1977 150 hp Mercury Outboard 2-stroke please help!!!?

Question

The motor starts fine, idles fine and has good low speed, but it has virtually no high speed. I just replaced all the wires and replaced the magneto and wiring harness. It only goes about 10-15 mph on full throttle. It's on a 17' boat, so it should be going alot faster. I would appreciate any suggestions!!

Answer 1

You have two problems, and one previous answer was partially correct. Unfortunately, you're probably going to have to take it to a reputable repair shop to get a full fix.

As mentioned before, your problem now is a bad ignition module (sometimes called a switch pack, or power pack) because it's basically an electronic ignition (not an old magnito type) that's triggered by little magnetic pickups positioned near the flywheel.

The module does many things that include cutting off spark to half the cylinders (on some larger engines) at low speed generally under about 1800rpm so the engine runs well at low speed and doesn't load up and run rough or die from trying to run too many cylinders with very little fuel to get the speed down.  More importantly, the ignition module greatly increases spark intensity and advances the ignition timing when you accelerate.  Depending on how it's damaged, it could be that it's not lighting up the rest of the cylinders as it hits 1800rpm (if your engine has that feature), or it's not advancing the timing or increasing the spark intensity like it should under acceleration and higher throttle positions.

Your second problem is what caused the first problem because, prior to around the mid-80's, almost no American made outboard had a voltage regulator.  Historically, most boats had so much added electronics that the conventional stator system couldn't keep the battery charged very well; and many times a battery would actually get too weak to start the engine if all the electrical stuff was running and the engine wasn't running at fairly high rpm to get enough charge from the stator/rectifier system.  

When major improvements were made in building much higher output stators, nobody thought about possibly overcharging the battery (duh) because just keeping one even halfway charged in the past was a problem.  However, with extended periods of running over half-throttle, battery voltage would many times get up to 18V or higher.  Not only did that cause short battery life and sometimes even causing them to boil dry, but the high voltage also began damaging many of the components in the ignition module which caused it to eventually fail.

I know for a fact that Mercury/Mariner put out a factory modification which added a voltage regulator for almost all medium to larger sized, 70's and early 80's outboards, and I believe Johnson/Evenrude did the same thing. Unfortunatly, it usually takes a service technician to install and wire-up the new rectifier/regulator module with the existing ignition wiring harness.

The parts alone are fairly pricey, so it's very wise to let a good outboard mechanic diagnose exactly what's wrong instead of trying to shotgun it yourself with expensive parts. Even though the voltage regulator mod will add a couple of hundred bucks, it's best to do it or you'll eventually be buying another ignition module - ouch!!

Answer 2

I would suggest to check your compression. I had a Evinrude that was doing the same thing and it turned out that I had low compression in the cylinders.

I read all of the other answers and they all make sense..

I would take a compression test first because it is so fundamental to engine performance and easy to do. Once I ruled out compression I would look at fuel and timing..

Good Luck..

Answer 3

Use caution squirting carb  cleaner in a running 2 stroke as you dilute the oil mix and risk scouring pistons.  It could be your stator going bad or just dirty carbs.

Answer 4

it sounds like the Power pack. IF you start out the motor sounds and runs fine but as you increase throttle the motor sounds like it is bogging down and wont go any faster ..... Its your pwr pack....

If it was your carbs you would have trouble starting the unit and running at low speeds.

IF YOU SHOULD NEED A LOWER UNIT I HAVE A BRAND NEW ONE NEVER BEEN IN THE WATER...I WILL SELL IT CHEAP.

You can email me at [e-mail] I can also get you a pwr pack cheap too brand new.

Answer 5

this may sound oversimplified ,but there are two things you must check.#1 -your lower unit for oil.

#2-The mercury propeller drive clutch is a rubber mount inside the propeller hub and in time that can begin to slip. If you have a tachometer, and the engine comes up to full 5000 rpm and you are going nowhere there is a good chance that is your problem.

If you don't get up to rpm, look to fuel and ignition and have a mechanic check the engine timing.

Answer 6

Choke not opening fully? Fuel lines or filter clogged....not vented properly....try removing the gas cap temporarily. Carb problem...stumbling, sputtering, engine missing or misfiring? May have to take it to a boat repair shop for diagnosis.

Answer 7

Hard to come up with a hard diagnosis without some more info but it sounds like you may need to isolate the problem some more.

When the engine is in the water and running full throttle in gear (you're going to need help for this obviously) take a can of carb cleaner and give a quick "blast" of the can down each individual carb ONE AT A TIME for less than 1 second.. (make sure to only spray the cleaner for a VERY breif time! you just want to giv the cylinder a "taste" of fuel.... don't go overboard or you'll wash all the oil from the cylinders and scar them!) If the boat suddenly "surges" forward or the RPM "jumps" that is a sign that the carb you just sprayed is not flowing the correct air/fuel mix. If you find that the engine "surges" when you spray any carb you have a fuel restriction problem to the carbs. Check for a bad fuel pump (if this is the case you should be able to squeeze the primer ball and see the engine RPM jump), clogged filter, clogged or varnished lines or tank, clogged tank vent (try taking the gas cap off and running it like that), or all of the carbs are varnished or filled with debris.

If carb cleaner has no effect use a timing light to determine if all of your cylinders are firing. To do this run the boat again under load and hook the timing light (inductive style) to the #1 cyl spark plug wire. Take the light and point it at your hand. You should see the light flashes on your palm. If you see "gaps" in the flashes or no light at all you have found a missing cylinder and need to hunt down an ignition problem there. Once you have done cyl #1 move on to #2 and so forth until you have tested them all.

Don’t forget the basics either. Have you checked compression? prop pitch? Checked for "leaks" in the crankcase halves?

Good luck!

Answer 8

What I would start off doing is replacing the fuel filter on the engine. It's a small filter that can get clogged and lead to no fuel getting into the engine. Also clean all of the fuel lines, including the ones inside the fuel tank. There might be carb problems. I would suggest running a concentrated formula of carb cleaner through the engine. Since it is pretty old, you might be looking at a total carb rebuild. If you can't diagnose, take it to a mechanic.

Answer 9

HI  FELCON. I have the same thing going on with my 1977 johnson im looking at temp. sending wire  (tan) comeing from power pack think it my be over heating,also going to change impeller i live in michigan so out of water till spring.also chk. over heating horn.it is under shifter.please e mail me if you find out what is wrong.wish i could be more help. please inform. [e-mail]       ps.here is one site to look in to.. www.theoutboardwizard.com  pss. please inform me thanks.

Answer 10

Check the prop hub.  If the prop has a rubber hub it could be starting to slip.  If it has a plastic hub(Flo-Torq II) take the hub out of the prop and check it for cracks or any other damage.

If this is not the problem, take it to a dealer as there could be hundreds of reasons for this to happen.  But the prop hub is the most likely cause.

Answer 11

CHEAK AND SEE IF YOUR CARBS GOT POWER PACKS . IF THEY DO THEN THE POWER PACK MAY NEED TO BE FIXED OR REPLACED . SOUND LIKE THE SAME THING MY BROTHERS BOAT DID "115 EVENRUDE  2 STROKE  "