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Honda BF90a Limp Mode and exhaust not coming from prop etc

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Letalis

New member
Greetings! I've been lurking for a while reading up on all I can to try to get a new to me 2003 Honda BF90a going for the season. Have learned a lot here and using the information found, have been narrowing things down, testing, cleaning and replacing some stuff until I hit upon the possible issue(s) and wanted to see if I'm on the right track. Boat (engine) is heading into a local shop with Honda technicians but I wanna do all I can before then! The engine initially had a CLEAN dipstick with what looked like brand new oil and fired up prior to purchase but had a misfire in cylinder 4, showed 509 hours and well, the Honda name sold me. It now starts n runs awesome after replacing plugs n coils but... Did an oil change and it was chocolate milk!? and very dark but no silvery metal bits at all. Changed oil n filter... Solid pee stream from the engine and inspected/replaced the thermostat that was stuck wide open. A bit of build up in that housing can be seen but not bad. Compression tested (warmed up and with throttle as far open as I can in neutral cuz it won't turn over in gear/wide open, tested at a 195-200 psi across all 4) and running it on muffs, idles and the allowed bit of throttle up (not in gear) sounds great. Went to local lake for about a half hour to take her for a spin and in neutral with engine cover off, I can manually bring up RPM's to the amount allowed, the engine sounds great... In gear as I throttle up it hits a spot, lower rpm than when I tried in neutral, that makes it sputter and run rough almost dying. Max speed according to fish finder (Tach not working/fixing tomorrow) it was 7mph. Temp light was off and oil light on and green. Oil light turns off when engine alarm sounds then turns back on but did not die or shut down. Limp mode? Limped back and headed home for more work. Oil still looks great on the stick but I took a 1oz sample from the drain plug. Still transparent as in no water but very black from possible exhaust leak? Bought a 'tub' to put the entire lower section into and while in neutral or lowest RPMs in drive, exhaust isn't consistently coming from the prop area but rather from another seam in the case a couple inches up, not far from water inlet. Exhaust DOES come from prop when in gear, higher rpm's on the lake...

Do I have an exhaust leak into the oil somehow which in turn throws it into limp mode and maybe some moisture as well? I've read that the exhaust goes through the oil pan and there are lower seals that need to likely be replaced. Oh and oil pump/sensor may need replacing?

Thanks in advance.
 
Hi,
There are some guys here that will be of more help to you than me since I have no experience with this outboard. Be patient and you will likely hear from them all eventually.

I just want to warn you about being really careful about dealing with that repair shop.

There are so many fly by nite "money vampires" in the outboard "repair" business....many of which have a "Honda Dealer" shingle hanging out front!

Yes, Honda makes great outboards and yes, there are some very good Honda dealers and techs out there but I'm not so sure they are in the majority.

Do ALL THAT YOU POSSIBLY CAN to vette ANY shop that you take it to and get IN WRITING an agreement that states you will be consulted prior to any work being done along with a good faith estimate.

It sounds to me that you probably have the sweet makings of a used outboard there (200 compression!) so it would be a crime if some hack shop ruined it or turned it into a major money sucking event for you.

Sorry to be the "dark cloud" but that's the world we're in and I know of which I speak.

Best of luck.
 
UPDATE

Got tach installed and I was a little backwards there and a bit low. Idle max is 2200 rpm in neutral and in gear max is 3k before bogging down and trying to die. Going to check through fuel lines/filters etc next. Alarm and light for oil only happens when it sputters out when trying to push for more throttle than 3k rpms. Still no water in oil.
 
From where I'm sitting, it sounds like you're past due for a serious carb cleaning. That's something that can be done on a DIY basis, but it's NOT something you're going to get right if you are in any kind of hurry. There are some really tiny jets in play, and at least 2 o-rings.

The carbs are removed as a cluster by removing the intake manifold and the air intake muffler as a whole assembly.
 
Well, the stuck open Tstat was likely the reason for the "chocolate milk" oil.

As far as cleaning the carbs goes, I will warn you again about the total crapshoot it is to get quality work done. If you are at all inclined to try it, I urge you to go for it. As has been said, it's not super easy or quick but it is achievable if you take your time. I would also suggest that you first get a copy of the Honda Marine Carburetion Manual. $44 + tax and shipping

It's listed under "support material".

Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com publications.powerequipment.honda.com

Good luck
 
Thanks!! I'll get all manuals for the engine/carbs. I know how to rebuild carbs so this shouldn't be too bad. :unsure: Anyone got a link for the rebuild kit? Gonna need a new gasket for mounting the carbs too (y)
 

Honda Marine - Parts Look Up - Official Site

The official parts look up site for Honda Marine. Search for parts for your Honda outboard. Browse a complete online parts catalog for Honda Marine, create a wish list, and even email it to your local Honda Marine dealer.
peparts.honda.com peparts.honda.com

I don’t think Honda offers rebuild kits, order what you need. If you order from boats.net verify their part numbers with Honda’s part numbers. I don’t know why the “link” I provided to Honda’s parts page isn’t a link, copy and paste should
 
There isn't a "kit" for these carbs...no check balls, power valves or accelerator pumps. Well, a few have accelerator pumps but not yours.

Anyway, these carbs are all about tiny feed and hidden cast in vent jets. Getting them clean in a reliable manner is the "rebuild" so to speak. That's why I recommend the carb manual.

You'll likely be reusing most of the components except where you find damage or distortion.

You might only need to buy the 8 mounting gaskets and a "gasket set" that contains the critical orings. Items 22 and 2 in the link below


Honda Outboard 90HP OEM Parts Diagram for CARBURETOR | Boats.net

Buy OEM Parts for Honda Outboard 90HP CARBURETOR Diagram
www.boats.net www.boats.net

The exception to reusing parts is sometimes the low speed emulsion jet tube or "jet-set" as Honda calls it. Those can be a real pain to get deposits out of and, occasionally, they will split lengthwise. Item 18.

Sounds like you are confident in your abilities so that's what you mostly need. Just take plenty of photos during tear down. When finished, you will have learned MUCHO about your outboard and will likely have done a much BETTER job than any shop would.

Good luck
 
www.boats.net parts ARE genuine Honda parts and their inventory is the total of what Honda still supports for aging outboards along with lower prices.
If it says "unavailable" at boats.net then you won't find it at Honda either.
 
Agree with all of the above!! That gasket kit, with the tiny included o-rings are the important parts that can't be reused.

The #1 issue with getting these carbs to idle right is the tiny jet buried in the bore at the bottom of the tube marked #18. If you have your glasses on you HAVE to be able to see through the length of that tube to know it's clean. The jet is so tiny it's easy to trash trying to force too big a piece of wire though it. I use 1 strand of one of those small stainless wire cleaning brushes. Grab on with a pair of vice grips and give it a tug and you'll have yourself a tool that's just right for cleaning this tiny jet.

The other issue is the tamper proof screw on the end of the idle mixture adjusting screw. If you try to remove it without getting it hot enough to melt the epoxy that's holding it in place, you're going to break the head of the screw off. No maybee's....

I use a heavy soldering gun - and a lot of patience. You HAVE to pull straight up with a pair of needle nose pliers. If you try to pry or pull on it sideways, it's going to break, guaranteed. Yes, you bet. I've broken dozens of these. So here's something to think about. Have these tamper proofs all removed prior to ordering your kits. That way you'll how many of the adjusting screws you're going to need and you can order them with the kits, saving a few bucks on freight/handling fees. And don't even try to remove them unless you have the carbs off, on the bench.....

The screws with the broken off heads can be removed by carefully using a pick around the outside of the remaining screw head to turn them. I use a sharp #11 to do this - and a lot of patience - which is another reason for being super careful when removing those darn caps. When they're hot enough, it takes very little to remove them....

Oh, the reason you NEED to get that idle adjusting screw out? That o-ring located just behind the screw head. If it's leaking, the engine will struggle to pull enough vacuum to get fuel up to the idle jets located in the top of the carb. Those jets by the way, are your issue. They aren't getting the fuel they need. The biggest reasons for that include the plugged jet previously discussed, the o-ring at the top of that same tube, and the o-ring on the idle adjustment screw..... Best of luck!
 
WOW a lot to check upon but I'll be thorough and patient. Will have em on the bench Monday for tear down and begin cleaning. THANKS guys for all the potent info here. I have a friend that's a fuel systems professional with over 50 years experience in carbs including marine that's setting up my bench and helping me. I'll be sure to take pics and do a quality update for reference to share/give back to this community. Thanks again!
 
Where do I start? This poor BF90 had some issues but the low hours and high compression had me sure it was a safe bet. With some love, lots of swearing, lots of learning and such I'm happy to say she's a runner! Our new to us boat is good to go for the season. Special thanks to @Alan Hicks for the wisdom. The carb rebuilds went great and todays run on the local lake was a massive success. When we launched (of course there were a couple of us for this run) and tied off at the dock I left to hit the can and walking back I didn't think it was even started yet till I was 10 feet away. SUPER quiet idle and after a few low RPM laps, zero issues/smooth throttling up to 5500 RPM. I think the limiter is 6500 but didn't want to work the thing rough first time out. HEY! Couldn't be happier! Thanks again, everyone. Cheers and happy boating!
 

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