gas tank pressure

[rossthaboss11]

ok so i was riding my ski today it was going pretty well. then it dies on me. and after that it would always start up right away with a quick pump of the primer but if i gased it, it would fall on its face and die. i couldnt get it to go more then half throtle. my one way check valve is working but i noticed when i pull that there isnt any pressure in the tank. no air shoots out like it should. where else can i be losing pressure, if this is the problem. when i blow air into the valve it holds it. but when i ride then pull it theres no pressure

 

[SharkB8]

Twice now I have forgotten to reconnect my tank vent hose, meaning that there was no tank pressure whatsoever, and I couldn't even tell. I doubt that's your problem.

I'm no expert, but I would start with the fundamentals - make sure the fuel lines are clear, try Reserve instead of On, pull the carb and blow some air through it to make sure its clear.

 

[rossthaboss11]

yea i was going to try all that. theres always air in my gas lines and im not sure how to get it out. not sure if thats a problem either.

 

[SharkB8]

I always have a little air in the line going to the carb and a lot of air in the return line. So far it hasn't caused any problems.

 

[brett]

check the one way tank breather valve...you can get a cheap one at any auto store if it doesnt work

 

[rossthaboss11]

ok that definitly helps cause i wasnt sure if that air in my gas line was causing the problem. the one way valve works just fine i checked it a million times by now. let me ask this question tho, are your plugs wet when u pull them after idling or just running it in the driveway? ive gotten different responses on this. my tuning isnt right. according to group k and how they tune the low speed on the trailer it wants to be way leaner. but when i ride it rides better richer.

 

[Mile9c1]

Your fuel tank doesn't have to be pressurized. I'm not sure where you got that idea from... your fuel pump SUCKS fuel from the tank into the carb.

Maybe you have a bad fuel pump. Or some water in your carb.

 

[SharkB8]

He mentioned Group K - he was probably reading their web site - it says that the tank should be pressurized. Maybe for highly modified engines it has to be??

Earlier this year my ski would only run about half throttle and it ended up being a bad plug wire. You might wanna check for spark on both plugs. May not be your problem but its a 5 minute test.

So the ski will run and idle in the driveway? In the original post it sounded as though it would run only when you keep priming it.

BTW, what kind of motor is it?

 

[Shadow7874]

So, what pressurizes the tank in that case?

I know i had a problem with the line that runs to the one way vent getting kinked where it vented up my pole on my 550. I think that caused some problems, but there shouldnt be pressure in your tank as far as i know.

 

[cleetus]

the tank should have some pressure, it helps the carb suck fuel. I would replace your fuel filter, and then remove your return line from the carb and see if you can pressurize your system... If you cant then I would try to find the leak, just try different sections and use a plastic clamp to pinch the lines and pressure test you should be able to narrow down the spot that it is leaking....

 

[rossthaboss11]

ok ill try that out. its a 701 61x with a 46mm mikuni. it always runs and revs up and down fine in the driveway no matter what. then on the water something happens where if i give it throttle it falls flat on its face just about and dies. with one shot of the primer it fires right back up. if im riding slow and give it primer then pull the throttle it will rip hard for a couple seconds then die

 

[McDog]

Make sure the check valve is letting air IN. It's easy to put it on backwards and not realize it.

 

[aramis]

I'd replace the fuel filter, clean the internal filter in the carb and make sure that the pulse (pump) side is in good shape (clear diaphragms are good, etc).

Also, you might want to take the on/off/res switch out of the loop. Bypass that and see if the problem still happens.

 

[stanton]

sounds like you got some clogged fuel lines.

 

[rossthaboss11]

not sure what happens but something keeps getting clogged. the internal fuel filter didnt really have ne thing in it. maybe a little bit of crap but hardly. wheneven i take the carb all apart and blow through all the fuel lines ect. it runs fine again after. but the problem has come back a number of times. today it ran good, but i cant tune it right for some reason.

 

[FX-Rex]

Are you using an OEM fuel filter?

 

[stanton]

not sure what happens but something keeps getting clogged. the internal fuel filter didnt really have ne thing in it. maybe a little bit of crap but hardly. wheneven i take the carb all apart and blow through all the fuel lines ect. it runs fine again after. but the problem has come back a number of times. today it ran good, but i cant tune it right for some reason.

hmm im thinkin you got something in your tank or fuel filter. put on a new fuel filter and drain the tank out into a gas can using the fuel lines as a siphon.
that will clean the gas out that you have and then check the tank for debris.
i had the same problem last weekend and just pulled the fuel pickup out of the tank after the ski died. blew the gas out backwards through all the lines onto the ground, put it all back together and its been perfect since.

 

[BruceSki]

did you check the fuel selector? maybe it is bad/and or clogged.

 

[Mile9c1]

He mentioned Group K - he was probably reading their web site - it says that the tank should be pressurized. Maybe for highly modified engines it has to be??

No, there's nothing that pressurizes the tank, except vapor pressure from the fuel. Which is always changing, so it could never be a "part" of the fuel delivery equation.

The vent let's air in when the level drops, to prevent a vacuum.

 

[SharkB8]

FWIW, here is what Group K says:

All pwc utilize a sealed fuel system that has a check valve on the gas tank vent. This check valve (which permits pressure in the gas tank but not out) causes pressure in the gas tank that helps deliver fuel to the carb(s). Any air leak in the fuel system that permits the leaking off of this pressure, will also affect fuel delivery to the carb(s) at low speeds. To test for leaks, follow this procedure. [...]

That was taken from: http://groupk.com/tec-carbs97.htm

The topic is also discussed again in the last section on that page. Too long to post here.



Now having said that, I have noticed that my relatively mild machine is not affected by lack of pressure in the fuel tank. They build race engines so I don't think they're talking about near-stock machines like mine.