Older Mercruiser 188 fuel system question

[xeddog]

My son has acquired a 1976 Silverline 22VHT with the Mercruiser 188 drive. He has a problem in that whenever he lets the boat sit for more than a day or two, all of the fuel will drain back into the tank including all of the fuel in the carb and all but a little bit of fuel in the bottom of the separator. So the next time he wants to start it is quite a chore. He brought it over yesterday to see if we could fix it.

I'm not sure what the regs were back in 1976, but is "seems" to me like it might be stock. In the attached picture, the part that I cannot name looks like an old-time glass fuel filter, but there is a placard inside that says if there is fuel in it to replace the fuel pump. I am hoping that this is an early version of the fuel line that nowadays runs from the carb back to the fuel pump and is therefore CG approved. Correct???

Anyway, the other thing is that there does not appear to be any sort of check valve in the system. We want to add one but don't really know where the best place to put it would be. I think we will just try to add one in where the fuel line comes out of the tank. I have read that many boats have one located there.

And lastly, any other suggestions to fix this are welcome.

Thanks,

Wayne

 

[mkast]

Re: Older Mercruiser 188 fuel system question

The glass bowl is used to indicate a ruptured diaphragm in the fuel pump.
The fuel line, present day, runs from the fuel pump to the carburetor.
If the diaphragm ruptures, the fuel will dump into the carburetor.
On most check valve installations, the check valve is located at the fuel tank fuel outlet.

 

[haulnazz15]

Re: Older Mercruiser 188 fuel system question

Yes, the sight glass is just the previous failsafe for a ruptured fuel pump diaphram. It works just fine, but you can add a fuel nipple and some clear fuel line to the carburetor if you feel it's necessary. I don't know why you'd want to get rid of the sight glass though, personally.

We have fuel line shut off valve on the line from the tank to the fuel pump.

 

[xeddog]

Re: Older Mercruiser 188 fuel system question

Thanks guys, I was hoping that was the case. But I thought about running a line to the carb, but there is no place on the carb to attach such a line so we will just leave it as is.

As for the fuel shut-off - hmmm. Good idea.

Wayne

 

[mkast]

Re: Older Mercruiser 188 fuel system question

From United States Coast Guard (USCG) Regulations:

Each fuel line from the fuel tank to the fuel inlet connection on the carburetor must:

(a) Be above the level of the tank top; or

(b) Have an anti-siphon device or an electrically operated fuel stop valve:

(1) At the tank withdrawal fitting; or

(2) Installed so the line from the fuel tank is above the top of the tank; or

(c) Provided that the fuel tank top is below the level of the carburetor inlet, be metallic fuel lines meeting the construction requirements of ?183.538 or ?USCG Type A1? hose, with one or two manual shutoff valves installed as follows:

(1) Directly at the fuel tank connection arranged to be readily accessible for operation from outside of the compartment, and

(2) If the length of fuel line from the tank outlet to the engine inlet is greater than 12 feet, a manual shutoff valve shall be installed at the fuel inlet connection to the engine.

 

[Bondo]

Re: Older Mercruiser 188 fuel system question

He has a problem in that whenever he lets the boat sit for more than a day or two, all of the fuel will drain back into the tank including all of the fuel in the carb and all but a little bit of fuel in the bottom of the separator.

Ayuh,.... That's pretty much Impossible....
I'd sooner think the gas is leaking outa the carb, into the intake...

It's physically Impossible for gas to siphon Up through the needle valve...

 

[xeddog]

Re: Older Mercruiser 188 fuel system question

It's physically Impossible for gas to siphon Up through the needle valve...

Perhaps if the needle valve is truly close tight and I will have to admit that the carb is a little suspect too. Also, mkast's information (thank you very much for that), has me wondering about the location of the tank vs the carb inlet. The engine does sit pretty low down in that boat, but after working on the boat for a whole day I can't remember if the tank is lower than the carb or not. If the carb is lower than the tank, that seems like it would "add fuel" to your argument that is is going down the intake. I'll have to check that out again.

But I have a couple of problems with that theory. First, I would think if the fuel is leaking through the carb into the intake there would be a strong smell of gasoline and there isn't. The engine compartment smells completely normal (if there is such a thing). Removing the spark arrestor doesn't produce a very strong gasoline smell either. Not an unusually strong smell anyway.

Second, we are talking about a quite a bit of gasoline. That fuel filter/separator is pretty big so I would say somewhere around a pint of gas each time he lets it set, so where is it going? If it was going into the intake it seems like the majority of it would wind up in the engine oil down in the crankcase and that doesn't appear to be the case either.

Third, if it was pulling the gas into the intake, wouldn't it just keep siphoning until all the gas was gone or the intake filled up?

And I just thought about this. Maybe there is something wrong with the carb so it very slowly leaks fuel from the bowl into the intake. The leak is slow enough that it takes a couple of days for the float level to drop. Then the needle valve un-seats and the rest of the fuel is siphoned back into the tank. How does that sound?

Wayne

 

[Aloysius]

Re: Older Mercruiser 188 fuel system question

It IS impossible to siphon fuel out of a carburetor through the fuel line...it fills ABOVE the fuel level. Fuel will NOT siphon uphill and dump in the carb/intake.

There's only a couple ounces of gas in the carb..doesn't take much to drain the carb.

all old Holleys leak fuel.

Certainly the system from the fuel pump back can drain into a fuel tank.

 

[zbnutcase]

Re: Older Mercruiser 188 fuel system question

An 888 should have a Rochester 2GC on it, not a Holley. And it could be possible that it has pinhole/porous casting leaking fuel into manifold, found a Q-Jet with that very problem once.

 

[dubs283]

Re: Older Mercruiser 188 fuel system question

An 888 should have a Rochester 2GC on it, not a Holley

888 is a ford 302 which came equipped with a 2 bbl Holley carb

the 898, which is a chevy 305 had a 2bbl rochester

 

[haulnazz15]

Re: Older Mercruiser 188 fuel system question

888 is a ford 302 which came equipped with a 2 bbl Holley carb

the 898, which is a chevy 305 had a 2bbl rochester

Yeah, he hasn't specified which version he has, but I'm guessing the Ford 302/188HP. Either way, the fuel draining back into the tank isn't likely the issue.

 

[xeddog]

Re: Older Mercruiser 188 fuel system question

Not sure which carb it has, but I will check into that. As for the engine itself, I'm guessing it is the Ford since the distributor in is front. We were told that it was probably a 351 so how can I tell the diff between the 302 and the 351?

Wayne

I just IM'd my son and it is a Rochester 2bbl carb. He is at work so can't be more specific.

 

[mkast]

Re: Older Mercruiser 188 fuel system question

If it's a 351, the firing order will be "cast" (raised numbers) in the intake manifold.
If it's a 302, the "cast" firing order will be ground off and the 351 firing order will be "stamped" in the 302 intake manifold.

 

[zbnutcase]

Re: Older Mercruiser 188 fuel system question

888 is a ford 302 which came equipped with a 2 bbl Holley carb

the 898, which is a chevy 305 had a 2bbl rochester

It could come with either according to the parts book, but the vast majority i have seen in 23+yrs in the biz have the 2GC...

 

[xeddog]

Re: Older Mercruiser 188 fuel system question

Just in case you missed the edit I made to my previous post, the carb is a 2bbl Rochester. My son is at work and so we cannot get any more specifics.

Wayne

 

[xeddog]

Re: Older Mercruiser 188 fuel system question

Well! I have made a major faux paux. Turns out that he does not have the Mercruiser 188 but the Mercruiser 233. Now that HAS to be the 351. Right? It still has a 2bbl Rochester though.

Wayne

 

[haulnazz15]

Re: Older Mercruiser 188 fuel system question

If it is a 233, then yes, it is a 351. The Carb would still be the same.