Qjet/fuel issue

[captmello]

Ever since I got my boat, it's had a chronic problem with The fuel system. Whenever I let the boat sit, the fuel runs back into the tank. I installed a clear filter, and could see how long it would take to drain back.

Since buying the boat a few years back, I've replaced the fuel pump, fuel line, and had the carb rebuilt. It has always had this problem. However it used to take a couple days the drain back, now it drains in a matter of hours.

The boat runs great. Idles smooth, performs well.

Yes, the well plugs are epoxied.

The other day I thought i read somewhere the the screen/filter in the carb acts as a check valve, is that right?

Thanks for any Ideas.

 

[wakina]

Re: Qjet/fuel issue

The barbed fuel line connecter screwed into the fuel tank outlet on my IO has a check valve built into it. I replace the fuel line to water seperator filter and that is how I discovered it, I removed the fitting to help with getting the old fuel line off. I also have a Qjet but so far have have no problems. Maybe your system has one built in also and it is leaking fuel back to the tank on your boat.

 

[Bt Doctur]

Re: Qjet/fuel issue

The anti-syphon is a safety device to prevent fuel from just flowing out of a broken line.It should be there.

 

[Don S]

Re: Qjet/fuel issue

The only check valves are in the mechanical fuel pump. Nothing in the carb, and the anti siphon valve is not there to prevent gas draining back to the tank.

I would bet you have some debris in the fuel pump. Do you have a water separating fuel filter installed between the tank and the pump?

 

[captmello]

Re: Qjet/fuel issue

The only check valves are in the mechanical fuel pump. Nothing in the carb, and the anti siphon valve is not there to prevent gas draining back to the tank.

I would bet you have some debris in the fuel pump. Do you have a water separating fuel filter installed between the tank and the pump?

I haven't had a water seperating filter on it, but it does have a filter between the fuel pump and tank. Changed every year. Coincidentally, I did buy a new separating filter this winter and plan to install it this spring before splash down.

The fuel pump was new last year.

I'm staring to think I'm going to have to buy/make a fuel pressure tester to test the system.

Unless anyone's has a better suggestion.

 

[wakina]

Re: Qjet/fuel issue

I do not know if the check valve on my boat was factory installed or not, but there is a small round ball that is spring loaded in the barbed fitting that screws into the outlet of my fuel tank that flows into the rubber fuel line to the water seperator filter. It allowed me to phisically blow air thru it from the threaded tank side and out the barbed end that goes to the engine fuel supply hose, but would not let me blow air back in the direction of the tank. It is on a 1990 Stingray SVC 210 and powered with a 5.7 mercruiser Alpha one Gen1.

 

[Bondo]

Re: Qjet/fuel issue

I do not know if the check valve on my boat was factory installed or not, but there is a small round ball that is spring loaded in the barbed fitting that screws into the outlet of my fuel tank that flows into the rubber fuel line to the water seperator filter. It allowed me to phisically blow air thru it from the threaded tank side and out the barbed end that goes to the engine fuel supply hose, but would not let me blow air back in the direction of the tank. It is on a 1990 Stingray SVC 210 and powered with a 5.7 mercruiser Alpha one Gen1.

Ayuh,... That's the anti-siphon valve, so the tank won't drain itself in the event of a fuel line rupture...

 

[captmello]

Re: Qjet/fuel issue

I do not know if the check valve on my boat was factory installed or not, but there is a small round ball that is spring loaded in the barbed fitting that screws into the outlet of my fuel tank that flows into the rubber fuel line to the water seperator filter. It allowed me to phisically blow air thru it from the threaded tank side and out the barbed end that goes to the engine fuel supply hose, but would not let me blow air back in the direction of the tank. It is on a 1990 Stingray SVC 210 and powered with a 5.7 mercruiser Alpha one Gen1.

Thanks for the response, I have an antisiphon valve on mine as well. But I don't think its meant to double as a check valve.

I'm going to have to try Bubba's method before I go buying pressure testers, etc. Just to try to narrow in on the culprit.

I'm pretty sure the float bowl is draining as well, because I would expect the engine to fire and run only to die once the fuel in the float bowl ran out. It seems to be bone dry within a few hours. and won't start without turning over the engine a bunch to get fuel back up. I know the well plugs are sealed.

 

[Bondo]

Re: Qjet/fuel issue

I'm pretty sure the float bowl is draining as well,

Ayuh,... Donno if it'll help the thought process or not Mello,...
But,...
It's pretty much Impossible for the float bowl to siphon back towards the tank....
The gas would have to jump though open air to get back up/ out the needle seat....

My Merc/ Weber/ AFB carb on my 4.3l has been doin' it since I've owned it....
I hotwire the fuelpump while I'm doin' the fluid level checks, 'n the "Sniff Tests" in the motorbox...
She's ready to roar to life by the time I get back to the Captain's seat...

 

[captmello]

Re: Qjet/fuel issue

Ayuh,... Donno if it'll help the thought process or not Mello,...
But,...
It's pretty much Impossible for the float bowl to siphon back towards the tank....
The gas would have to jump though open air to get back up/ out the needle seat....

My Merc/ Weber/ AFB carb on my 4.3l has been doin' it since I've owned it....
I hotwire the fuelpump while I'm doin' the fluid level checks, 'n the "Sniff Tests" in the motorbox...
She's ready to roar to life by the time I get back to the Captain's seat...

Really?? Your fuel is draining back down as well??? Different carb, and different fuel pump. Same issue?

WTH.

I'm going to get to the bottom of this by the end of the summer gosh darn it! I'm on a lifting restriction for another two weeks due to back surgery, so I can't work on the boat yet.

I'm not giving up on this one... again

 

[Fishermark]

Re: Qjet/fuel issue

I agree with the others that it is not draining out back to the tank. It could be your epoxy has failed. Or, it is possible it is simply evaporating due to the heat?

 

[captmello]

Re: Qjet/fuel issue

I agree with the others that it is not draining out back to the tank. It could be your epoxy has failed. Or, it is possible it is simply evaporating due to the heat?

I've been running it with a clear filter between the pump and the carb to test this issue. After sitting for "a while", the level in the filter will have gone down. Once it is empty, I crank over the motor. After a few cranks fuel starts to to come up through the filter. Once the fuel is up through the filter and up to the carb it fires right up.

 

[Bondo]

Re: Qjet/fuel issue

Really?? Your fuel is draining back down as well??? Different carb, and different fuel pump. Same issue?

Nope,... Best I can tell it's droppin' into the intake,... slowly...