TOPIC:

Replaced the fuel line, added an inline filter, and an inline petcock, plugged the vacuum to the tank petcock and leave the tank pc in "prime" position. (its been rebuilt, and leaks..sometimes..or not..or does...so I dont trust it.)

First night out, got 60 miles out on some two lane and it started to die- sputtered to the side of the road, quickly figured out I had the line too short, whole area under tank got hot, rubber hose got warm, folded on itself fuel starve.
Next day re-routed fuel line, made it longer. Ran about 95 miles no problems, ran great.
Few dozen short trips no problems.
Just now was about 35 miles from home, same thing happened, coasted to side of road, waited 3-4 minutes and made it 3/4 of the way home happened again, another 2-3 minutes wait, and off we go.
Looked at the fuel lines-no kinks, high areas, see thru filter is half full of gas. No leaks- but sometimes there is a slight gas smell around the carbs, but they are dry everywhere I can see. Almost more like the smell of gas and an engine that is burning oil, but faint.

thought it might be electrical- you know, after an hour something gets hot and fails, have had things like that happen in the past, but never a start 3-4 minutes later and ran fine.
Sure think its a fuel starve..somehow...but am totally open to suggestions.
thanks

hook a vacuam line back up to stock petcock

Have you checked the tank vent in the cap?
Also disconnect fuel line and check flow into a container.

wireman wrote: hook a vacuam line back up to stock petcock

I leave that one on "prime" its my understanding if its like hondas, yammers etc prime is wide open no?
I'd say that was it except putting on so many miles. I usually kill the petcocks a few blocks from home and sometimes thats all it takes to start puking out

Motor Head wrote: Have you checked the tank vent in the cap?
Also disconnect fuel line and check flow into a container.

LOTS of flow, I'll check the vent in the cap in the AM.

is it possible that somehow the screen in the line into the carb is partially plugged?
thinking outloud, I dont think so, as this usually happens going steady around 3000rpm vs. 4k and up, maybe the vent cap just starting to plug, and yanking the throttle is enough to get it open...

thanks wireman, motorhead, good stuff- any other ideas I'm open

Would test run with fuel tank cap ajar (partially open and not snapped down) to determine whether fuel starvation is resulting from insufficient fuel tank venting.

Good Fortune!

What In-line are you using? One for a Gravity system? those car filters are for like 4-6 psi flowing through them. They can restrict the flow on a bike.

This free-flowing in-line filter usually works well in KZs.

www.z1enterprises.com/Fuel-Filter--High-...ne-clear-14-293.aspx



Good Fortune!

sorta looks like that ^ but paper element.
Good point, if its designed for pressure, even 3 pounds, that 2500-3K lurching along in high gear could be just enough.
I'll check the flow with the lid on and some hand pressure to speed things up.
also, seems to happen more with nearly an empty tank...and that would lend credence to the inline filter, more gas, more weight pressing down..hmmm, Im thinking its the filter..

Yep, low fuel level = less Head Pressure. Change the filter out.

Ah nothing like gearhead think tank.
thanks

I'll do that and post a follow up for anyone searching in the future.

Medina wrote: ...seems to happen more with nearly an empty tank...and that would lend credence to the inline filter, more gas, more weight pressing down..hmmm, Im thinking its the filter..

Imo, points more suspicion to tank vent issue -- not a matter of gasoline volume inside the tank.

Gasoline flows from the tank at the same rate regardless of whether the tank is full or almost empty.

Good Fortune!

Patton wrote:

Medina wrote: ...seems to happen more with nearly an empty tank...and that would lend credence to the inline filter, more gas, more weight pressing down..hmmm, Im thinking its the filter..

Imo, points more suspicion to tank vent issue -- not a matter of gasoline volume inside the tank.

Gasoline flows from the tank at the same rate regardless of whether the tank is full or almost empty.

Good Fortune!

I might be remembering incorrectly, but a full gas tank exerts more pressure on say a 5/16" hole than an empty one as the volume of fuel sitting on top of that hole is greater-more mass pressing down than a nearly empty tank. ...I think...lol, I'm getting used to being wrong however

Patton wrote:

Medina wrote: ...seems to happen more with nearly an empty tank...and that would lend credence to the inline filter, more gas, more weight pressing down..hmmm, Im thinking its the filter..

Imo, points more suspicion to tank vent issue -- not a matter of gasoline volume inside the tank.

Gasoline flows from the tank at the same rate regardless of whether the tank is full or almost empty.

Good Fortune!

Snuck this tibit of info out of an Article on the net.
"A critical variable in this system is the head pressure of the liquid in the product fill tank.
The delivery pressure, or head pressure of the liquid product is greatest when the tank is full.
As the tank is emptied, the head pressure drops."
it does make a difference on fuel Level, as to the flow rate.

Would test run with fuel tank cap ajar (partially open and not snapped down) to determine whether fuel starvation is resulting from insufficient fuel tank venting.

A full tank is less sensitive to vent issues.

Fuel starvation resulting from an obstructed vent worsens as the tank fuel level declines.

Imo, fuel volume flowing through the in-line filter, whether the filter is partially clogged or not, isn't related to the volume of fuel inside the tank.

Good Fortune!

Just think about it for a second, fuel is heavy, each gallon adds to the weight. A full tank weighs more than a low tank. Gravity is applying a force X Weight. More weight more force.

When emptying the bike's full fuel tank through a fuel line from the petcock, it seems to me that the flow volume remains the same from start to finish.

Same with pouring gasoline through the spout from a full gasoline can until the can empties, provided the air vent is open.
Seems the flow volume remains the same from start to finish, regardless of the can's size or shape.

A fuel pump fuel system delivers the same pressure regardless of fuel volume inside the tank, and carbs depend on this steady pressure.

Gravity-fed carbs also rely on the same steady gravity-fed fuel delivery when supplying fuel mixture to the cylinders.

I might be mistaken, but am thinking the float valve doesn't care whether the fuel tank is full or almost empty, and that a float valve won't be less prone to leakage when the fuel tank is almost empty, or more prone to leakage when the fuel tank is full.

Good Fortune!

Recall the kid using his finger to plug a hole in the dike.

He applies the same finger pressure regardless of water level behind the dike.

Good Fortune!

Edit -- pushes harder where the water level is significantly higher, say 50 feet.

It will be more prone to leak when full. Do to the Gravity pulling on the weighted mass in the tank. A tank with 8oz in it would more than likely not leak from float needle and seat. A tank with 4 Gallons in it would be more likely to leak from said float valves. Its pretty basic physics.
In another set up, you could do nothing else but increase the height of the unit of liquid in question, as it goes up the Pressure will increase.

mste.illinois.edu/murphy/WaterTower/default.html

It just seems to me that the mere six inch difference in fuel surface height between full and near empty has virtually insignificant effect on pressure exiting the petcock.

Imo, with reference to fuel starvation, the venting is far more critical than the fuel level.

Where fuel starvation is less pronounced with a full tank, the reason is most likely due to poor venting, and not because more gasoline weighs more than less gasoline or because the level of fuel is slightly higher in a full tank.

Just my 2¢

Good Fortune!

I am by no means an expert on this subject, but I think you are talking about static fluid pressure. Which if I am not mistaken, and I certainly could be, is as follows;

The pressure exerted by a static fluid depends only upon the depth of the fluid, the density of the fluid, and the acceleration of gravity. Static pressure does not depend upon the shape, total mass, or surface area of the fluid.

and is given by the expression;
P(static fluid) = ρgh [where ρ = m/V = fluid density, g = acceleration of gravity, h = depth of fluid]

The most remarkable thing about this expression is what it does not include. The fluid pressure at a given depth does not depend upon the total mass or total volume of the liquid.