How to siphon gas from 1991 OMC Cobra 4.3 ho?

[Shaun E]

First of all I am a complete newb to engine repair and boat ownership in general. I purchased my boat from a man who had it sitting in storage for the last 2 or 3 years. The engine is a 1991 OMC Cobra 4.3 Litre HO.

I had it serviced, an oil change, and the mechanic told me to siphon the gas out of it or it will "gum up" the carburetor.

1.) This makes sense but is it completely necessary or can I just add some fuel system cleaner?

I tried to use a pump to siphon it out of the gas tank through the area you add gas, but this didn't work and from reading through this forum for the last few hours I realized that the boat has an anti-siphon valve.

2.) The forum said to go through the engine side of the primer bulb or other areas such as the fuel line. I have no idea what the primer bulb looks like. Is there anyway someone can send me a picture of the primer bulb or of the location where I can siphon the gas. (Like I said complete newb)

3.) Also, if the tank is full, how much gas should I expect to come out of the tank?

Thanks for any help provided!!

Shaun

 

[jerryjerry05]

Re: How to siphon gas from 1991 OMC Cobra 4.3 ho?

If your tank is full???
I'd bet it's OK.
Now if it was at 1/2 that leaves room for condensation.
Most OMC's have a water/fuel seperating filter.
Make sure it's new and tilt the boat up in the front as far as it can go.
This makes the water flow back to the pickup tube.
Then start it and run it for a while.
Shut it off and check the filter for water.
A lot? Or a little?
If there is water? Depending on how much?
You can remove the anti siphon valve and install a hose fitting then siphon off the water.
Just a little the filter will catch most of it.
Or adding dry gas or stove alcohol will get rid of the rest.
The squeezie is an outboard primer bulb.Installed inline it helps siphon off the gas.

 

[heyyou325]

Re: How to siphon gas from 1991 OMC Cobra 4.3 ho?

A better question than is the tank full, is did the previous owner put stabilizer in the gas. I've got some less than a year with stablilizer in that I have to take out today. What sort of a fuel pump do you have. If not electric, you can buy one (12 volt in line) and put temporarily in the line most anywhere you can attach it. Pump the fuel out and into containers. I'm going to filter mine a couple times to try to clean it. I have flakes probably coming off the side of the tank, and a little coagulation (not sure if it's still called varnish) in the fuel. Fuel will start to go bad in a couple of weeks without a good stabilizer in it, especially with the alcohol in it. Alcohol used to be used to enhance it in the 60's and 70's, but this new stuff doesn't. Even way back when, it would varnish and set up hard on you. Plugs filters, pumps, and jets in carbs. An electric pump will pump full time when it has juice to it, so isn't a good idea to leave in line, but it works good to get most of the fuel out. There will be a little left in the bottom of the tank. Leave the gas sit a day or so, and water will separate out. And I believe sink to the bottom (might be top, my memory isn't always right), you can see it in a clear jug. Altho the alcohol holds the water, some will still separate. Jerry is right also, just depending on what is wrong with the gas.

 

[Lou C]

Re: How to siphon gas from 1991 OMC Cobra 4.3 ho?

Whatever method you use, be careful because gas vapor is explosive. During the hurricane Sandy aftermath, I used a hand pump to pump out gas through the the gas sending unit opening of the fuel tank. You remove the access panel to the tank. Then you lift out the sending unit and snake down the siphon hose into the tank. If you use an electric pump make sure it's rated for gas and that you make the wiring connections far from any gas vapors.

 

[HT32BSX115]

Re: How to siphon gas from 1991 OMC Cobra 4.3 ho?

Howdy Shaun,


Welcome aboard!

I had it serviced, an oil change, and the mechanic told me to siphon the gas out of it or it will "gum up" the carburetor.

Old gas will not only lose octane, which can result in detonation, it will also lose vapor pressure making the engine harder to start.

1.) This makes sense but is it completely necessary or can I just add some fuel system cleaner?

You cannot "clean" old gasoline. You can only remove it and/or dilute it.

I tried to use a pump to siphon it out of the gas tank through the area you add gas, but this didn't work and from reading through this forum for the last few hours I realized that the boat has an anti-siphon valve.

The anti-siphon valve has NOTHING to do with siphoning it out of the fill port.

It's almost impossible to siphon out of most fill ports/tubes....because the actual siphon-hose must make more than a few "bends" to even get into the tank. It's best to do like LouC suggested............ remove the gage sender and use a suitable hose to siphon out of the approx 2"-3" hole. I use a fairly long piece of 3/4" clear vinyl hose with a valve and piece of 1/2" pipe on the end you'll use to place in the container you siphon into. (Fill the hose before you try to start the siphon)

2.) The forum said to go through the engine side of the primer bulb or other areas such as the fuel line. I have no idea what the primer bulb looks like. Is there anyway someone can send me a picture of the primer bulb or of the location where I can siphon the gas. (Like I said complete newb)

Primer bulbs are associated with outboards. You have an I/O

3.) Also, if the tank is full, how much gas should I expect to come out of the tank?

Depends on how many gallons the tank holds! (REALLY!) You can get just about all of it.

I don't hesitate to use 2 year old gasoline ............. But I will only use it after diluting it with fresh gasoline. 50:50 or more (60:40 etc.....)

I wouldn't run it straight in a boat. (I would run 2 year old gas in a car though, after filtering it and maybe diluting it with fresh gas too....)


Regards,


Rick