Gas won't drain from tank! (long)

[stevec5000]

I recently replaced my leaky needle valves with new ones, now the gas won't run out of the tank fast enough to keep the engine running at high speeds. It flowed a lot of gas before with leaky needle valves. It seems that when the needle valves seal well air won't go through them and let gas run down fast enough. Also the 1/4" fuel line is too small to let air bubbles go back up through the fuel, so it stops flowing. I removed the vacuum operated valve and ran fuel line from the petcocks directly to the carbs to get the least restriction but it didn't help.
The vent hole isn't plugged but is a very small pin hole. If I go at 70 down the freeway it starts to miss and sputter like it's out of gas in just a few miles. If I check the fuel line it's empty. I tried driving with the fuel cap open and it helps the problem, fuel doesn't stop flowing but smell of fumes is pretty bad.

I had the same problem on my 750 Seca after rebuilding the carbs. I would drive about 15 miles and seem to run out of gas and have to stop and open the fuel cap for a few minutes and let more run down into the carbs. I replaced the old petcock with a high flow Pingel that has a big hole directly through it when it's open and put on a less restrictive inline filter. That helped a little bit so then I drilled a hole in the top of the tank and put in a fitting for a vent hose, like a dirt bike. I tried running the vent hose down by the steering stem but it didn't help. If I ran out of gas I could blow into the hose and force more fuel out of the tank and into the carbs. I realized that there is a large vacuum behind my fairing so it's not a good place to put a vent hose. I ran a longer hose under the tank and back behind the seat near the battery where there's not a vacuum and it works much better but still didn't solve the problem completely. It doesn't run out completely now but slows down to the point where there is just a trickle of fuel going down the fuel line but it's enough to keep the engine running. You would think that if there is a vent at the top of the tank and a large valve that's open at the bottom the fuel would run out in a large quantity but it don't work that way! It seems that to get the full volume to flow I need either an air pump to pressurize the tank or a fuel pump to suck it out at the bottom.
Does anyone know how to get fuel to flow out of the 1100 tank or am I going to have to drill a hole and put in a vent fitting in it too?

[mitch]

gas

Not trying to be sarcastic, but no one else incl myself has this prob if the hoses are vented right and run properly to the carbs. make sure they dont go belowthe bottom of the cabs to far or they will air lock.I removed the octopus and run my lines direct with no filters off the back nipples on my petcocks it runs great good luck hope this helps Doug M

[Ken Talbot]

If things are working properly, there should not be any air going back up the fuel line at all - it should just be fuel flowing down. You may need to remove your petcocks to make sure the in-tank filters are not all gummed up, and that the fuel passages within the petcock itself are also clear. With just a piece of hose connected to the outlet of a petcock, you should be able to drain the tank in pretty short order, certainkly much fastetr than the running motor will ever use.

Another thing to verify is the float bowl venting. Depending on which carbs you have, this will be a separate set of hoses or it will be passages withih the carb bodies. If the bowls do not vent, the fuel flow will be affected.

[stevec5000]

I know nobody else has this problem, serious replies only please. Yes the petcocks and everything else are fine. I've asked the mechanics at some shops around here and they are stumped too, so I though one of you guys might know the answer.

[Ken Talbot]

Hmm, here's another possibility. When you installed the new needle valves, did you re-check the float height, or more accurately, the fuel level in the float bowls ? If the new needles were just a hair longer than the originals, or if they've got a stiffer spring, perhaps they are now sitting up a bit too high and cutting off the fuel so early that you don't have enough in the bowls for the mains to work properly??

[Snow]

I remember reading either on these forums or on the old list where someone's vent in the gas cap was clogged and acted like how you are describing. I don't know exactly what this vent looks like though - but if the cap is open, that would be completely solved.

Another thing you could doublecheck is your float height. If you old needles/valves were leaking, even if your floats are set to be really low (high if upside down) they could still get gas from the leaking, but with non-leaking valves, the fuel level may run out at times of high consumption.

[stevec5000]

I did have to set the floats a few mm lower than normal to get the new needle valves to close completely. The float bowl does get too low but it's because the fuel line goes dry when the gas won't come out of the tank.

[Ken Talbot]

Please be patient with me, but I'm still having a problem trying to understand where your problem is. You say the petcocks are fine, but you also say the fuel will not come out of the tank.

If you disconnect the fuel lines from the petcocks and run a short piece of hose from the petcocks to a container, how fast does the fuel come out and how long does the flow last?

[Jeff]

As with Ken..... I'm just a bit confused as well. Most of it is with the way you describe the function of the float needle valves.

When fuel enters the float bowl..... the displaced air does NOT exit the float bowl back thru the needle valve. If this were the only place for the air to go.... you would have very poor flow..... and the fuel would chug in spurts as the air bubbles traveled back up the fuel line to the tank. In a properly functioning carb.... the air that is displaced by the incoming fuel exits the float bowl thru the float bowl vents. When the main jet begins to suck fuel from the bowl..... the vents also keep equalizing pressure with the outside air so a vacuum does not form in the bowl. If the bowl vents don't work right..... the pressure differential between the float bowl and the venturi area of the carb throat would decrease and the main jet would not be able to draw as much fuel as it should.

IMHO.... if opening the fuel cap helps.... I would think the problem lies in the tank venting. If the tank is not venting properly.... as more fuel is drawn from the tank and outside air is not allowed to flow in........ a vacuum begins to build up which eventually would be great enough to stop or at least severely decrease the amount of fuel able to flow thru the petcocks. It is just like trying to pour gas out of a gas can without opening the little vent in the top...... it just chugs.... gurgles as air tries to enter back thru the nozzle.... and chugs a little more. You pop open the little vent to allow air in on top of the fuel you are trying to pour.... and viola!..... nice smooth and fast flow.

The best way to check if this is happening is as Ken mentioned..... run a hose from the petcock to a container to catch the fuel and watch the flow for a bit. If the fuel flow does not decrease as the tank is emptied or the flow does not get erratic..... then the tank is venting ok. If the fuel begins to slow down or come in spurts.... then the tank vent is not working as it should. Also..... while watching the flow.... open the fuel cap. If the fuel flow increases substantially.... then the tank vent has too much restriction.

Several other things to check that would impede fuel flow are the tower shaped screen tubes on top of the petcocks that act as at least a basic filter screen for larger debris. They are a pretty fine mesh that can get plugged up with varnish, rust flakes and other debris from inside the tank. The other to check..... is the little dome shaped screens that fit over the end of the float needle seats. They have considerably less surface area than the petcock strainers and are easily plugged up. If these dome screens are even partially blocked.... it can really decrease the flow capacity of the float needle valves.

[Jeff]

Another thing.....

I like to occasionally completely drain my tank by pulling it and removing the petcocks from the tank. If you have any surface rust inside the tank... that last gallon saved for reserve can begin to look pretty crappy since most debris from the pump and from inside the tank tends to settle down to the bottom. If you rarely use the reserve...... or rarely completely drain your tank..... you can get a lot of crud down at the bottom.

As with cars.... the quickest way to plug a fuel injector or filter is to suck up the junk on the bottom of the tank.

[skids]

I once pulled the petcocks from the beast because I thought the screens were clogged. I could never use enough of the reserve to count for anything. I pulled the left one and it was impounding gas! I held it up to the light and sure enough the gas was not leaking through the screen. I blasted it with carb cleaner and it started flowing freely through the screen filter again. It did not appear dirty, there was something that created surface tension... Hell, I don't know!

Another thing, if there is a problem with the vacuum line, it should still work OK with the petcock on prime (bypass the vacuum actuater).

I had a carb once (xs11e) that had a spider web above the fuel valve screen and it also had many rubber bits clogging it.

Check your fuel lines. I have heard of real cruddy ones.

[Ken Talbot]

OTOH, it dawned on me last night that kinked fuel lines can also cause this type of problem. I'm sure there's at least one or two XSives out there who have had this happen. JAT....