81' Mariner 5hp runs for 5-10 seconds and pukes

cosmo6912

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Jul 29, 2003
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Seems to be a fuel issue.....it runs about 5 seconds or so with the choke closed about 3/4 of the way... the idle raises and it pukes unless I feather the throttle alot and then it will go for 5 seconds or so and repeat. Won't run at all with choke open. Carb is clean....had it off and checked it/cleaned it real good. Can it be something to do with that little square block that the fuel line attaches to the side of the carb with? It has the little gasket/bladder thing in it that I am suspect of....looks ok but I am not sure what it does.<br /><br />thanks for the help!!!
 

greasemonkeyozi

Petty Officer 1st Class
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Jul 16, 2003
Messages
282
Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

It can be maybe 3 things. (1) fuel problem. That black square thing is the fuel pump. Its always a good idea to rebuild that thing, wont run over about $4.00. All you need is a diaphram kit.Make sure that the fuel system inside that pump is clean, even on the engine itself. Look for a tar gummy type stuff clogging ports. <br /><br />Another thing is your fuel system might be taking on air somewhere. Check for any fuel leaks from the fuel tank to the carborators. If your fuel lines dont have any hose clamps on the ends of them, add them, and tighten them good. Also, if you do rebuild that fuel pump with a new diaphram kit, take the fuel line off going to the carborators while someone engages the starter to see if the fuel pump is pumping fuel with a good bit of force.<br /> It would also be a good idea to take your carborators apart to look for any sighns of trash in them. take your needle out from under your floats and blow on the fuel inlet where the fuel line goes. If you cannot blow air through there, you got trash in your carb and no fuel is getting to your carbs. It aint no thing to clean them out. While your at it, spray them things out with carborator cleaner and clean those things like you would a pistol, with a fine tooth comb.<br /> (2) Timing. If your motor's timings off, that can be causing it to do that. You can check and set timing on almost any merc with a standard timing gun, but you have to have a shop manual to tell you what the timing is, and what to set.<br /> (3) Electrical. Disconnect one spark plug at a time while someone engages your starter. Hold the plug wires close to the engine and look for a spark.<br /> Before you perform any major maintenance, I advise you to have a good shop manual that covers your motor, a clean and cool working environment, proper tools, patience, and a case of beer. Good Luck ;)
 

greasemonkeyozi

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282
Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

Oh I didnt see that it is a 5hp. It propably dont have a starter, you have to pull start it. If so, do it like I said anyways. Pull that cord and it should be pumping.<br /> Timing shouldnt be such a main concern.
 

cosmo6912

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Jul 29, 2003
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Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

Thanks Chris....I am gonna go get a diaphram kit and hopefully solve the problem. I also am going to replace the fuel line connector that snaps onto the motor, it seems to leak a little when I pump the bulb. Maybe it is sucking air as you say...already got a brand new tank and fuel line....the old tank was shot...the guy I just bought it from left it sitting outside alot.<br /><br />The carb is clean as a whistle....I have cleaned it top to bottom including needle valves and the float bowl, etc...also verified spark to the plug.<br /><br />How does that little fuel pump work? I just don't get how a chunk of metal and a little gasket type bladder pumps fuel.....it must expand and contract since it has a little spring under it....
 

greasemonkeyozi

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Jul 16, 2003
Messages
282
Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

You found your problem. I had an old mer that and gave me the same problem. Believe it or not, but you can buy these parts at wall mart. It will be in the fishing/boating section. Tell you what, go ahead and replace the bulb, that brass connector on the fuel tank where your line connects to, that connector to your motor, and buy some hose clamps.<br /> The way your fuel pump works is it pumps by using vacume from your engine.<br /> Let me know how it goes.
 

cosmo6912

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Jul 29, 2003
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Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

Ok....will try it all....one more question....does the tank need to be pressurized when running or vented? My logic is that it cannot be pressurized or the minor amount of vaccum the motor is using to pull the fuel from the tank will not be strong enough to overcome the gas tank pressure. So in summary....gotta open the little vent on the gas tank or it won't run either....(by the way I have been venting the tank<br /><br />I ask this because it seems like I remember when I was a kid the old motors required the tank to have pressure in it....
 

greasemonkeyozi

Petty Officer 1st Class
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Jul 16, 2003
Messages
282
Re: 81' Mariner 5hp runs for 5-10 seconds and pukes

Well, I keep mine open because the vacume from your engine, or fuel pump pumps fuel. Gotta have a good vent in your tank. Just whatever runs better.
 
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