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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3929
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Have a question about my honda outboard. It's a 4 stroke

Customer Question

Have a question about my honda outboard. It's a 4 stroke 90bfa. The motor idles perfect. When I run it at full throttle it's only 3-3.5 RPM about 32 mph. While running at full throttle it will jump up to around 40 MPH on its own. I can also hear so pop noise coming from engine. I changed the fuel primer bulb assembly and spark plugs..... recommendations?
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

Hello my name is ***** ***** am I speaking with?

Popping from the engine is a sign of abnormal fuel burn. A couple of things can cause that including but not limited to a sensor issue, low fuel pressure, dirty fuel injectors, sticking fuel injectors, old gas, and water in the gas.

How old is the gas in the boat that you are trying to burn now?

Customer: replied 1 year ago.
I've went through a couple of Tanks over the last few weekends it runs really really great when it does. At Full Throttle it will never be below 32 mph. It's the sudden jolt of RPMs and speed is what concerns me. I tried seafoam and it did not help at all. Over the last few weekends I go through a tank every weekend so there is constant fresh gas in there. Sorry my name is Justin
Expert:  Jason replied 1 year ago.

Hi Justin,

Can you do a compresion and spark test on the engine? If there is something else going on like a bad head gasket that can do it as well.

Customer: replied 1 year ago.
I'm pretty mechanically inclined but that seems a bit out of my reach I may have to put it in the shop for that. Also now that I think about it the throttle response is not up to par when starting to take a plane. When I really start to get on the throttle is one of all the popping noises start
Customer: replied 1 year ago.
Also it has extreme fuel burning going on.
Expert:  Charles replied 1 year ago.

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

With the power loss, you are not running on all 4 cylinders. This could be cause by one of the already mentioned items or the filter in the fuel line is clogged, or the last one would be debris in the carb bowl that is blocking the jets, and then moving sometimes and allowing you to make full HP. The excessive fuel burn could also be caused by this. first check that I would do in the shop is to inspect the spark plugs and possibly replace them then run the engine to see if that made a difference.

Customer: replied 1 year ago.
I've already replace the spark plugs and I replace the primer bulb fuel assembly and it made absolutely no difference
Expert:  Charles replied 1 year ago.

Check the fuel filter and then drain the carb bowls. try and catch the fuel from the bowls to see if there is any debris in it.