venting problem on fuel line

[hudman]

I have a 97 rinker viesta vee 266 , replaced the tired 350 merc 2 bbl motor with a 383 mpi motor new from mercrusier. I had a fuel problem that I thought that I had solved by removing the anti siphon valve. afterwards, the boat ran great, until a 1/2 tank then began to starve above 4000 rpm.
I drained the tank today, thinking it was bad gas.
afterwards, i attempted to unhook the vent line from the tank in an attempt to blow it out, in case it had become clogged. when i put air pressure to the vent hose, while unhooked from the tank, it blew back out from the vent fitting on the tank. after some looking up under the deck, and tracing the vent line back to origin, it connects to the fuel filler neck at the back of the boat. This system has no way to vent itself, as the gas cap seals tight!!!! any suggestions? this was the way this was built at the factory, would you reinstall an outside vent, or add a electric fuel pump? the boat runs great when full, but after about 20 gals develops a starvation at above 4000 rpm or upon acceleration
thanks ,, any help would be appreciated...
this is a fuel injected motor, replacing a carb motor
hud

 

[tommays]

Re: venting problem on fuel line

Even if the vent is connected as you say

The tank is still vented to the air and should not build up a vacume as its emptyed unless the screen on the vent is clogged and not allowing air to pass fast enough

i hope you put in a NEW anti spihon valve

Tommays

 

[hudman]

Re: venting problem on fuel line

Even if the vent is connected as you say

The tank is still vented to the air and should not build up a vacume as its emptyed unless the screen on the vent is clogged and not allowing air to pass fast enough

i hope you put in a NEW anti spihon valve

Tommays

WHERE is it vented? it goes to the filler which has a non vented cap?

 

[hudman]

Re: venting problem on fuel line

I have a 97 rinker viesta vee 266 , replaced the tired 350 merc 2 bbl motor with a 383 mpi motor new from mercrusier. I had a fuel problem that I thought that I had solved by removing the anti siphon valve. afterwards, the boat ran great, until a 1/2 tank then began to starve above 4000 rpm.
I drained the tank today, thinking it was bad gas.
afterwards, i attempted to unhook the vent line from the tank in an attempt to blow it out, in case it had become clogged. when i put air pressure to the vent hose, while unhooked from the tank, it blew back out from the vent fitting on the tank. after some looking up under the deck, and tracing the vent line back to origin, it connects to the fuel filler neck at the back of the boat. This system has no way to vent itself, as the gas cap seals tight!!!! any suggestions? this was the way this was built at the factory, would you reinstall an outside vent, or add a electric fuel pump? the boat runs great when full, but after about 20 gals develops a starvation at above 4000 rpm or upon acceleration
thanks ,, any help would be appreciated...
this is a fuel injected motor, replacing a carb motor
hud

 

[gregtay]

Re: venting problem on fuel line

I have a 97 rinker viesta vee 266 , replaced the tired 350 merc 2 bbl motor with a 383 mpi motor new from mercrusier.

Curious... what was involved with converting the boat over to EFI (if anything.) Can you jsut drop in an EFI motor and you are good to go? Figured one day when my carbed 5.0 dies i will want to convert to EFI.

 

[hudman]

Re: venting problem on fuel line

I have a 97 rinker viesta vee 266 , replaced the tired 350 merc 2 bbl motor with a 383 mpi motor new from mercrusier.

Curious... what was involved with converting the boat over to EFI (if anything.) Can you jsut drop in an EFI motor and you are good to go? Figured one day when my carbed 5.0 dies i will want to convert to EFI.

Plug and play, complet motor, with mounts, full exhaust, and everything else. hook up a few hoses, plug in the wiring harness, hook up shift and throttle, and go.,,, just minor problems to iron out

 

[tommays]

Re: venting problem on fuel line

i think its time to TEE in a vacume guage on the inlet side of your fuel pump and see whats really gong on

I gotta think its connected BELOW the cap ? on the filler line which would still allow air with the cap closed


If there was no venting you would never be able to fill the tank and it would have never been CG aproved


Tommays

 

[hudman]

Re: venting problem on fuel line

there are 3 lines coming from the tank, a filler, a supply to the engine, and a vent.
the vent line runs parallel to the filler, up to the cap, looking from the inside of the boat, it fits into the filler neck just below the cap. there is also a ground wire, but no fitting to vent this to the outside of the boat, and no vent inside either. Its the weirdest thing ive ever seen, and ive been around boat building all my life. I know it doesnt take much to vent a tank, a small pinhole will almost do it, but I feel this is the source of my fuel starvation problem.with the tank full, fuel actually spurts out of the line, but once it is down some , not the case.
I am going to TEE the vent line today, and run another line to a new vent , well above the height of the tank, with the tee being low enough in the boat that it doesnt allow fuel to run backwards when filling. any other suggestions?

 

[lilmandavis]

Re: venting problem on fuel line

test run the boat, when the problem develops shut down and unscrew the gas cap and see if you hear suction comming in.

 

[hudman]

Re: venting problem on fuel line

went out and re examaned to make sure i wasnt crazy, its a perko surge plus filler neck assy, with a flashlight i can see the vent, at the top of the neck. the cap looks non vented, it is the type that normally takes a tow pronged tool to remove, it was on very tight. I am reluctant to change things as this was obviously designed to work and has up until now. any other suggestions?

 

[bigbrownbuku]

Re: venting problem on fuel line

its a vented cap. if you have any suspicions the cap has been replaced with a non-vented type THAT type of filler neck REQUIRES a vented cap.

 

[bjcsc]

Re: venting problem on fuel line

I think your problem is in your testing. Instead of pressurizing the vent line, put a vacuum on it. Vented caps are seldom just open to the atmosphere, they usually have a diaphragm that is designed to open when vacuum is applied to the line. I would think this would certainly be the design for marine use as otherwise water would be able to run into your tank as you climbed in an out, took waves, etc. You're testing it opposite to the direction it is designed to flow. Make sure you reinstall your anti-siphon valve - be legal and safe.

PS. I graduated from CBC (now CBU). Hope things are well in Memphis!...

 

[hudman]

Re: venting problem on fuel line

It may be vented, but from a visual inspection, it doesnt look vented. the little chain is still attached to it, looks original to me. I will investigate further

 

[hudman]

Re: venting problem on fuel line

Installed smartcraft gauges saturday, tach and speedo. along with new vhf radio and gps... turns out the cut out at 4000 rpm is by the computer, i am getting a { fault oil pressure sensor} error message, and the computer is not letting the engine rev above 4000. I still have the analog oil pressure gauge hooked up and its showing plenty of pressure, 50 at idle 60 under load, and the motor now has about 15 hours on it, so i know its not the pressure, but the sensor. I will call protec in the morning and go from there.
at least im in the water!!!

 

[hudman]

Re: venting problem on fuel line-not the problem

Re: venting problem on fuel line-not the problem

All is well in Memphis--it seems that the engine problems were caused by a Oil pressure Sensor being unplugged.
the warning beep that went off every 3 minutes has dissappeared, engine pulls strong, and tops out at 4880 rpm, within the 4800-5200 WOT reccomendation. I am turning a 18 1/2 dia 19 pitch 4 blade stainless prop, boat jumps out of the hole like a little ski boat, and runs 39 mph on top end
at 4000 rpm its going 31 mph and getting about 2.75 mpg. at 36 mph the mpg drops to 2, which is still far better then the carb motor ever ran. For those that didnt remember, i know there are thousands of posts here, I have a 97 rinker fiesta vee, a 6500 cruiser, that had a 350 merc 2 bbl, 260 hp motor with a bravo 2 lower unit. Replaced the engine with a 383 mpi bobtail from merc. fuel injected, smartcraft... couldnt be happier. thanks to everyone for their help. Hudman