Hey all, I've got a new issue with my old 75hp Evinrude outboard. Sometimes when I switch from idling to forward gear, then wide open throttle, I get some vibration and wide open throttle only gets me up to around 7mph. Usually gets up to around 35mph with my current boat. Usually, if I leave it in wide open throttle for a minute or so, it’s like something “catches” (nothing audible or anything), and it’ll ramp up and run fine like normal. Any thought on what might be going on? New plugs at the start of the year. Also, I've only noticed this happening when other people are on board with me - could the issue have something to do with load? I'm thinking not, but figured I'd throw that info. out there too. Could there be a spring or something somewhere that's catching on something, then jumping to the position it should be in? That's kind of what it feels like is happening. There's no clunking or anything when it switches from "limping around" to normal WOT.

Also noteworthy - during the time it only runs around 7mph in WOT, the motor is not revving up like normal either.

Have you cleaned the carbs? Those 3cylinder omc motors are pretty much bullet proof with dirty carbs being the most common issue.

I've not yet touched the carbs, but have been thinking about it. Hoping for others' thoughts & suggestions as well.

If it's just not revving up, it's probably a carb issue. If it's misfiring,you might be looking at an ignition issue. I don't know much about boat motors, bit in the automotive world, when I have an old engine that wont rev, my first thoughts are a.carb issue, ignition timing, or maybe a plugged up exhaust.

Sounds like it is starving for fuel, and those triples like their fuel - a lot!! As Warrior states, clean the carbs...

Are you saying the RPMs are normal, except for vibration at WOT but boat is only doing 7mph?

Easy way to find out is to run it with wide open throttle with the cover off and then squirt some fuel into the air box. If it picks up right then ya need to clean the fuel make it happeners if it don't. its timing or maybe getting a tad low on compression.

I have no tachometer, but the RPMs sound right for 7mph when it wants to run that way, and the RPMs sound right when it is running normally at 35mph. Does that make sense? The speed and RPMs seem to make sense together, regardless of the speed. The vibration that I'm seeing is only when it's low RPM and low speed, but WOT. The vibration stops after something changes and the RPMs and speed pick up.

Sorry, I re read your post. Not revving up.

I was thinking it was a prop issue when loaded.

You could sure try adding Star Brite "Startron enzime fuel treatment" it has helped many fuel issues with my older stuff, outboard, snowmobiles, chainsaws. I use it in everything.

Another thing, when you get it back right quit using pump ethanol gas. Those motors were set up for pre ethanol pre summer/winter blends leaded gasoline. Now the lead isn't an issue since it's a two stroke but the ethanol and other additives are.

Original carbs?

Older carbs often used a cork float in the bowl and over time the floats got saturated and erratic in function eventually failing. I've also seen plastic floats cracked (no idea how) and full of fuel. Of course if you dig this far in you've got the needle valves and seats open for inspection.

Then there's the reeds.

I bought this boat and motor from my in-laws three years ago. They ran ethanol gas in it, and I've seen the fuel hose destroyed because of it. When I bought it from them, I replaced the hose and primer bulb, added an inline fuel filter, and have had to replace the starter.
Since I've owned it, I only run premium. Original carbs - thinking of doing a complete rebuild on all three. Where are the reeds, and what should I look for?

This motor has always been a bit cold-blooded, even on warm summer days. Almost every time I want to move to a new spot, i need to use the warm-up lever for a minute or two while I'm reeling rods up and stowing the trolling motor. Think a carb re-build would help with these issues as well?

On the advance spark lever under the flywheel they wear, check that if it is flat or not
sometimes the spring gets tired and does not hold it in place.

the pins in the jets get a little white crust on them, polish clean

I have a bit older 75.
Mine did the same thing. Coil packs made a weak spark.
One out of three had a spark jump almost a half inch.
The other 2 would fail under 3/16 of an inch.
I replaced them along with the plugs.
Runs great and sips gas.
I have ran it on erie pushing an old 16 starcraft.
9 mile run out and trolled for almost 6 hours on 6 gallons of gas

Fuel sipper for sure.

Run some seafoam through it as well.

Coil packs was the other thing I was thinking but was drawing a blank on what those electrical thingys were called.

Your loading up ideling and fouling a plug. Rebuild your carbs.

Many of those motors have an auto choke. It operates off a small thermostat that usually goes bad so the choke is flipped on even when starting warm. This “loads up” the motor and it takes a while to clear or ends up fowling plugs. With the cover off, turn the key forward without cranking and see if the choke lever on side of carbs moves, you should be able to hear it as well. Then check it again when motor is warm, it should not be activated if warm. If it moves when warm the choke thermostat is bad.

My old 85 Evinrude had that choke system and thermostat was stuck. Was real hard starting when warm because it would automatically choke even when it didn’t need it. I bypassed the auto choke and only use manual choke switch when cold and it made a huge difference. Starts great when warm now. It’s a simple fix, if you need to do it let me know and I’ll find the link. It’s a matter of moving auto choke wire to manual choke post so it only gets a signal when manual switch is flipped.

This could be your problem, motor could be running like crap until it clears out the load up from excessive choking.

Here is a service bulletin about how to disengage the auto choke. They had trouble with them and went back to regular manual choke. When I did this to mine it started great warm. Before it cranked and cranked.

Is the circle area in this picture in the ignition at the remote, or back at the terminal strip in the motor housing?