KLR 650 will not keep fuel line full

Why wouldn't the fuel line stay full between the fuel tank and the carb?

I can fill the fuel line by letting the petcock drain into it (fuel line off petcock). As it idles it empties down to nearly the same height as the top of the fuel bowl with the fuel line attached.

I could understand this easily if I was filling the fuel line and allowing it to drain down as the engine consumed fuel.

I can't understand why with a drop the fuel line will not stay full. Shouldn't the fuel line fill from the tank as it is used?

I have disconnected the fuel line and drained fuel from the petcock through a clear line into a drain pan and there is a steady stream of fuel.

I have disassembled the fuel cap to check for debris or damage to the tank vent.

I have started and idled the bike with the fuel cap open and got the same results.

This bugs the shit out of me. The only thing I can think of is that there is enough air in the fuel valve (petcock) that the pocket of air moves into the fuel line as the fuel moves towards the carb. Still, I would think that siphon alone would cause the fuel line to stay full and or the air bubbles would rise into the tank as it's the highest point.

Any ideas?

By chance...

Does this happen when you add fuel to the tank?

I dunno if this was rip on me or not. If so, good one.

The tank is half full right now. It occurs with the valve in both the on an reserve settings so fuel level shouldn't be part of the cause. I also disabled the automatic shutoff by removing the o-ring in the valve to see if it made a difference and there was no change.

Does it still run OK?

Pumping fuel into a tank forces air in. I thought you might be getting an airblock that way...dunno..

Every so often it would seem like it would hesitate just a smidge when it was on the needle at about 60 mph holding the throttle steady. I was beginning to think that it was starving for fuel.

It wouldn't consistently feel "off" and I realized it was float bowl venting. I did the "t" mod on the bowl vent earlier and had problems with it. I think I have corrected that problem by adding diffusers to the end of the vent lines and making sure they are well hidden from direct airflow.

I ran it this morning with two "Radio Shack" shims under the needle and it didn't feel like anything was amiss. I didn't really gain anything but I didn't notice the hesitation. It does run out of power at about 90 mph but pulls well up to 80+ and gradually looses acceleration. I don't ride over 70-75 so that's not a real issue. Besides, a KLR isn't supposed to be a Bonneville record setter. I never expected it to be so.

Right on, I was hedging my bets.

I'm sure that there is a hydraulic/pnudraulic (misspelled) principle that applies here. I'm probably just getting paranoid and need to not worry about it.

Next winter I want to go to fuel injection http://www.microsquirt.info/ and put this CVK40 up on a shelf and forget about it.

This belongs in Thumpers
And so it goes

JJ

Are the screens inside the tank clean? Drain the tank, pull the petcock and make sure your screens aren't clogged.

There's two hoses that connect to the petcock. One (the larger) is the fuel supply to the carb. The other (smaller) is a vacuum line that opens a vavle in the petcock to let the fuel flow when the motors running.

1. See if the smaller hose is connected tightly at both ends.
2. If connected at both ends tightly, there might be a small leak in it.
3. If the above doesn't work...BURN IT

And so it did.

Thanks for the suggestion.

The tank was recently disassembled and interally coated with POR-15 because it was rusting ( another long and sordid tale). In addition I disassembled, inspected the petcock and reassembled it after removing the o ring on the automatic fuel shutoff to disable it. However, I will have to look at it again if the problem is not resolved through other measures.

I will replace the vacuum hose in order to be sure it's not leaking.

I did spray starting fluid around the carb to see if it would change the idle and indicate a vacuum leak and noticed no change.

If I had everything to do over I would have sold this bike a week after I bought it. One of these days I'll learn to pick my battles with more care.

I'll buy it. No problem is all that complicated on a KLR. Have you checked the vent tube running under the seat from the back of the tank? Kinked during install? Clogged it when they sealed the inside of the tank?

I use clear fuel line on my bikes, lawn mower, snow blower, etc. I have never seen a clear fuel line run full on a gravity feed system. There is always some "air" or fuel vapor present. If it really bothers you, put on a rubber line and you won't see it.

that was gonna be MY suggestion too

+1 on that.

The fact that you see air (fuel vapor?) in the fuel line is no sign the engine doesn't get enough fuel. You see that on every gravity fed motorcycle.

There must be something else going on. Either the vacuum petcock doesn't work like it should, the fuel filter is clogged, or the tank pulls a vacuum (jammed breather?).

Point well made.

You wouldn't want to buy this thing for what I would have to sell it for! No, there isn't anything complicated about a KLR but there are several things that are expensive about it.:huh

The vent tube is free and clear.

I just re- read your post and realized you didn't say anything about it not running, just that there is air in the line. I run a clear line on mine, and there is always air in the line, about level with the fuel bowl..... What is the problem? Just that it bugs you? If it runs, ride it, quit worrying about it. Any bike with gravity feed will do that. Jeebus. Are you just fishing for a reason to get a new bike? If so, bravo!