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Blaster21996

05 Wr450f Pressure Build Up In Gas Tank?

17 posts in this topic

I don't know whats going on here! I'm rid'n along and my bike starts stalling everytime I let of the throttle. Then when I stop, it starts pissing all the gas out of the hoses from the carb. I open the gas tank and it decompresses like it had 20lbs of air in it! Then, it runs great till it builds pressure up again, and starts the whole process over again.

Anybody have any clues?

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The tank vent line has a 1-way valve in it that will lock pressure into the tank.

What is the OTHER end of it connected to? Unless they've added a fuel return circuit as a part of the emissions equipment to make it green-stickered, there's no other source where it could become pressurized.

Last resort, pull the check valve and see if it still vents.

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Thanks for responding.........

The other end goes to the steering stem, just like my WR400 and CR500! I took the hose off the tank cap, and it would allow air to pass in either direction (in or out).

The carb has the typical connections that my 2000 WR400 has.

I don't know why it is building pressure faster then the vent hose can release it, but my theory is that..... it is building pressue and is un-able to vent it, so it is forcing it to the carb through the fuel line, and then, being forced out the float bowl overflow line!

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this may sound dumb, but if you take the fuel cap of and shake it does it rattle? if not, could that little ball bearing in the cone be stuck?. i assume this is the 1 way valve.

the other obvious things are to check the hose and blow it out.

I get bush wasp nests in thing like chainsaws exhausts and whipper snipper air in takes. etc

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Interesting that the hose passes both ways.

I wonder if they put the check valve in the cap for the '05 for green compliance... dunno.

It does seem strange that it's happening, and it definitely should not be happening. I'd check with the dealer.

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I will swap gas caps,and vent line with my WR400 the next time I go riding, witch is tomorrow.

The only other variable in this problem is heat. It was around 80 degrees out (the hottest weather I have rid'n this bike in yet), and I was doing technical, tight hill climbs, and the bike overheated a couple of times.

THANKS FOR ALL THE INPUT

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I had a mate who has a 05 WR450 and he had the same deal. It was the valve in the fuel cap. Took it off and put a new one on and it seems to have fixed his problem. Good luck!

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If you checked the hose and can blow through it, it is NOT the hose. It is the check valve in the cap. This isn't rocket science. Sounds like you are on the right track, did the WR400 cap work? If so switch caps or you may try and take some compressed air and pressure up in the reverse direction (with cap in hand, not on tank) to try and dislodge the check valve maybe a little carb cleaner will help loosen things up a bit.

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The check valve only allows fuel and vapor to ENTER the tank. It does not allow pressure to vent. It's an emissions thing.

Heat from the radiators didn't even occur to me as a source of the pressure buildup. If that is the case, then I'll bet that the pressure problem got worse as the tank drained.

Simple solution? Do it the way it was done in 1978... remove the check valve, or replace the cap with one that does not have a valve built in if there's no valve inline.

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I don't know whats going on here! I'm rid'n along and my bike starts stalling everytime I let of the throttle. Then when I stop, it starts pissing all the gas out of the hoses from the carb. I open the gas tank and it decompresses like it had 20lbs of air in it! Then, it runs great till it builds pressure up again, and starts the whole process over again.

Anybody have any clues?

Need to vent. The pressure is literally pushing the floats down by the inlet needle, thus, flooding the carb/engine and draining out the extra via the overflow hose. I'd check the gas gap and line for an obstruction.

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The pressure is literally pushing the floats down by the inlet needle

Ya know... they really should go to a different design that is not pressure-dependent for proper operation.

Downstream valves open when overpressurized.

Upstream valves lock shut.

We try to use downstream valves in Scuba applications.... you can always breathe from a free-flowing regulator and make it safely to the surface... but for drysuit inflation, the valve is of neither design. Instead, the incoming air presses on the side of a hollow pin fitted with three o-rings. This pin has a solid area between the middle and bottom o-rings, and a perforation between the middle and top o-rings.

When the valve is depressed (or the float lowered in our case), the pin slips down so that the air inlet hits the pin on the perforated section, rather than the solid section.

These valves work fine under air pressures ranging from 80psi all the way up to 160psi. The only difference is how quickly the suit (or bowl) will fill when the valve is opened.

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All good ideas! The WR400 cap will not fit the 05 tank. I went riding on Tuesday, and did not have any reoccurring events of the tank pressurizing. I am thinking maybe I accidentally fixed what ever was causing the problem.

Gary

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WheelsUp...... one more thing on this problem, I do believe the heat from the motor and the radiators had a very real effect on this problem. as you pointed out, the problem did not become evident until the gas in the tank was below 1/4 of a tank.

GARY

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Both WR's that I owned did this. I just got rid of the valve and ran a straight hose.

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I am glad to hear that others have had this problem. I am not glad that you had the problem, just that if others are experiencing the same thing, then others have came up with the solution.

If it happens again, I too will dump the check-valve.

GARY

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