It's possible for some form of potentially screen-clogging matter to remain in suspension in the fuel inside the tank.
An example of this is when a fuel tank is painted and excessive over-spray is allowed into the tank interior.
The over-spray becomes small soft globules suspended in the fuel.
With ample fuel in the tank, any suspended globules are further apart and floating in suspension above the petcock's screened intake pipes that are protruding up through the bottom of the tank into the tank interior. When the tank's relatively full of fuel, there's less tendency for the globules to accumulate onto and clog the screened intake pipes.
As the fuel level diminishes, the lesser fuel volume becomes more saturated with the same globules, which increasingly concentrate around and onto the screened intake pipes, and obstructing flow of fuel through the screened intake pipes. Resulting in fuel starvation that's more pronounced with lower fuel levels.
Refilling the fuel tank allows the globules to disburse and float away from the screened intake pipes. Resulting in the return of adequate fuel passage through the screened intake pipes.
Have observed this scenario where a rider in the group had an almost brand new KZ1000 with a beautiful custom paint job, plus a mural painted on top of the fuel tank. Only with a partially filled fuel tank would the bike suffer obvious fuel starvation.
Flushing the tank, and cleaning the petcock's screened intake pipes, completely resolved the problem.
Have not found petcock screens.
Have one missing and one damaged.
Where did you get yours ?
Did you adapt them ?
650ed wrote: I suspect your petcock and mine are different. Mine has 2 screens (one for the "ON" position and one for "Reserve" position inside the tank, plus one in the petcock bowl. All 3 screens inside the tank are pretty fine. I agree that there are decent inline filters that can catch the very fine particles that the petcock screens don't catch, but it seems to me that removing the petcock screens that are inside the fuel tank will allow the larger particles of funky stuff to flow into the petcock and clog it up so it doesn't function as well as it should. When I disassembled my original petcock (manual type) it looked like the tolerances were pretty tight and that it wouldn't take much debris to cause a problem. That stuff shown in you filter picture might have cause a problem for my petcock if it hadn't been caught before leaving the tank. Yours may have a different configuration, because if it had the bowl screen most of that stuff would never have made it to your inline filter. Ed
Tank screen with straight pin head and human hair:
The ebay item id given is invalid, no result has been sentMine are original to the original petcock, and the NOS petcock I bought that is now on the bike came with them too. These folks claim to have them (click on "Non-OEM Parts; Kawasaki Fours; Carburetor; then go about half way down the page) but they sure aren't giving them away.
Tank off, shined a bright light in there, I couldn't see any thing outside a few specs of crap floating around.
however: Pulled shook, shake flipped flushed..put back, still no joy.
Pulled petcock (recall the story of modifying it to 'on' or 'off' bypassing vacuum setup) tore it down, ran a 1/4" drill thru all passages (instead of the metric slightly smaller equal) put back, pressure test to 30 psi, no leaks, it goes back on bike-
Pulled line off petcock, 1/4" dia stream of gas, pull line from in front of filter, stream.
inspect new filter, some tiny specs of something, carb cleaner flows right thru like water..grrr..
Wipe off edge blow gently and air goes right thru (yes, arrow pointing fuel flow has been correct all the time. ) put filter on, trickles..stops..nothing..There is only about a gallon of gas in tank at this time to try and simulate the 100-120 mile fuel starve problem.
Tossed paper filter, put screen filter I had in box that I didn't use when this problem started last year........zing! Flows fine- put 80 miles on with passenger and no problems, will put more on when storm passes.
Lessons for those searching years down the road with same problem
1) ALL paper filters are not created equal
2) All "free flow zero g" free flow paper filters are not "zero g free flow" This one would flow with 4 gallons sitting on top of it, but NOT one gallon!!
3) you look more awesome riding your bike, than sitting on the side of the road pretending to use your cell phone.
petcock screens, inline filter and never remove those inline screens in the intake side of the carb gas rail
I have followed your advise ( April 2012 ) and purchased two petcock in tank filters from reproductiondecals.com.
Ready to install filters. Filter appears to be same dimension as petcock brass tube.
Looking at your pictures : it appears something is around the tube ( a band or sleeve ) connecting filter to tube.
How is this connected ? Both tube and filter same size.
(Perhaps, band or heat or chemistry or some combo. )
Also reserve filter opening is larger than filter therefore loose.
650ed wrote: Mine are original to the original petcock, and the NOS petcock I bought that is now on the bike came with them too. These folks claim to have them (click on "Non-OEM Parts; Kawasaki Fours; Carburetor; then go about half way down the page) but they sure aren't giving them away.
On mine the original screens don't have a separate band or connector. The one screen fits over the extended brass tube and the other screen slips inside the depression in the petcock casting. If the screens they sold you don't do this you may want to call them and ask how they are intended to fit. If there's a problem with the fit they must have run into it before because they've been selling the screens for a pretty long time. Hopefully they have a satisfactory solution. Ed
Spoke with reproductiondecal.com, their experience is that the filter should slide over tube.
Upon examination : The petcock tube is flared at the end.
Choice of cutting off 1/16th or so; or a add a sleeve.
Not certain of problems in shortening brass tube, went for a less permanent solution first.
Using a sleeve cut from the cap of a Bic pen : snugfit for filter and onto tube.
If gas does not dissolve the plastic it is a good fix.
Left old filter on the reserve location.
( There is a Long story of original gastank and work done on bike by others. )
Interesting. I measured the OD of the screen on mine and it is about .0372”. If yours is the same it should in theory fit correctly into the reserve hole in the petcock (see pics below). I measured the OD of my C1’s petcock’s brass tube and it is about .314”. Ed
Arthur A wrote: ...Using a sleeve cut from the cap of a Bic pen : snugfit for filter and onto tube. If gas does not dissolve the plastic it is a good fix.....
To help determine whether it's fuel-proof, could immerse a piece of the plastic pen cap in gasoline for a few days, and see if it softens or dissolves.
As an aside, a plastic milk carton should not be used to store gasoline, because the gasoline will melt through the carton, perhaps after a few days.
Pity the poor soul who sets the milk carton filled with gasoline on a storage shelf inside the garage.
Current gasoline has caused leaks in the stock fiber glass fuel tanks on vintage motorcycles.
The brass tube is 1 11/16" long (see pic). Because the length of the tube is what determines the amount of fuel left in the tank when you must switch to reserve, shortening the tube will reduce the distance you can travel on reserve. Can you use emery cloth to correct the damage? Ed