Mercury 75hp Outboard Question

[Guppy35]

Every time i take this boat out, the same thing happens when trying to start this motor (Mercury 75hp).  It cranks and acts like it wants to start, but it will take many turns of the key before it actually fires up (sometimes it will start up but only stay running for a few seconds).  Then for one reason or another, it will start up and stay running without problems, even on idle.  I use a kicker for trolling, and if i decide to pick up and move, i can then turn the key (to the big motor) once and have it fire right up every time.  But it doesn't matter if it's early Spring, or middle of the Summer, it ALWAYS takes several minutes to get it fired up at the beginning of each trip.

 

Now i know this motor hasn't always been taken care of or serviced the way that it should have been, but now that i have it i'm trying to get it running better and take care of it a little better.  Any ideas what i should take a look at on the motor to get it to fire up better at the beginning of each trip?  Does it sound like a carburetor issue, or something else?  I'm not looking to rebuild the whole motor, as i don't have the money for something like that.  Just trying to figure out a few little things i can do to improve it.

 

Thanks!

 

[Sk8man]

I know there are quite a few things that it could be but I would first check your battery because if it is weak and is discharging when not in use it may be "marginal" for starting the engine and then after your alternator puts some juice back in it has enough to start it up more easily. Also check and clean the battery connections. The status of your plugs is also a question and for an older motor the possibility of a carb rebuild is not out of the question either especially if it has been run on ethanol gas. Good luck with it Sean.

[Guppy35]

Thanks for the response Les.  I don't think it's the battery, because I just replaced the battery last year and it didn't seem to make a difference when starting the motor.  I will check and clean the connnections again though, never hurts to have a better connection.  I'm not sure when the spark plugs were last replaced on it, so maybe i will buy a new set of plugs for it as well.  I'm almost positive the motor has been run on ethanol gas for the majority of it's life, so i'm thinking that a carb rebuild would probably make a difference (if even just a little bit).

 

I replaced the impeller on Saturday, and i'm glad that i did too.  The old one was eaten up pretty bad and i'm sure it wasn't doing anything to properly cool the motor.  I know that issue probably doesn't mean much when talking about starting the motor, but it is nice to know that there is a new impeller in it now.

[Sk8man]

Good thing you caught the impeller situation. I'd do just one thing at a time to see if it corrects things e.g. plug check and replacement if necessary then consider other things so you'll know for sure.

[Guppy35]

Good idea, thanks for the advice!  I'll start by replacing the plugs and see what happens from there.

[henrybud]

Trouble shooting wise the first thing is the fuel.  Is it sometimes starving for fuel and sometimes not?   If after all this cranking it's not getting flooded (smelling the gas and the sheen on the water) and not starting, you're starving for fuel.  The first step is to check your bulb and fuel lines.  I've had, through the years, faulty bulbs that seemed to be holding pressure after pumping them up but actually they were faulty.  I would try going through your fuel lines and bulb carefully and try swapping it out for a new bulb.  Relatively cheap too. 

 

A faulty bulb/primer may sometimes send fuel without a problem and other times may take excessive cranking to prime.  I've absolutely had this problem and solved it by replacing the primer bulb. 

 

The next thing I would look into is the ignition on your merc.  My older mercurys that I've had had low AND high speed ignitions.  One may be faulty.  Can you let me know the year of your motor so I can look into it some more.  I love stuff like this!  Larry

[Guppy35]

Larry,

 

Thanks for the additional tips!  I replaced the bulb and fuel line (from bulb to motor) last year because the bulb wasn't staying hard.  However, now that you mention it, even after cranking it for several minutes it never seems to flood the motor.  In fact the way it sounds it seems like maybe it is starving for fuel.  I'll have to look into it further and see if i can find anything wrong with the rest of the fuel line and may have to replace the rest of it.  The motor is a 1984 model year / 4 cyl 75hp

 

Thanks for looking into it, i appreciate it!

[oldkevin]

I have found also the fuel pump diapham might be bad. the ethanal gas makes them stiff and they don't want to pump the gas to the carbs

[muskiedreams]

I have a 1990 75hp mercury but it is a 3 cyl with oil injection. I have repaired many problems over the years. but your description doesn't sound like any of the problems I have had. Plus your motor is probably different than mine. It does sound like it might be a cold start problem. Mine has a prime solenoid that is activated by pushing in on the key when cranking. I have to keep pushing it in for short periods of time while keeping the idle speed up until it warms up a little. I usually only need to do that for the first time I start it and sometimes just a little when starting it later on if it has not been run for quite a while because the engine block holds heat for quite a while. The prime solenoid directs extra gas directly into the carbs when the engine is cranking and the diaphragm fuel pump (which run off of engine vacuum) is running. If you have a prime solenoid, you can check to see if it is energized by holding a screwdriver by the coil to see if there is magnetism when you push the prime (key). You can also check to see if the  prime solenoid valve is opening by removing the hose from it's outlet and look for gas coming out when you crank the engine and press the prime. I doubt there is a problem with the fuel pump because that would cause it to have fuel issues when it is running, especially at high speeds. If spark plugs or ignition was a problem, it would flood, you would probably smell gas and the plugs would be wet. If it runs OK and idles OK after you get it started, I doubt there is any problem with the carbs. Hope this helps.

[Guppy35]

Muskiedreams - Thanks for your input, that is very helpful information as well.  I guess i kind of told a lie when i said in my original post that it "idles" fine after the first start of a trip.  I can go about 3mph with it without any issues, but if i try to go slower than that or have sit in neutral, it usually stalls out fairly quickly.  That happens whether the motor has been running for 1 minute or for 30 minutes.  As far as the prime solenoid, i think i have the same setup as you do.  In order to prime it when starting, i also have to push in on the key while cranking.  I haven't had a chance to check it out since your post, but i know in the past that i can hear it make a single click sound as i push the key in.  Does that mean that the prime solenoid has magnetism, or should i still check that out?

 

Sorry for my lack in knowledge on these things, i never really learned much about motors/engines when i was younger, so i am trying to learn as i go here!

 

Thanks again for the responses.

[guffins fisherman]

X2 on fuel problems. More than likely that motor has an ignition that energizes a primer. Turn your key to on, not start, and if it pushes in, you should hear a click coming from the primer(usually right next the fuel pump or carb) when you push it in. That click is the primer activating. If that is not working, the motor would start hard. You can actually hold it in while cranking it over and give the motor a little extra fuel. Those two strokes lime fuel to start.

[muskiedreams]

Does it run faster ok. Does it accelerate ok and get up on plane with no problem or hesitation.

[hawkeye625]

I had a 1990 140 Johnson that did the same thing.  One trick that helped mine start faster, prime the bulb til hard, turn the motor over for a few seconds, go back and reprime the bulb til hard again.  Mine usually started after that sequence and would fire right back up after trolling.  My buddy now owns that boat and the trick still works.  I'm guessing there is a pin hole in the fuel supply somewhere but could never find it.  That motor would fine if we used it every day, leave it sit for 2 weeks and you'd have to go through the same thing.

 

Definitely change plugs.  I'd get in the habit of doing that every spring.  Relatively cheap and 2 strokes like to foul plugs, especially if you run them at low speeds. 

 

I'd also recommend running the boat at home on muffs the day before you plan on fishing.  It never hurts to check things out in the driveway, also helps speed up the start in the morning.

[Guppy35]

Guffins - It does click when i push in on it, and historically i've always had to hold it in as the motor cranks (the first start of the day).

 

Muskiedreams - Yes, once it starts up in neutral, if i give it trottle it will take right off and not have a single issue at higher speeds. 

 

I think i'll replace the spark plugs before i do anything else.  That may not be the problem, but it's a quick fix and at least i'll eliminate that as a potential problem.  Hawkeye, i will have to try the start-up procedure that you mentioned above and see if it works for me as well.

 

Thanks again for all the advice!

[Little Crappie]

I've even purchased new bulbs that were faulty.

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[BAZOOKAJOE]

Replace the plugs and run non-ethanol gas! My 90 hp Mercury 2-stroke starts much easier with non-ethanol. Idles smoother and runs better!!

[Guppy35]

If i start using non-ethanol gas, do i need to get rid of the gas that is currently in the tank, or just start using non-ethanol from now on?

[BAZOOKAJOE]

No

[llabarr]

Had problem with Suzuki ,would start hard but once started would run over 3 mph fine. Changed plugs and nothing changed, so I pulled plugs to look at and found 1 cyl. Was not Evan getting fuel. Pulled carbs, cleaned and ran new line. Thing not only starts easier and idles down but I gained a ton of power. Would change plugs, run it for a little bit and look at them. That would be my first step. Will tell you alot. If not good at reading them ,mark plugs for each cyl. And take them to marina.

[old man]

Could be a sticky needle/seat. Rap on the carbs near the inlet before starting. If that helps you found the problem. Replace or possibly just clean them.

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[SylvanTroller]

I would rebuild the carbs being extremely careful to clean out all of the small orifices. Post clean up and rebuild use ethanol free gas only. Best of luck, my old boat had a 90 yammy that did the same thing.

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[Has Been]

I have a 86  35 hp merc  2 stroke. When is last time carb was rebuilt ? Mine did kind of same thing.  Is your hose the original  silver . Mine broke down inside & sent particles to carb.Also check fuel pump diaphram . Whenver I clean out the carb , it fires right up after. Then adjust jets, Last time it did it I was camping. Took off Carb, sprayed WD 40 in the end & dumped it on a white napkin. A tiny piece of funk came out. Thats all it takes.

 

 DO NOT....... repeat ........... DO NOT use ethenol gas. I have driven 35 miles to fill my tanks. Learned my lesson the hard way. My buddy did also.

 

Also my nephew down in Naples FLA works with a Marine mechanic. He gets a gallon of gumout &  imerseses whole carb overnight , washes w/ soap & water & blows out w/ air gun. Fixes carbs others don't.Does it all the time.

 

 Might be time to take it to a mechanic before the season starts . Could be money well spent.

Edited March 24, 2015 by Has Been

[rolmops]

I had a 1985 75 horse merc,with the same problem. It is easily solved. Your remote control has a lever for neutral idle which doubles as a choke. If you bring that lever up before you start and then start it will work just fine. Let the engine run at medium rpm to warm it up and you should be alright. As for the engine stopping at very low rpm,mercury made those engines for racing ,not trolling. Your solution would be a smaller prop so you go slower at a slightly higher rpm. As for ethanol gas or regular gas,you will find that performancewise on this engine,it makes absolutely no difference except for paying an extra 40 cents per gallon.Just dump some seafoam carburetor cleaner/stabilizer in every third tank or so and you will do just fine,although it better for these engines to use 89 octane instead of 87. What may improve your engine performance is decarbing the engine. Buy a spray can of "seafoam" and follow the decarbing directions for 2 stroke engines.This  improves compression and cleans out the carburetor during the process.

There is another thing that in this cold weather is very important and that it a high quality fuel hose and pump ball. The Walmart version turns very stiff and hard in cold weather,while a high quality ball remains easily workable.

Edited March 24, 2015 by rolmops