I realize I’m not dealing with a powerhouse of a motor but I was getting much more out of my 35hp merc in the past. It seems like the engine is working hard enough, but that’s not translating to mph for some reason. Any suggestions on what could be going on, or what I should check first would be appreciatted. 
Matt
If speed is extremely reduces you may have spun the hub. What year is the engine.
I’d say it’s extremely reduced. The motor is a 1991, give or take a year.
Did you take the boat off the trailer? Leave the anchor/trolling motor down? Forget to replace your drain plug?
Am I a smart [censored]…..yup.
I have done all of the above, except the trailer, but that’s not the case this time. 
Pull the plugs out and check the compression………….
I’ll check the compression. How would I tell if it’s the hub? I’ve never had to work on an outboard before. If it is the hub are there two options…
1. Pull the prop and have the hub repaired
or
2. Replace the prop and hub
If that’s the case I’m thinking replacing may be cheaper, assuming I can do that myself.
Worn clutch dog?
Just a guess but I’ve had it happen on an older Johnson
that seemed to be running well enough to at least plane
out the boat…………but it couldn’t.
Does your outboard ever jump out of gear?
I’ve had this happen to a couple motors I’ve had. The engine would run good just like it always had but no speed, it felt like something was slipping or not connectng right. I got to where the problem was and it was the rubber vulcanizeing that holds the prop blades hub to the houseing that goes around the prop shaft. If it is this and to find out take the prop off and you’ll see a houseing that goes around the prop shaft and makes direct contact with it. Then you’ll also see the hub thats connected to the prop blades, if the prop (has) a vulcanizeing to hold both these parts together it will be between both these parts. Some motors have shear pins and some have the vulcanizing. When the vulcanizing is broken you have to get a new prop, the vulcanizing can’t be repaired, this is one of the downfalls to a prop like this.
I remembered hitting bottom on a rock or something and that broke the vulcanizing. The vulcanizing is rubber thats pressed under heat and pressure to bond both the prop shaft hub to the prop blade hub.
To check and see if this is it you can put the motor in gear with the prop blade still on the motor, with it not running ofcourse and then try to turn the propblade with your hands. You might have to try to turn it hard if its freshly broken but if this rubber is broken it will slip and you should feel it. Like said above some makes of motors have shear pins that are there so the prop isn’t damaged when something hits the prop. Some makes are vulcanized and you have to buy another prop, to date I don’t know of anyway or company that can repair them when this rubber vulcanizing is broken.
Matt, Make sure you have spark on both cylinders. If not swap coils from cylinder to cylinder…if spark is still nonexistant on the same cylinder replace the switch box..if the spark changes cylinders replace the coil. Also check the magnets on the flywheel..make sure there 180 degrees apart. Just a few things to check!
I recently purchased boat with 1988 35 hp mercury. Doesn’t seem to meet top speed.. I put in gear to check prop and it slips horribly. Do I replace prop? When I turn prop in gear it clicks
Quote:
I realize I’m not dealing with a powerhouse of a motor but I was getting much more out of my 35hp merc in the past. It seems like the engine is working hard enough, but that’s not translating to mph for some reason. Any suggestions on what could be going on, or what I should check first would be appreciatted.
Matt
Most likely culprit is slipping hub. See Mossy Dan’s post above, he is right on.
Other things to check would be making sure you have spark in both cylinders. Outboards run surprising well on only one cylider, it can really fool you.
Grouse
I know it’s been 3 years since the last post but I’m wondering if you resolved this issue. I’m having the same problem with my ’88 35hp merc.
Anyone else have this issue? I’ve checked compression, spark, fuel pump, fuel filter, cleaned the carb, checked for hub spin. I’ll be taking it out tomorrow for a spin to see how the afore mentioned works. My next step will be pulling the flywheel to check the stator and magnets, piston rings. my next option would be to check the reeds…don’t really want to go there but…
when was the last time the fuel hoses/squeeze bulb was checked for cracks and or leaks??
how about the carburetor,when was the last time it had a good cleaning along with removing the jets to make sure they are absolutely clean??
I ask as it doesnt take much crud to really limit what a motor will do and still seem like its working okay other than its low on power.
I would even go so far as to remove the top of the tank where your connection goes and check the pick up tube for pin holes and or plugging which will limit how much fuel gets to the motor.
another suggestion is to rebuild the fuel pump,kits run about twenty bucks or so and are easy to repair.
a motor if every thing mechanical is in good shape can only produce so much power for a given amount of fuel and still run with out going lean and burning a piston.
the last thing I will mention is how old is the fuel you are trying to run on??if it is over two months old,its stale and I dont care how much stable/seafoam or other additives are in it.
stale fuel will NOT make power,the gas we get today only has a shelf life of around thirty days before it loses its ability to fire properly.
I have seen the last issue I mentioned more times than I care to count,it gets worse if you had it out last winter early and still have more than a quarter of a tank of winter blend in it now.
the reason? its a winter blend that is designed to evaporate more readily in cold weather,it also has a lot of butane in it to aid in this and it really cuts into the fuels ability to burn properly when temps are above fifty to sixty degrees as it evaporates too fast,it will wreak havoc running wise in a warm environment.
two stroke engines are super sensitive to the quality of fuel you are putting into it,especially the older carburated ones,water cooled ones more so as they dont get as hot as an air cooled one.
good luck and let us know what you find out!! as I have said before,someone along the line will have an identical issue and your experience will help them out.
I took the fuel pump apart to clean it and did notice a very small tear in the diaphragm so I think rebuilding the fuel pump is a good idea. I just bought the boat about 3 weeks ago and have had it out about five times and it starts fine and idles really good. The boat just won’t plane out. My biggest fear is seazing a piston. I’ll be taking it out tomorrow to see if my thorough carb and fuel line/filter clean works. I’ll keep you posted. I only run non ethanol gas and my gas won’t sit for long until winter. Wish me luck.
rebuilding the pump is a must if the diaphragm is torn,it can not pump fuel like it should.
good luck!!!!
Got the boat out today and it ran with poor power. Back to the drawing board.
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