1970 vintage 115 hs looses prime

[Camo]

My 1970s vintage Mercury 6 cylinder ("tower of power") 115 horse motor will not start till I squirt mixed gas into the two (of three)choked carborators. It may start again later without it if it isn't too long. But any lenghth of time and more manual priming is required. Sound familiar? Where do I start? Something like a carb diaphram gasket or??? Is it hard to fix for a motor dummy like me?<br /><br />Many thanks for any help...

 

[mellowyellow]

Re: 1970 vintage 115 hs looses prime

there are check valves in the fuel pumps as well<br />as well as the primer bulb that are supposed to help keep<br />the system primed. I'd start there.<br />good luck,<br />M.Y.

 

[Camo]

Re: 1970 vintage 115 hs looses prime

Everything takes me a while...Thanks for the response. I want to do this project BEFORE ice out this year, so here I go...Are there three fuel pumps on this "Tower of Power"??<br />I presume I need to take the pumps apart to check the check valves in them. These are what they call diaphrams? Are they located next to the carbs?? Any other secrets or pitfalls to taking them off and putting them back together I should know about??<br /><br />Thanks in advance!

 

[rickdb1boat]

Re: 1970 vintage 115 hs looses prime

Check to make sure the choke flaps are completly closed. They need all the fuel they can get when starting cold. Love those old cold blooded Mercs!! Had a 67' model and it was difficult to start also, even when warm after stopping for a half an hour I had to choke it to get it going almost everytime. The electric choke may not be working, so check it out. Also, replace the primer bulb and fuel lines from tank.

 

[WillyBWright]

Re: 1970 vintage 115 hs looses prime

You probably have two fuel pumps. Get two complete fuel pump rebuild kits from a Merc dealer and rebuild them. Don't bother diagnosing any of the parts, just rebuild them. They're not rocket science. You'll just need a few common tools. If the fuel lines are still original, replace them all. You'll probably have to get fittings and hose because I doubt there are replacement lines available. Everything for that is available at your local auto parts store or the Farm & Barn.<br /><br />Then choke, choke, choke. These things drip fuel from the carbs before they get enough gas to start. Very dirty motors!

 

[Clams Canino]

Re: 1970 vintage 115 hs looses prime

And make sure it is trimmed all the way in before starting it. Make sure the choke is ON during the cranking. <br /><br />Very cold blooded motors.<br /><br />-W

 

[Camo]

Re: 1970 vintage 115 hs looses prime

Many thanks you guys. I have the motor trimmed down when I start, the electric chokes click with authority (although I haven't actually watched them close - but I will), I replaced the primer bulb, so, some of this I've done. I'll do more. The fuel pump rebuild might be the next logical plan. <br />Many thanks!<br /><br />Where is/are the fuel pump/s located?

 

[mellowyellow]

Re: 1970 vintage 115 hs looses prime

pumps are not next IMO marty... first check all<br />lines/connectors/clamps/pick up etc. for air <br />leaks or bad connections. if air is allowed in,<br />you will also lose prime.<br />inside the boat looking at her, there are 3 pumps<br />on the left side. easy access rebuild kit is<br />just a gasket and pump diaphram. I would install<br />new ones just as reg. maint., but start at the beginning...<br />good luck,<br />M.Y.<br /><br />PS. getting a manual is actually the v.first step...

 

[Clams Canino]

Re: 1970 vintage 115 hs looses prime

Depending on the year, it's *2* pumps on starbord side of the block , OR in 74 and up, one single pump on the starbord side mounted to the belly pan.<br /><br />I agree that(fuel pump) should not needly be next. A good trick is to squeeze the ball till the water around the motor turns colors - LOL. And make sure the choke flappers are actually flapping.<br /><br />-W

 

[emckelvy]

Re: 1970 vintage 115 hs looses prime

My old 100 usually wouldn't start until you squeezed the primer rock hard and then let fuel blow past the float needles into the carbs. Maybe another thing to do is richen up the idle mixture a bit. The warm-hard-starting thing sounds like a lean condition, usually if they are cranky on re-start after warmed up the idle's too lean.<br /><br />Try moving each idle mixture screw 1/8-1/4 turn CCW (rich) and see if it improves. Make more small adjustments and see what you get. <br /><br />You can also warm it up and adjust each carb in the water in gear. Set each idle mix screw to the rich side of the adjustment range.<br /><br />If you're bogging on acceleration from an idle, that's another sign of being too lean. The old inlines are hard to make happy, if you get them rich enough to keep them from being cranky, they're too rich to idle cleanly. <br /><br />Then if you lean them out enough they'll idle clean and be cranky again on starts & takeoff. <br /><br />Best to live with a bit of a rich idle and then it's all good.<br /><br />If it's not the mixture adjustment or other carb problems such as maladjusted float levels or trash in the carbs, you may have something else such as loss of crankcase vacuum/pressure from a bad crank seal, or loss of compression from bad rings. Done a compression check lately?<br /><br />HTH & Good Luck........ed