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I have a 2016 Mercury 150 4 stroke on a 2016 Tritoon. The…

I have a 2016...

I have a 2016 Mercury 150 4 stroke on a 2016 Harris Tritoon. The motor has ran well all season till this past weekend. I normally cruise at 18-20 mph with 3700-3800 rpm's. And it will run wot at 35 mph with 5100 rpm's. It would cruise at the same rpm's normally but sounded like it was bogging down. This past weekend it would only run 4500 rpm's at 25 mph. Also seemed like I burned alot more fuel than normal. I thought i had some bad gas so i dumped 2 cans of seafoam in the tank. That didn't help. Could a dirty fuel filter cause these issues or is it something more serious?

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Answered in 7 minutes by:
8/21/2017
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 17,374
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hello my name is ***** ***** am I speaking with? I read what you wrote. It could be any number of things. How old was the fuel you were trying to burn? Have you tried running the outboard off of a portable tank full of brand new fuel yet? Specifically when was the last time the outboard ran correctly?

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Customer reply replied 10 months ago
My name is***** have around 135 hours on the motor. I store my boat at the marina and we ran it a month ago and it ran great. I have never replaced the fuel filter. The fuel was about a month old and its non-ethanol. The tank was full with 33 gallons and I burned around 30 Saturday. I filled it back up yesterday with new fuel and the motor ran the same. At wot it sounds like its bogging down and just wont get up to speed.

Hi Brett. Okay got it. These engines are fairly complicated, and I do not know what you have for tools or outboard knowledge in general. Did you have any questions that you specifically wanted me to answer, or would you prefer if I explained how we would troubleshoot this type of issue in the shop?

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Customer reply replied 10 months ago
yea how would you troubleshoot this problem.

Okay give me about 10 minutes to get you an answer typed up.

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Customer reply replied 10 months ago
sounds good thank you

As simple as this sounds you always start by running it off of a different fuel tank, like a small plastic portable tank. Half the time there isn't anything wrong the motor itself, but rather something wrong with the boats fuel system. This can be a pinched or collapsing fuel line, bad or old gas, or a bad anti siphon valve. Marine engines are very sensitive as to the quality of the fuel, and if any part of it is over 90 days, the fuel itself is always going to be suspect. This is a pass or fail test, and the engine is either going to run better or it is not. If it does run better, on this portable tank, first change the anti siphon valve and retest with the engine hooked back up to the boats fuel tank. If it goes back to running poor on the boats fuel tank, that tank will need to be pumped out. Bad anti siphon valves are a common problem, when they go back they create a blockage and restrict the amount of fuel that flows to the engine. If the engine does not get enough fuel it obviously will not make full power. Click this link, this explains more on the anti siphon valve and why they go bad. http://www.sterndrives.com/anti-syphon-valve.html. On this anti siphon valve there is an inlet side and an outlet side. The inlet side faces the fuel tank, the outlet side faces the fuel line. When the engine runs, the fuel pump creates suction. This suction pulls the check ball off of it's seat and fuel is allowed to flow around it. The problem with this is over time the spring in the valve will get weak or simply break. When that happens the check ball will be free to jump to the outlet side of the valve and create a blockage/restriction on the outlet side of the valve. If the spring is simply weak and not broken, this will more or less happen at random. Click this link for a picture, it will make more sense once you see it Http://imgur.com/a/tpq4H. The anti siphon valve itself is located at the fuel tank, where the fuel line connects. If you pull the fuel line off the tank you will see a hose barb, that hose barb is the anti siphon valve.

2. Change all fuel filters and retest.

3. If no change, then compression testing the engine is next. Your results need be about 100 psi or better on that engine, all cylinders should be within 10-15% of eachother. If you get below 100, then the engine is worn out or has mechanical problems, and you might as well stop your troubleshooting here, as there is nothing you can do to an engine with low compression to make it run better. From there you would perform a valve adjustment (or in this case check your pushrod lengths) and see if the compression comes back up or not.

4. Spark test. This engine uses pencil type coils, so the only way to check for spark is to get an adjustable gap spark testing tool, set the gap on that tool to 7/16ths of an inch, hook the tool up to each coil, crank the engine over, and see if spark jumps that gap or not. If it does not, you likely have a bad coil.

5. Hook up a fuel pressure gauge and check fuel pressure. It needs to be roughly 43 psi. If it's low, the fuel pump is weak or the fuel supply module has a sticking float and the pump is not calling for fuel. Make sure you do this after you do #1 and 2. If that anti siphon valve is bad that will cause low fuel pressure because the fuel pump would be struggling to pull through that restriction/blockage that a bad anti siphon valve creates. Same thing with the filters, if they are clogged the fuel pump will struggle and the engine will show low pressure.

6. Lastly, if you do all of the above steps and still do not get any kind of result, you have gone as far as you can with basic hand tools and the engine would need to get hooked up to a scan tool. Does that all make sense. I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Please note that our question sessions never close out, so if you need to come back later down the road with follow up questions to the issue, you can do so at any time, even after putting through a rating.

Thanks in advance, and good luck
Jason

Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 17,374
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Customer reply replied 10 months ago
Thank you for the steps on trouble shooting the problem. 1 last question on these motors i would like to turn more rpm's. Mercury recommends this motor should turn 5000-5800 rpm's. I'm at the low end when running right at 5100. Is there a way I can turn up the rpm's or does a dealer have to program the motor to adjust.

What you would actually need to do is change the propeller pitch. For every inch of pitch you go down, the RPMS on the engine will increase by 200. For example. If your current prop has a 17 pitch, and you drop that down to a 14 pitch, the RPMS will jump 600 from 5100 to 5700.

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