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2010 Honda BF225 starts immediately but dies as soon as the rpm’s fall from the initial start.

“What would the two have in common at the controls?”

Should be nothing, they get power separately, the throttle and shift cables are separate, they do share a key panel but other than the plastic panel the wiring should all be separate. I do have a Fell overboard device that interrupts the kill switch however it makes a bunch of noise when it shuts down the engines so I doubt that’s an issue (it’s wired correctly with the resistors to support twin outboards).

My other thought was to install a digital fuel pressure gauge in place of that relief screw. Is there a specific set of pressures I should see for the various stages of startup (priming, cranking, running) or is it always going to be 40ish psi?
 
Usually if they start with a little throttle it means the idle air control valves are clogged aswell as dirty throttle bodies, am item thats commonly overlooked in the marine environment. Remove and clean the throttle bodies and IAC filter screens
 
Going back over this thread, I didn't see where you checked/cleaned the IAC valve filter screens. Have you done that yet? Ian recommended that in his comments before and he's someone here that I would listen to on these big outboards.

There's also the possibility of the throttle bodies needing cleaning but, never having worked on one of these, I'm not the one to instruct you how to go about that other than to say "very carefully" should you decide to try. Only throttle body cleaner and proper technique should be used.

While outboards don't injest dirt anything like car engines do, they will still get an accumulation over time so you have to watch for that.

P.S.
Ha ha...I see Ian already beat me to it!
 
Again, I have no experience with this outboard but just want to say I have cleaned my share of automotive throttle bodies and it is most effective if the part is removed so that you can gain access to the back side of the blade. If you remove it to clean it, you will want to have a new TB gasket on hand.


In this case though, I believe that these are purely mechanical and you can open it with the throttle lever to gain access to both sides. That might be good enough. Not something that you would want to do with an electronic TB.

But, remember, use throttle body cleaner only and be aware that you will be spraying liquid into your intake and it could "pool up" inside there. Allow plenty of time for that excess cleaner to evaporate before attempting to start the engines to avoid the possibility of liquid "slugging" of the cylinders.

You will also want to be cautious about how you handle the idle air control valves. While some will tolerate being manipulated by hand, many will not and can be damaged that way. If you're not sure, best not to change it's position OR spray cleaner where it might enter the stepper motor housing.

Hope that works for you.

Good luck.
 
Iang6766 and jgmo, yall are awesome! I pulled off the IAC bodies, they both tested ok at 9.5 ohms but the screens were a bit black so I cleaned them off. Seemed like some oily film? Both engines just started right up. Thank so much, hopefully this rabbit hole of troubleshooting is at an end, and at least I have a brand new fuel system 😀
Will pull the throttle bodies off and fully clean next time I have the boat out of the water.
Cheers
AC
 
To make sure I understand what was happening, the IAC overrides the throttle body plate when it’s closed, since it was plugged up it caused the initial start to fail due to lack of air not fuel, that’s why when I cracked the throttles open a bit they started right up.
What would cause the build up, it’s odd to me they both started having the issue at the same time, one about 10 hours after the other.
 
There's a few things going on that cause that dirt to accumulate but mostly it's about time and emissions control.

Some of the crankcase gasses are collected and sent back to the intake to be burned in the combustion cycle to help keep vapor emissions down. That's where much/most of the "oily residue" came from. That residue will, of course, catch dirt particles over time and foul the TB and IAC.

As to your last point, if the pair of engines were mounted at the same time and have the same/similar amount of running hours on them then I would consider it odd if both of them DIDN'T have the same amount of contaminates in the intake and exhibit the same symptoms.

I was actually thrown off a bit when I was first reading your post. You were saying that one was having issues but the other one was running fine.

It all makes sense to me now though.
 
Would a lot of running at slower rpm make this issue happen/ be worse? Conversely, would a long run at high rpm clean it up?
 
NSDON,

That's a good question but I can't offer anything but opinion.

Since some of the "dirt" is likely made up of tiny bits of carbon flaked off from the combustion chamber and entered the crankcase via piston ring "blow-by", I think yes, running at engine settings that would contribute to less complete combustion might worsen the condition. How much? I don't know.

But I don't think "running hard" in order to knock the stuff off in the intake would be effective at all.

This sort of thing is going to happen over time at any rate and, probably, is more a result of thousands of cubic square feet of air flow bringing in atmospheric contamination than anything else. It may have much to do with where you run and what's floating in that "localized" air.

As an example, I see reports where thousands of pounds of sand blow across the Atlantic from Africa every year.

You buy your outboard to use the way you want to use it and, if trolling and tooling around slow in the harbor is your thing, then that's what you should do.

Although, a good, long run in a boat is likely a good thing for not only the engine but for the soul!

Having to do maintenance a bit earlier than the other guy might be a "penalty" many just won't be able to avoid.

Happy Memorial Day and Go Kyle Larson!
 
NSDON said:
Would a lot of running at slower rpm make this issue happen/ be worse? Conversely, would a long run at high rpm clean it up?
Click to expand...
No, it's a filter screen and a service item, should be cleaned at least every 400hrs. It's not on the Honda service shedule but should be done. I would imagine more contaminants are accumulted with higher rpm use.
 
I was thinking an engine operated in the high end of the rpm range is producing hotter cleaner exhaust gases and burning off residual combustion gases. Low rpm operation below the torque sweet spot would be lugging the engine, creating more dirty combustion gases.
 
Nope, at high rpm you get more blow back during valve overlap aswell as more oil mist from the closed crankcase ventilation giving you a mix of oil carbon build up, although very little. I usually include IAC clean in a 400 hr service
 
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