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Motor was running fine for 2.5 hours. I slowed for a no-wake…

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Motor was running fine...

Motor was running fine for 2.5 hours. I slowed for a no-wake zone and then could not get engine above 2,000 rpm under a load. Had to idle back to dock. Fuel filter was replaced last fall as part of winterization. Any ideas?

Mechanic's Assistant: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?

I am not sure what else he would like to know. 502 CI motor generation VI with about 300 hours. Fuel pump replaced about 3 years ago. IAC replaced last year. I am meticulous about care and maintenance.

Submitted: 26 days ago.Category: Boat
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5/28/2018
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 17,463
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 but do not see any kind of model information. Is this engine A Mercruiser, Volvo, Crusader, some other brand, or a home build? Do you have any kind of make/model/serial # info on the engine so I can look it up?

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Customer reply replied 26 days ago
Mercruiser 502. Generation VI. Motor Model(###) ###-####M1
Customer reply replied 26 days ago
Mark is my name
Customer reply replied 26 days ago
Motor serial no. S-0L085745
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Hi Mark Got it. Mercruiser engines are cataloged by serial number. Do you happen to have that number handy? Could you hear any popping from the intake manifold at 2000 RPMS? If you push it to full throttle, does the engine stall out, or does it just stay at 2000 rpms?

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Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Okay got the serial. Could you hear any popping from the intake manifold at 2000 RPMS? If you push it to full throttle, does the engine stall out, or does it just stay at 2000 rpms?

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Customer reply replied 26 days ago
No popping from intake but surely the motor is missing.
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Did you check your filters for water, or try running it on a portable gas tank yet?

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Customer reply replied 26 days ago
I did not try full throttle.
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Did you check your filters for water, or try running it on a portable gas tank yet?

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Customer reply replied 26 days ago
Engine does not quit running.
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Did you check your filters for water, or try running it on a portable gas tank yet?

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Customer reply replied 26 days ago
No. Did not check filter nor did I try a portable gas arrangement.
Marine Mechanic: Jason, Marine Mechanic replied 26 days ago

Bad fuel, water in the fuel, and water in the fuel filters would cause all of your symptoms. 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. Marine engines are very sensitive to the quality of the fuel. The rule of thumb is fuel has a usable shelf life of 90 days for a marine application. The catch there though is that is 90 days from the date it is refined, not 90 days from the day you buy it. Unless you live in south Texas or along the gulf coast The fuel can easily be a month or 2 old before you buy it. Adding fuel stabilizer will extend the fuels shelf life to 180. This is just the gas itself going bad that I am talking about. If there is any water in the gas, then obviously brand new gas will still be bad if there is water in it. 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. As part of this test you want to take your fuel filters and dump their contents into a clean glass jar, and look for water. If you get a little bit of water and some small trash out of the filters, you can re-use them. If you get lots of rusty water out of the filter, then you would need to replace those filters. Does that all make sense to you. I do want to make sure you are happy with my service before you go. If you had a further or more specific 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.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

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