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Honda BF150 erratic running at high RPM

S

Square Head

New member
I’ve got a 2015 BF150, with 190 hours, that will run great at WOT for 5-10 seconds intermittently. It will then drop to 4500 and remain there, then begin to run rough, then take off again. I’ve inspected/cleaned/replaced the spin on primary, water separator, secondary element, HP fuel pump suction element. Removed HP fuel pump, replaced screen/ insulator, inspected cleaned VST tank, overhauled. Checked for blockage in the return vent tubing, changed spark plugs, checked V-TEC solenoid oil screen. Everything is/was clean. I don’t have a test prop a test tank or the diagnostic tools.
I dropped it off at a Honda shop that ran diagnostics. They just hooked up the earmuffs. They say coils and injectors are good. However, they found some irregular values at the idle control valve (0 instead of 5.3) and spark advance seemed to be “a little off”. Tech said they’ll try a new oxygen sensor… and hope that straightens out the irregular readings.
Anyone have any experience with something like this? Any advice please? Thanks from the PNW🍺
 
20 hours a year since new- how big a fuel tank are you running? Could be an old fuel issue? Did you find anything dirt or water wise in your fuel water separator or the filters you changed?
 
Hi,

NSDON makes sense...usually does.

I have no expeeience with that model so my comments are "general".

Besides fuel quality as noted above, I would be interested in fuel pressure. Specifically what the pressure is when the problem is occuring. That's not as easy to test on an outboard as it is on a road test for a car so, it's a problem even for most small shops. But, someting a determined owner can do with the help of another person.

I kinda hope the O2 sensor fixes it but make dang sure, if they're selling you a new one, they give you your old one back in case it doesn't!

The idle air contrl valve has a screen filter that can get very dirty so you'll want that checked, cleaned or replaced. Item 19 in link below. Easy to do yourself. And I say that because, that way, you'll know for sure.


If that screen is packed with dirt, I recommend removing and cleaning the throttle body using great care in handling it and cleaning it. Use only "throttle body cleaner" and no scrubbing! Not even with a soft cloth!

Avoid the temptation of manipulating the Idle air valve by hand or opening the throttle blade wide. You can damage the IAC and if the throttle blade is allowwd to SNAP shut accidentally, damage can occur not only to throttle body but delicate fingers too!

Good luck.
 
Check the orings on the fuel water separator and low-pressure filter look for any flay spots or hardness, might seal enough to not leak when sitting but when suction applied air might be getting thru loosing. + if neither you need to connect fuel pressure gauge and run it til it repeats problem and see if pressure drops if it drops would indicate over heating or malfunctioning fuel pump
 
There are also other vacuum tests that can be done, one is to measure the vacuum the fuel pump is able to develop and the other is to measure any restriction in the fuel system between the tank and fuel pump/filter. Iboats has a section that explains how to do both using a fuel pressure/vacuum gauge. When I get a chance I’ll try to post a link to it.
 

HOW TO: Testing your boats fuel system.

Note, this was originally posted courtesy of Don S. Minor edits and pictures added by CaptJason A lot of you folks out there seem to be tearing into carbs quite a bit. Before you choose to open up a carb, you really need to look at what's feeding the carb first, and that is the boats fuel...
forums.iboats.com forums.iboats.com
take a look at this
 
Your on the right track of it being a fuel supply issue. Watching a fuel pressure gauge when it acts up would be helpful. Running it off a seperate portable fuel tank with its own dedicated fuel line directly to the engine could rule out a lot of upstream issues.

The o2 sensor and IAC don't affect high speed operation, doubt replacing those will help.
 
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