tank when I put the new OEM fuel pump assembly in. Looks like a good flush maybe all it needs. But I’d still like a pro’s opinion.
I’ll have to do a better job of cleaning the tank this time,
Clean the pump and filter. And maybe do the bypass a lot of people talk about.
Thanks for all your help and ideas. Hopefully my Wee will be back up and Roaring soon.
PS is there a “better/ best” way to clean this tank?
 

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Looks like a good flush maybe all it needs.
Some people have reported (temporary) success with back flushing the pump, where you put pressurized fuel in the outlet side of the pump to flush the debris back out via the inlet side. Never did this myself, and I don't know if there's any check valves or anything that you might need to override.

Given that the fuel bypass mod is so simple to implement, I would go for that instead.
 

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You can apparently run the pump backwards by reversing the polarity. That has been reported as a means to (temporarily??) help the filter blockage. Worth trying if you are on a trip and get stranded. Bypass is the way to fix the problem for good.
 

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I have a couple of bush basher cars down the farm that require the pumps be run backwards every now and then, I have never tried it on a Strom.
 

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It probably is a clogged filter as others have said, but I'd throw some new fuel in it just in case there's a cheap/easy solution. Once met a guy in BC randomly, and rode to Alaska with him. We got fuel in a small station on highway 20, I got regular and he got premium. 20 miles later his bike wouldn't go past 4K, and wouldn't idle. We eventually determined the gas was bad (seemed to have water in it). It''s probably the high pressure filter, but I'd swap the gas first.
 
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