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  #11  
Old 07-16-2009, 03:13 PM
rudaire rudaire is offline
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Originally Posted by shunra View Post
You are not the only one. I also have a 2002 X-Star and I have the exact same suction sound you described. I have always wondered if it was normal. I don't know where the vent line is though.
peculiar that the only two reported instances of this thus far are on the exact same year and model boat.. I'm going to chase the vent line, which I think I've seen when I pull the center floor panel, this weekend. I ran a tank from full to 3/16 and had no problem with engine performance in spite of the vacuum.. I assume you also haven't had engine troubles caused by this either??

d
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  #12  
Old 07-16-2009, 03:26 PM
rudaire rudaire is offline
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I just spoke to a third 2002 xstar owner who said that 'every now and then he'd hear pressure or vacuum escape from the tank as he unscrewed the gas cap, but it didn't last more than a second'...

May there be a one way check-valve that allows air to enter the tank to replace fuel that leaves the tank, but doesn't allow air (or fuel if the boat sinks) out of the tank?? Maybe the temperature rose during the day and the fuel and air expanded causing the tank to pressurize if a check-valve won't let anything out?..

Can I be sure the vent is literally an open line to the atmosphere on these boats? I also have a scarab, and on that boat the vent most certainly is an open line to atmosphere.
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  #13  
Old 07-16-2009, 06:48 PM
shunra shunra is offline
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Quote:
Originally Posted by rudaire View Post
peculiar that the only two reported instances of this thus far are on the exact same year and model boat.. I'm going to chase the vent line, which I think I've seen when I pull the center floor panel, this weekend. I ran a tank from full to 3/16 and had no problem with engine performance in spite of the vacuum.. I assume you also haven't had engine troubles caused by this either??

d
It happens to my boat everytime I fill it up. I believe is is suction as opposed to pressure build up, but I guess I haven't explicitly checked. It can happen for quite a few seconds if I only undo the cap part way.

I haven't had any engine troubles caused by this. I usually only go from full to 1/2, but have been as low as 3/16 on occation without any problems.
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  #14  
Old 07-21-2009, 12:41 PM
rudaire rudaire is offline
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Quote:
Originally Posted by bigmac View Post
The tank is vented...shouldn't be any negative or positive pressure buildup.
Bigmac,
are you familiar with the setup on the 02 xstar? Attached is a picture of the top of my tank. As we all know, A is the big hose for filling the tank with fuel, C and D are the high pressure line to the fuel rail, and the return line from the fuel rail, and B, the hose that is disconnected from the nearby nipple, is the only 'vent' hose I can find coming from the tank. The only problem is that hose B runs parallel to hose A the entire time, and attaches to a nipple that is clearly visible in the fuel inlet opening on the TANK side of the fuel cap. When I close my fuel cap, block the open nipple you see on the tank, and blow into hose B, the tank pressurizes. If I open the gas cap and blow into hose B, the air escapes there, from the spot where hose B attaches which as I said is on the tank side of the cap. If I repeat the test with the fuel cap on and unplug the nipple on top of the tank, of course the air escapes there rather than the tank pressurizing. Point being, as my system is designed, there is not a vent to allow air to escape unless you leave the gas cap loose, or unless your gas cap o-ring isn't sealing.

I did not repeat this test drawing a suction on the hose as I was afraid I'd somehow end up with a mouthfull of gas fumes, but I do wonder what provisions the system has to allow air INTO the tank to replace burned fuel...I have to believe somewhere there is a way for air to get into the tank.

The only purpose for the vent hose B in my system is to allow for air to escape during refueling, it would burp and gurgle while filling if B wasn't there to route air to the entrance of the fuel filler, air that is being displaced by incoming fuel...

Once the cap is screwed on tight hose B is no longer venting anything..

It is possible that there is a one way check-valve somewhere that allows air into, but not out of, the tank. Possibly even part of the metal round piece that C attaches to that is part of the FPR on the newer models. Haven't tracked down if this is the FPR on my system, but I'm accustomed to FPR's being near the fuel rail..

Last time I refueled I didn't notice any hiss. The time before, when it did hiss, I think the temp had risen 20 degrees or more from the time I refueled to the time i removed the cap, and we had driven the boat only a little bit. I suspect the system had pressurized from expansion of fuel, and i suspect my system is also designed not to let any vapors or air out of the tank.

Seems like all mastercraft systems would share this ventless design, but I only know what is going on with my boat..

If anyone can point me to a vent source or hose that I'm unaware of, or a through hull fitting that vents the fuel system like I have on my early 90's scarab I would really appreciate it..

This seems pretty cut and dried (that my tank isn't vented), but I'm being told otherwise by some very credible members on this forum and as such I need to get to the bottom of whether my system is faulty by not being vented, or whether the info I'm receiving is faulty..

dave
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  #15  
Old 07-21-2009, 01:50 PM
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FancySauceRules FancySauceRules is offline
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I have a 2008 X-2 and have had the issue once. I don't think it is confined to just your boat. My dealer told me it can occur by leaving some excess gasoline around the gas cap, but not limited to that. I just leave my gas cap slightly less than nuts tight, and haven't had the issue since.
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  #16  
Old 07-21-2009, 02:14 PM
rudaire rudaire is offline
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Quote:
Originally Posted by FancySauceRules View Post
I have a 2008 X-2 and have had the issue once. I don't think it is confined to just your boat. My dealer told me it can occur by leaving some excess gasoline around the gas cap, but not limited to that. I just leave my gas cap slightly less than nuts tight, and haven't had the issue since.
I've been doing additional reading on the subject and have seen a post where a 2008 boat, not an x-1 however, had a full tank of fuel vent liquid fuel out a vent line that was on the stern and ruin his decals.. But that boat obviously has a thru-hull fitting on the stern. I'm not near my boat right now, but don't recall a thru-hull fitting for a fuel vent anywhere, and am beginning to believe my boat isn't vented, and that this is how it was designed..

dave
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  #17  
Old 07-21-2009, 02:22 PM
bigmac bigmac is offline
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I don't know if it matters, but I see that your fuel pump uses a return line. Mine doesn't.

Here's my fuel pump...(actually Boofer's, but mine's the same). I have no return line (D)

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  #18  
Old 07-21-2009, 02:28 PM
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JimN JimN is offline
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Quote:
Originally Posted by rudaire View Post
I just spoke to a third 2002 xstar owner who said that 'every now and then he'd hear pressure or vacuum escape from the tank as he unscrewed the gas cap, but it didn't last more than a second'...

May there be a one way check-valve that allows air to enter the tank to replace fuel that leaves the tank, but doesn't allow air (or fuel if the boat sinks) out of the tank?? Maybe the temperature rose during the day and the fuel and air expanded causing the tank to pressurize if a check-valve won't let anything out?..

Can I be sure the vent is literally an open line to the atmosphere on these boats? I also have a scarab, and on that boat the vent most certainly is an open line to atmosphere.
They need to specify whether it's positive or negative pressure. Either can mean the vent line is clogged.
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  #19  
Old 07-21-2009, 03:23 PM
rudaire rudaire is offline
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Quote:
Originally Posted by bigmac View Post
I don't know if it matters, but I see that your fuel pump uses a return line. Mine doesn't.

Here's my fuel pump...(actually Boofer's, but mine's the same). I have no return line (D)

It may matter.. I read where you'd posted in another thread about how your vent hose runs to the fuel inlet (like mine does) rather than to the stern. It seems mine runs to a point in the system that is behind the fuel cap, and that it has no access to atmosphere unless the cap is off or leaking.

Another poster seems to think his boat does the same thing unless he leaves his fuel cap a little loose, which is consistent with what my system would do..

d
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  #20  
Old 07-21-2009, 03:26 PM
rudaire rudaire is offline
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Quote:
Originally Posted by JimN View Post
They need to specify whether it's positive or negative pressure. Either can mean the vent line is clogged.
It would be nice to know that, I agree. But it's pretty hard to determine that from just a sound coming from the fuel cap. It isn't like a gush of air you can feel with your hand. It appears like my system doesn't have a provision to let air out of the tank, like if things heat up and expand.. But I refuse to believe there isn't a provision to let air into the tank to replace spent fuel...

hmmm.
d
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