Fuel starvation mystery when tank low

[maxtog]

I believe somewhere on the forums, or in the Cog tech pages is a mod you can do to your gas cap so you don't need to use the key to close it.

Yep, I did that mod and posted detailed instructions (it was Fred Harmon's discovery).  But when I replaced the cap with a new one, I didn't do it that time.  I probably should have

http://zggtr.org/index.php?topic=20069.0
Photos were lost, so reposted them further down: http://zggtr.org/index.php?topic=20069.msg313558#msg313558

[maxtog]

And the mystery continues.

I saw IsoHeat at Walmart, so I bought it.  Put in 1/2 bottle on next fill on 12-01-2024....

It did it again today!  At 190 miles into the IsoHeat tank, I started noticing slight hesitation on hard acceleration.  At 200 miles I hit actual fuel starvation issues and some light kicking on acceleration.  At 211 miles it hit reserve/low fuel (which is about normal) but then even moderate acceleration would cause problems.  Filled tank at 217 miles with 4.7 gal + remaining 1/2 bottle of IsoHeat (meaning there was still 1.4 gal in the tank). 46MPG, which is normal.  Pulled out and problem was immediately and completely gone again.

This makes no sense.

[Freddy]

Pulled out and problem was immediately and completely gone again.........until fuel level gets low again.

Replace the fuel pump suction filter.

[VirginiaJim]

I can recall having a similar issue and Freddy is right.  Replace the filter or pump...wait a minute here.. I think I may have something on the shelf.  I seem to recall rebuilding a pump some years back.  I'll take a look and let you know..

[VirginiaJim]

Does anyone know if the 2008 fuel pumps are interchangeable with the gen 2 bikes?

[Freddy]

Yes and yes - ZX14 too except for the first 2 years of the ZX production.

[maxtog]

Well, the problem was gradually getting worse.  Starvation was starting to happen with even less mileage on a tank at high load/throttle (started at 200 miles, now noticeable at even 150 miles).  So between that and the forks leaking, I FINALLY took it in to a local shop for service two days ago.  They called this morning saying they sucked out gas to just half tank (which would be like 125 miles driven) and easily replicated/confirmed the problem exists and asked permission to put it on a dyno for more troubleshooting (apparently adding an hour labor to a yet unknown bill).  So now I wait for news...

Sigh, tomorrow looks like PERFECT bike-riding weather.

[gPink]

Max did you replace the pump filtet?

[maxtog]

Max did you replace the pump filtet?

I am not able to do the fork seals, and they starting leaking like crazy again, so I had to take the bike in.  It seems they leak much worse when the weather is not cold.  Last time I investigated with the shop, they said they were several WEEKS behind.  So there was no sense leaving it with them.  And then the weather changed to cold and the leaking stopped, and so I procrastinated again.  I just threw the fuel starvation problem at them as well (what the hell) since they will have the bike and I would be without it, anyway.

They called and said their diagnosis after testing is that the fuel pump would not produce the correct pressure and has to be replaced (no mention of the "filter" pad being the issue).  I authorized it, but the part will take "7 to 10 working days", so now I have to sit and wait weeks

My problem with this, is that even if the pump were defective, as we discussed before, it should not matter the level of fuel in the tank.  And yet that greatly affects when the problem occurs.  So this diagnosis/solution doesn't explain that behavior.   But, I give up- they are the experts.  I guess we shall see.  Eventually....

[Freddy]

Experts? Money grabbers I'd say since they want you money to run it in their dyno.

The common experience of blocked suction screen is that it is worse as fuel level drops. This has been documented for 15 years or so.

[Boomer]

The problem that the shop has is that Kawasaki only sell the pump for the C14, not any of the sub-assemblies (filters, o-rings, screens, etc.).
All of those parts that we use in our pumps when we DIY are for other vehicles even if they do fit the C14.
It could be the screen, or it could be a weak pump motor, or seizing bearings in the motor, or any one of 50 different things.
As with most modern vehicles the "solution" is to replace the suspected failing part and if that fixes the problem, move on to the next job.

The air-con compressor on my car has stopped compressing and I KNOW that the cause of the fault is the electronics in the compressor, but nobody will look at that. They only want to replace the compressor at great expense to me. Pretty much nobody troubleshoots down to component level these days as it is mostly cheaper to replace the whole unit than to take the time (time is money!) to troubleshoot the actual cause.

[maxtog]

The problem that the shop has is that Kawasaki only sell the pump for the C14, not any of the sub-assemblies (filters, o-rings, screens, etc.).

While that is true, this independent shop (Precision) said it was the pump only and they offered a non-OEM which would be just the pump (disassemble the Kawasaki pump assembly and replace just the pump part).  So it wasn't that they required me to replace it all.  I opted for that, paying more to get the whole assembly.

All of those parts that we use in our pumps when we DIY are for other vehicles even if they do fit the C14.
It could be the screen, or it could be a weak pump motor, or seizing bearings in the motor, or any one of 50 different things.
As with most modern vehicles the "solution" is to replace the suspected failing part and if that fixes the problem, move on to the next job.

Can't argue there.  It is the same with a lot of products now.  They won't sell any sub-part, just "assemblies" and often they are outrageously expensive.

[maxtog]

Experts?

Compared to me, for sure

Money grabbers I'd say since they want you money to run it in their dyno.

Perhaps, but I ran it by my master mechanic friend and he said what they did wasn't unreasonable.

The common experience of blocked suction screen is that it is worse as fuel level drops. This has been documented for 15 years or so.

I agree that the screen/pad is the most common problem when there are fuel delivery issues (that or the gas cap vent malfunctioning, which is the first thing they checked).  But nobody has explained to me a theory as to how the screen/pad can be the problem when the symptom is that the problem only occurs when the tank is more than half empty and gets worse as the level gets lower.  The weight of the gas in the tank is insignificant compared to the amount of pressure the pump has to make.  So if the screen is clogged, it should be clogged all the time, right?

Of course, as I said earlier, I don't know how it could be the pump in such situations, either.

[Pilgrim]

Head pressure varies with the height or depth of the liquid.  But what do I know. 

Glad you got your bike fixed Max, go out and enjoy it. 

[zrx mitch]

There is now a filter/o-ring kit available    99999-0521

[Boomer]

Glad to see that they finally added the C14 & ZX14 to the list for the filter/o-ring kit.

Since the same fuel pump is used for a LOT of different Kawi's they must be having a lot of people with bad pumps, but it may be that only the "gas guzzlers" have these issues.
It could be one of those combination things where a worn/weak pump combined with a part clogged filter or screen combined with a part blocked tank vent all together combine to reduce the pumps ability to supply enough fuel pressure. When fuel pressure drops below the threshold, most modern ECUs dial down the power to avoid a lean condition.

[maxtog]

Head pressure varies with the height or depth of the liquid.  But what do I know. 

It does, but not by much.  The head pressure might be around 0.33 psi at full tank and 0.11 at one third (when the issue starts)?  But the pump has to produce 44 psi.  Who knows, maybe the pump is ever so borderline in my case that a 0.22 psi loss (0.5%) matters?

Glad you got your bike fixed Max, go out and enjoy it. 

It isn't fixed, it is sitting in a shop for weeks waiting for parts while the weather has been fantastic

But I am hopeful!

[maxtog]

There is now a filter/o-ring kit available    99999-0521

Miracles never cease!

But yikes, $63 on Partzilla for a little screen, 2 screws, and 3 o-rings.  Beats $450 for an OEM "fuel pump [assembly]", if you are wanting just that non-aftermarket part.

[Freddy]

The same pump is used in many Suzuki models.  Most of the parts are available individually.

http://www.dnrmotorcycles.com.au/partFinder/fiche/suzuki/2016/gsx1300ra/fig-172a-fuel-pump#partid-5018401

[maxtog]

They called and said their diagnosis after testing is that the fuel pump would not produce the correct pressure and has to be replaced (no mention of the "filter" pad being the issue).  I authorized it, but the part will take "7 to 10 working days", so now I have to sit and wait weeks

My problem with this, is that even if the pump were defective, as we discussed before, it should not matter the level of fuel in the tank.  And yet that greatly affects when the problem occurs.  So this diagnosis/solution doesn't explain that behavior.   But, I give up- they are the experts.  I guess we shall see.  Eventually....

And I finally got the bike back today (5/14) after work (65,758mi).  $1445 for the diagnostics, fuel pump assembly replacement, and fork seals replaced.

I talked to the lead mechanic.  He was absolutely baffled, just like all of us, as to the behavior of the bike and why the fuel level would matter at all.  But it did- they confirmed it several times.  Anyway, he assured me it is fixed.  The trip home was a short one, but the fuel level was low, and I rolled on the throttle several times (where I could) with no problems.  So hopefully that is the end of this saga.  They gave me the old fuel pump assembly to take home.