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Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 07 merc 50 hp Efi 4 stroke, on a boat I just

Customer Question

I have a 07 merc 50 hp Efi 4 stroke, on a boat I just purchased
That I'm told only has 35 hrs on it, the boat had been winterized at a shop then sat for a full season of no use, the owner then sent it in for another service prior to selling it to me. I took the boat out for a try and could not get it to rev above 3000 rpm under load, would rev fine in neutral or reverse, I don't get any alarms from the guardian system, just one beep on key up. Since my test run I have replaced the water separator filter, inline filter, oil and filter change, leg oil change, checked fuel pressure, 44 psi. Checked batt voltage, grounds, throttle linkage, correct 12 pitch prop is on it. Engine seems to run good till the 3000 rpm mark then flattens off, no sputtering or misfiring just nothing more of the throttle , can't get on plane etc. Any ideas what might be causing this? I have not had the boat on diagnostics as local shops are booking 2 weeks away
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
Outboard model is 50 elpt 4 s serial 1c061901
Customer: replied 1 year ago.
I should add I removed the low pressure fuel pump to clean as well as the vapor separator both were completely clean, good diaphragms, clean screen on high pressure pump ect
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you.

Have you verified that there is good strong spark on all 4 cylinders that will jump a 7/16" gap on a spark tester?

Could you do a compression test?

Customer: replied 1 year ago.
I have not verified the spark jump but do have the equipment to do so, was planning on verifying both spark and fuel pressure again on the water under load to see if I could track down the issue, I have not done a compression test as of yet but all the plugs appear to be burning fairly clean and the same
Expert:  Charles replied 1 year ago.

Ok, let me know on the spark. You can also test the firing of it by using a timing light when it is at 3K rpm. you would just be looking at the light to make sure that it is a good flash and equal on all cylinders.

Customer: replied 1 year ago.
took the boat back out to the water today to test after my previous work, no change, came home performed a compression test, 138-144 between all cylinders, tried a second gauge in the hose and adapter in doubt of the engine being on the bottom end of the compression tolerance, same readings. Also noticed when pulling all the plugs number one cyl was wet with fuel, not real bad but wet while all others were dry, resistance tested as per manual number one coil and tested number two in comparison both tested within spec. The boat and motor are in immaculate shape not a scratch anywhere was purchased in 2010 new, I received some of the service paperwork as well as original invoices ect from owners, service paperwork says it has 35 hrs on the engine, have a hard time believing it would be wore out? Any further testing ideas you could suggest, number one plug wire tested slightly higher resistance than the others. I have not tested the spark jump or fuel pressure under load as I hoped, I may try the jump test yet tonight
Expert:  Charles replied 1 year ago.

For the compression, make sure that you have the throttle butterfly open. Being a four stroke, it needs to be open to get the air.

On the coils, how did you test them?

do you know how to do a test on the spark plugs using the multimeter?

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