mercury 25hp outboard, later 1970's

[shutterbugdm]

really stumped here, I have replaced fuel tank, external fuel lines including bulb, male connector for fuel line and new/rebuilt carb on my motor, but I can only keep the motor running if I continually pump the bulb. It seems that the motor will not continue siphoning gas unless the fuel line bulb pump while running. Any ideas?

 

[MIKEY*2007]

Re: mercury 25hp outboard, later 1970's

how about fuel pump they won,t run with a broken one

 

[JB]

Re: mercury 25hp outboard, later 1970's

More proof that changing parts is the most used, most expensive and least effective troubleshooting method know to man.

Does that engine have a fuel pump? Guess what. It isn't working.

 

[shutterbugdm]

Re: mercury 25hp outboard, later 1970's

fuel pump is part of the carb, which I replaced with a remanufactured one out of Miami, FL. still did not run unless bulb continually pumped. Had the new/reconditioned one bench tested and it was a-ok.

 

[JB]

Re: mercury 25hp outboard, later 1970's

What mechanism operates the fuel pump? Did you bench test that, too?

Look into how the engine operates the fuel pump. That may be where your problem lies.

 

[Laddies]

Re: mercury 25hp outboard, later 1970's

To start with you have not given the right info Mercury Marine did not build a 25HP engine in the 70s. So start with the right serial number or carb number or something so it is possable to get you the right info. Its important as even after they started to build 25s in the early 80s they used 3 or 4 differant carbs and fuel pumps.

 

[shutterbugdm]

Re: mercury 25hp outboard, later 1970's

oops, that should be a 20 horse, not 25, my fault.
it is a 1978 20 hp Mercury, sn 5184088

all help appreciated.

 

[Laddies]

Re: mercury 25hp outboard, later 1970's

Ok, your fuel pump needs attention, while your at it you may as well clean the carb to as the pump is built on the side of the carb, heres a part breakdown that should be of help the Dia. and gasket kit is at the very bottom ot the page http://www.mercruiserparts.com/Show...81&bnbr=5&bdesc=CARBURETOR+ASSEMBLY,+COMPLETE

 

[Yepblaze]

Re: mercury 25hp outboard, later 1970's

The fuel line between the inlet fitting and the carb inlet, if allowed to, will abrade against a sharp edge there and cause it to leak.

This could cause a starvation issue. And would be evident if you squeeze the bulb with the hood off as a leak.

 

[shutterbugdm]

Re: mercury 25hp outboard, later 1970's

A rebuilt/remanufactured carb was installed but still same results.
all fuel lines were checked for leak, none detected.
could it be that there is a vacuumn leak, as this is what powers the
fuel pump?

 

[Laddies]

Re: mercury 25hp outboard, later 1970's

There could be a vacuum leak in the fuel line but the pulse for the fuel pump comes to the pump by way of the carb mounting flange, the wrong or improperly installed flange gasket will keep it from pumping.

 

[shutterbugdm]

Re: mercury 25hp outboard, later 1970's

giving up on it and trading in for a rebuilt 20hp johnson tiller, pull start, rebuilt last month with one year warrenty for $650. I will get $100 for the merc as trade. Tks to all for help.