72 merc 80 hp will not run but will idle

[dirtbiker338]

i have a 72 merc that won't run but it will idle. I was at the lake over the weekend and it ran just fine for the first day got down to about 1/4 tank and then the motor seemed like it was running out of gas and then died i could get the the motor to start and idle for a few minutes if i tried to give it gas it would die. i tried to drain the float bowls thinking that maby i got water in the gas but still nothing if anyone can help i would be greatful

 

[Wingedwheel]

Re: 72 merc 80 hp will not run but will idle

Try pumping the primer ball while its running to see if you can get past idle. That should tell you if its a fuel issue.

 

[CharlieB]

Re: 72 merc 80 hp will not run but will idle

Verify a nice hot blue spark of at least a half inch.

Just 'bump' the choke as you are opening the throttle, it that improves running it would indicated the idle circuit is slightly crudded up.

Clean the carb(s).

 

[dirtbiker338]

Re: 72 merc 80 hp will not run but will idle

i tried pumping the fuel bulb and it just died think that it flooded out and when i choke it the thing dies too do you think that it could be a filter issue?
i have done everything that i can think of except pull the carbs and do a full cleaning

 

[Wingedwheel]

Re: 72 merc 80 hp will not run but will idle

Sounds like its flooding when you give it any kind of gas past idle. I'd start with a carb cleaning. whens the last time you did, if any, work on the carbs?

 

[dirtbiker338]

Re: 72 merc 80 hp will not run but will idle

I only bought the boat in may so I am not sure when the last time the carbs have been cleaned. But as far as flooding it seems more like it is starving of fuel but first thing I will try is a good carb cleaning

 

[Wingedwheel]

Re: 72 merc 80 hp will not run but will idle

I thought it might be flooding because you said when you pumped the ball it died. if you think its starving, try spraying a fuel mix into the carb while trying to rev it up. Either way if you just bought it, chances are it needs the carbs cleaned or re-built.

 

[CharlieB]

Re: 72 merc 80 hp will not run but will idle

I should have thought of it sooner.

If the fuel pump diaphragm has a pin-hole, or worse, it will leak fuel into that cyl causing flooding, the recirc system will pick-up and distribute some of that excess fuel.

Remove the fuel pump but do not disconnect the fuel lines, pump the primer and watch the vacuum vent for fuel leaking, if so, rebuild the pump.

 

[dirtbiker338]

Re: 72 merc 80 hp will not run but will idle

as i started to take things apart to get to the carbs i noticed one of the lines that comes out the side of the cyl head is broken off it is the one that comes out the middle and goes to the top i dont know if that will do anything or even what it is for but do you think that could be the proublem

 

[Wingedwheel]

Re: 72 merc 80 hp will not run but will idle

What is that line connected to?Carbs? Fuel pump? Can you take a pic?

 

[CharlieB]

Re: 72 merc 80 hp will not run but will idle

The small re-circ hoses are very important to pull excess collected fuel/oil from each cyl and bleed it back into the intake of another cyl. Any clogs in the one-way valves in the fittings or split hoses will upset the balance of the system and cause strange tuning problems.

 

[dirtbiker338]

Re: 72 merc 80 hp will not run but will idle

thank you all for all the input and help the recirulating line seemed to be the proublem but the old merc thanked me for the new plugs and the carb cleaning she ran better then it ever has for me you all rock.