20 Most Recent Mercury Mark 30 Hipo Outboard Motor (Mercury Marine) Questions & Answers


Ahhh Mercury electrical... always a problem. The charging system on a mercury is really simple. You should have 2 yellow wires coming from the under the flywheel and possibly a black one running with them. These are high voltage a/c. They run to the rectifier/regulator which converts the a/c to d/c and sets the voltage to around 14 volts. To test the charging circuit, disconnect the yellow wires from the rectifier/regulator, *CAUTION HIGH VOLTAGE!* hook up a meter, set to read a/c volts to the two yellow wires and crank the engine, be careful not to touch the wire ends while doing this, it could be a shocking experience. You are just looking for any voltage above 12 volt a/c. If you start the engine during this test you could see upward of 100 volts. If this test fails replace the charging coil under the flywheel, it the one with the yellow wires that you just tested. Chances are this test passed with flying colors.So plug it back in and test the rectifier/regulator. Disconnect the red wire(s) and set your meter to read > 12 d/c volts, there may be 2 red wires. Start the engine and test from the red wire(s) to engine ground, you should see >12vdc. 99.9% of the time this test fails. So replace the rectifier/regulator. It is the weakest link. They will fail for something as simple as a loose or corroded battery terminal.

Mercury Mark 30... | Answered on Jan 10, 2019


Start with 4.5oz. oil to a gallon gas

Mercury Mark 30... | Answered on Jun 23, 2017


Then change prop

Mercury Mark 30... | Answered on Sep 09, 2014


Your problem can be as simple as a bit of corrosion on the wire terminal on the starter/ solenoid .Also check switch and ground to the motor. A bit of emery paper and wire brush to clean all contacts and some dialectic grease on contacts afterwards will prevent future corrosion. If that doesn't help, you could have a " dead " spot on the starter. Then would need a replacement starter.

Mercury Mark 30... | Answered on Aug 12, 2014


not familiar with "Hipo" motor, but the early mercs had a filter under the fuel line connecter to each carb, then they started putting them under the intake of the fuel pump under a plastic cover.

Mercury Mark 30... | Answered on Dec 05, 2012


put it in forward gear. Drop the lower off by releasing the bolts and nuts holding it holding the lower on. (one is hiding under the back pick up screen)- some models had a plug in the back top of the exhaust/intermediate housing hiding an allen head bolt pointing down.

Once released, put a protector in a vise and clamp the lower to the bench.

2 screws or bolts will hold the water pump cover on. (the drive shaft runs thru it) Clean the carbon and rust off the drive shaft will allow the pump housing and impeller off the lower. Retrieve the funny looking key drive which runs the pump.

Inspect the shaft, the lower unit oil for water. and find all the pieces of the water pump impeller which may have gone places they shouldn't have.- including the outlet tube from the power head. Check this by putting a tube on the end and blowing- you should hear and feel the pressure in the exhaust and tell tale hole.

Now take the model number , the old pump parts to the marina for a replacement. Do a side by side comparison at the marina so you get the right stuff. Check the inside drive of the rubber impeller and see if they are exactly the same.

NOW- put the new wear plate / gaskets and drive key on, hold in place with grease. Slide the impeller on the key and spin the drive in both directions to be sure it has the impeller and will securely turn it.

Put grease in the cup of the pump housing to prevent dry start and help seat the impeller blades. Spin the shaft as you lower the housing in the pump so the blades all face in the right direction (clockwise). Screw in the bolts. Grease up the seal the watertube goes in and the spline end of the drive shaft.

Up the hole it all goes, now you only have to spline the shifter (it hasn't moved has it?) The drive shaft and the water tube all at the same time.

Check the shifter for correct position and bolt it down

Mercury Mark 30... | Answered on Jul 29, 2012


The tach wiring for an ignition signal should be connected to the negative side of the ignition coil.

Mercury Mark 30... | Answered on Dec 27, 2011


Spin Backward? that's not good. Would check the battery connections. If backward- you may have other problems associated with backward battery connections and ignition systems. If it's just an optical illusion- you should try to bridge the starter solenoid with a jumper to the big terminals and see if the starter is really bad or just a low battery. If your battery is down, your charge system on the motor may be giving you trouble.

Your starter when sitting on the bench and directly hit with 12 volts should jump substantially with the torque. If it just spins like a fan motor- it's shot.

If jumping the solenoid makes it work, thats the problem. But clean or replace the cable ends on the bat and solenoid first.

Just a note: you should be able to pull start that motor by wrapping a noted rope round the pulley on top of the flywheel. If you ever get stuck again. Just watch where the knotted end of the rope goes.

Mercury Mark 30... | Answered on May 04, 2011


Best not to do it as you will get maybe 2 mph. Also, I believe it is ******* to modify 1996 and later motors.

Mercury Boating | Answered on Sep 09, 2019


That cylinder isn't firing. Bad plug, or no spark to that cylinder. Swap the plug to another cylinder and check again. Then swap the coil to another cylinder.

Mercury Boating | Answered on Aug 22, 2019


Wow, a 40hp is FAR too small for a 16 foot anything except a bare aluminum Jon Boat with one person and a tank of gas!

90 to 110 hp is the recommended. I was guessing 70 to 90.
https://www.crestliner.com/fish-hawk/1650-fish-hawk

http://www.marineengine.com/boat-forum/showthread.php?289110-1999-mercury-40-2-stroke

WOT is normally 5000 to 5,500 WOT, but yours is struggling with the weight. There should be a coastguard regulation sticker in the boat with the Max HP that hull can take. You should have that motor or 10hp less.

The manual indicates 5,000 rpm for timing.

https://www.manualslib.com/manual/1198862/Mercury-40.html?page=9#manual

Mercury Boating | Answered on Jul 24, 2019


If you know the year or model number, you should be able to find the diagrams at http://www.crowleymarine.com. Otherwise call, I've known them to be really helpful.

Mercury Boating | Answered on Jul 12, 2019


Any outboard 2 cycle after 1965 will run on 50:1 approx 500ml or half a quart per 5 gallon tank.

Mercury Boating | Answered on Jul 06, 2019


Check the fuel filter for blockage and check the plugs for spark. If no spark, you could have bad coils. Here is a video on how to go through the checks.

Mercury Boating | Answered on Jul 06, 2019


Low oil alarm. They do suffer with a faulty low level alarm switch. Details in the link with some good videos

https://www.google.com/search?q=1991+75hp+outboard+has+a+constant+beep+alarm

Mercury Boating | Answered on Jun 24, 2019


(Carburetor Adjustment - Single S/S Adjustable Needle Valve)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

Mercury Boating | Answered on Jun 19, 2019


Sounds like the gas isn't flowing freely into the carb. Check to see if the gas lines are open, no obstructions. Also check the gas tank, I there is a screen on the gas inlet tube and that might be plugged.

Mercury Boating | Answered on Jun 16, 2019


There are some universal ones available, but I just stick my 9hp outboard in a bucket of water and flush that way.

Mercury Boating | Answered on Jun 11, 2019

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