fuel problem

lathehand

lathehand

Junior Member
I'm helping a friend with his 1986 90hp merc inline 6 .It starves out of fuel every so often.When it dose that the primer ball colapses and stalls out .At first I thought it was a clogged vent We've put it on a seperate gas tank and no change. Then we changed fuel lines and primer ball and redone the carbs.Still ng.Haven't touched the fule pump except to check the straner it was clean.I'm thinking if the diaphrams were bad it probably wouldn't run as good as it dose .sometimes it runs for a hour and it's fine sometimes it acts up after only a few minuets
 
Lathehand, I don't know the answer, but simple physics says that the ONLY way that the primer ball collapses is if it is under a vacuum That means that the engines' fuel pump is working properly and you can probably eliminate everything engine wise from where the fuel line connects to the engine up to the carbs. Sounds to me that somewhere a vent is not open or there is a clog. When you switched fuel tanks, did you make sure that the new tanks vent was open? Does he have a fuel filter and if so where is it located...before or after the primer bulb? :head:
 
Destoyer thats why I didn't replace the fuel pump diaphram.The air vent was deffently open on the other tank .Now just a thought do you suppose the extra tank I used had a 5/16 hose and the boat has 3/8 hose could be starving it in a diffrent way.I rember you saying you have a mid 80s merc 90 .Has it ever happened to you
 
if i am reading the timeline right, you ran it on the portable tank, same problem, then changed lines, bulb, etc. if so, try it on the portable with new lines.

didn't those have a funky bayonet style fuel quick disconnect, try bypassing that

just throwing out ideas
 
lathehand said:
Destoyer thats why I didn't replace the fuel pump diaphram.The air vent was deffently open on the other tank .Now just a thought do you suppose the extra tank I used had a 5/16 hose and the boat has 3/8 hose could be starving it in a diffrent way.I rember you saying you have a mid 80s merc 90 .Has it ever happened to you
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HADa 1984 90 hp merc. Sorry I ever got rid of it. I still have a 115hp inline6 that needs a boat under it.

No, this problem has never happened to me.
 
phatdaddy said:
if i am reading the timeline right, you ran it on the portable tank, same problem, then changed lines, bulb, etc. if so, try it on the portable with new lines.

didn't those have a funky bayonet style fuel quick disconnect, try bypassing that

just throwing out ideas
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Yes, they use the old style Mercury quick disconnect. And you're right, there might be a piece of junk caught in the quick disconnect at the tank. Can't be at the engine, since the primer bulb wouldn't collapse then.


Lathehand, quick question.... What kind of tanks are you using? Are they both portable plastic ones? I ran across a problem in one of my older 6 gal portable tanks the other day... seems the internal pick up hose was made out of some kind of rubber, and the Ethanol fuel made it crumbly and brittle. If you had the same problem, and a piece got logged in the quick disconnect on the hose side, then even if you switched tanks, presuming you put the old disconnect on the new hose, that might account for your problem.
 
Sounds to me like one of your fuel hoses is collapsing (somewhere before the bulb). This has been a big problem with the ethanol gas. The old fuel lines cant't handle the new gas and tend to break down inside the hoses. Had the same problem, different engine, and changing to new hoses solved the problem. If you didn't say you ran it off a seperate tank, I would have told you that something in the tank is blocking the pickup.
 
It's on a pontoon boat and it has aluminum tank and the portable is a atwood plastic one only about two years old.The line I was the same one as on the onboard tank becuase the fitting was diffrent the motor has the old style.
 
You need to try to run a new hose from the plastic tank straight to the bulb. Just run a cut end of the hose directly into the plastic tank into the gas. If the bulb still collapses, it has to be the checkvalve on the intake of the bulb. I would bet money that the fuel hose has delaminated inside the hose. Fuel hoses are a hose within a hose. The inner one collapses after continued use of ethanol gas.
 
I only buy ethanal approved fuel hose.The hose that I'm using at this time is about 2 weeks old.And i alwys use stabill in the gas
 
Finally found the problem thank for all your replies.heres what i found .As I said earlyer it's a friends pontoon boat I'm not the only one who has ever worked on it .Anyway someone had installed a fuel water seperator and used a 1/4 in hose barb on the end going into the seperator from the tank how it didn't leak is beyond me and a 3/8 barb going to the motor The 1/4 in barb had a peice of crap clogging half the hole.So between the hole being so small to begin with and half clogged it's a wonder it ran at all.Anyway but 5 trouble free hours it .And life is good again Thanks again everyone
 
lathehand said:
Finally found the problem thank for all your replies.heres what i found .As I said earlyer it's a friends pontoon boat I'm not the only one who has ever worked on it .Anyway someone had installed a fuel water seperator and used a 1/4 in hose barb on the end going into the seperator from the tank how it didn't leak is beyond me and a 3/8 barb going to the motor The 1/4 in barb had a peice of crap clogging half the hole.So between the hole being so small to begin with and half clogged it's a wonder it ran at all.Anyway but 5 trouble free hours it .And life is good again Thanks again everyone
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Fantastic on finding the problem. :clap:

It's why I asked
Destroyer said:
Does he have a fuel filter and if so where is it located...before or after the primer bulb?
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Although I was thinking of just a clogged filter, not a reduced hose barb also. In all cases, congrats again...:beer:
 
Good job, sounded like something plugged up to me too. Some people have all the luck half *** piecing things together, if it were me I would have blown up off shore.
 
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