Boat motor issue

[4R Daddy]

I'm hoping one of you helpful guys that know something about outboards can give me a hand with my boat. I put an 85 hp mercury on my 1860 jon boat and it seems like the thing just isn't putting out enough power. It won't pull out of the hole unless one guy is up front and I'm driving. It may be all it can do but I'm not boat savvy enough to know. Someone willing to jump in and go for a ride and tell me what to do?


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[4R Daddy]

I'm in Flower Mound, btw.


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[panhandlehunter]

That's plenty of motor for that boat. It could be a number of things. Could be carbs, could be motor height. Who knows. That's why I hate boats. Lol. I had a similar issue with my boat recently, dropped it off at the shop and got a tune up, cleaned the carbs, new plugs and new gas and she runs great now. I'm also not a mechanic and if I have an issue I just take it to the shop.

[Walker]

Easiest, first thing to do is a compression test on all cylinders. Since it starts and runs you are looking for a cylinder that is way lower than the rest. If all is well new spark plugs. I dont care what.plugs are called.for, put champion L77JC4 gapped at 030 in her and see.what happens. If that doesnt work then theres a 99% chance the carbs are fouled.

[Rat]

You need to get max RPM and see if the motor is hitting max RPM. If it is, it could be a wrong pitch/diameter on the prop; depending on what it came off of it could be the wrong prop.

I have a 150 on my 17 footer, I don't know if yours is under powered or not, but I don't think it is.

Compression would be a good place to start, but don't forget about fuel and spark.

[pervis]

Dirty carb, prob not firing on all cylinders. Prob replace the coils for good measure. There s a number of things to check

[manwitaplan]

You need to get max RPM and see if the motor is hitting max RPM. If it is, it could be a wrong pitch/diameter on the prop; depending on what it came off of it could be the wrong prop.



I have a 150 on my 17 footer, I don't know if yours is under powered or not, but I don't think it is.



Compression would be a good place to start, but don't forget about fuel and spark.

This right here is the thing to do. What is your max rpm wot? What prop is on the boat? That's where I would start.


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[Hart8]

Sounds like the wrong pitch on the prop to me..Once you plane out does it run alright?

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[Hart8]

Check Mercury's website for correct pitch to h.p...I was having similar issues a few years ago,and dropped from a 23" to a 19" and all,was right.

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[doright]

If it runs good with more weight in the front of the boat it sounds like the motor is mounted to low. Try raising it up.

[Mambajeep]

IF the motor is running properly, motor height, the right prop (the more blades the better hole shot) and adding a hydrofoil ( they work well on metal boats)

[tminc]

yes a jack plate will help on the hole shot

[muzzlebrake]

As mentioned above, do a compression check first. Easy things first. You would want to see even compression on in all holes, 100 psi cold cranking or higher. If all is good there then on to the plugs, carbs and fuel system.
Prop pitch should probably be 13-15" depending on lower unit for decent hole shot. WOT planed out should be around 5500-5600 if propped correctly and assuming the motor is at correct height. Center line of prop shaft should be 3.5" below bottom of lowest part of transom.
I have compression a gauge and live over in Euless if you need help with compression test.

[BarW]

All above could be the culprit, personally unless you are only running ethanol free fuel I would lean toward the carbs. Something cheap, quick and simple to try is load your tanks and fuel system with seafoam additive and see if performance improves. Another idea that has not been mentioned is a pin hole in the fuel lines causing a small vacuum leak hard to detect but can cause the same symptoms because the engine is starving for fuel. I also had a fuel line separate on the inside once, line was partially blocked. I changed the fuel line grasping at straws and when the engine worked normally I cut the line in two and found the problem.

[4R Daddy]

Thank you for all the ideas. Here's more info

I have checked the compression. It is above 120 on all cylinders. When I bought the motor, I replaced the switch box right away as the shop told me it was bad and 1 cylinder wasn't firing. It starts ok but at about 1/4 throttle is does run rough. I've actually been wondering if the motor isn't sitting too high because I can't trim it up much or it starts missing the water(I'm sure there's a correct term for this but I'm not nautical). I will measure the distance as mentioned. I will also verify spark next.


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