Honda BF90a carb/throttle problem.

[JudgeSmails]

Just repowered with a 1997 BF90a I recently purchased. Before purchase did the usual compression check, inspected quality of the oil and lower unit grease. Ran in a tub and sounded good. Yesterday was the maiden voyage after putting it on my boat. Ran it gingerly for about a half hour and it seemed fine and sounded good. Did some WOT testing and all sounded good. Stopped the motor and drifted for about 20 minutes to have some lunch. I started it up and it stalled when I threw it in gear for a hole shot test. Started right back up and I did a more gradual acceleration which seemed fine. Ran around for a little while and everthing seemed normal until I tried to slow down for a cruiser wake and the throttle stayed stuck open. I killed the ignition and avoided swampage, but so much for feeling good about the new motor.

I took the linkage cable off thinking it slipped adjustment or something, but even with the cable off, the carb throttle would not snap back to idle. Nothing external seemed to be causing a blockage. I hooked the linkage back up and hoped for the best by starting it back up and immediatly throwing it in gear to get myself back to shore. Once I was within trolling motor range I put it back in neutral and this time the engine was able to rev down to idle. However, idle seemed a bit rough compared to the beginning of the day, and had a much more pronounced 'engine shake'. There is a pretty long no wake zone back to the dock, and after about 10 minutes of rough low rpm trolling there was a distinct misfire sound in quick sucession then the idle seemed to sound a little more normal. I landed with no trouble.

The air silencer cover over the carb intakes has a crack at the top that the previous owner tried to apoxy. There is a dime sized chip missing, but that is not new. I assumed it was simply missing and a cosmetic issue but did not pose a problem. I hadn't thought of it, but I suppose it could have been floating around on the inside of the air silencer housing. Is there any air filter or anything on the inside that would prevent something like that from getting sucked into the carbs? Any other reason why the throttle at the carb would stay stuck open like that? I've always had an older two stroke in the past and done carb rebuilds, but I'm reading that it's a totally different animal with the Honda 4 strokes. Should I do another (nearer shore) sea trial or is it straight to the mechanic for me? Any advice or cyber diag is appreciated.

 

[hondon]

Re: Honda BF90a carb/throttle problem.

As with most outboards, there is no filter in that airbox.That airbox has one screw that is inaccessble and is frequently broken off by people that do'nt know what they are doing.The only way to redo those carbs is to remove the manifold complete.

 

[JudgeSmails]

Re: Honda BF90a carb/throttle problem.

Thanks Hondon. I see that bolt you are talking about. It sure looks tempting.

Update: I reinspected the crack at the top of the airbox last night and the epoxy fix the previous owner had done failed spectacularly and I didn't notice it on the water. There is a huge 1x3inch chunk that fell off and is floating around at the bottom of the airbox. I'm going to guess that when the throttle stuck wide open that the chunk of plastic was keeping the bottom carb butterfly open and after getting back underway it vibrated loose again. That one will be easy to fish out but it begs the question... what smaller pieces are still in there? I think I'm looking at a carb disassemble to put my mind at ease.

But, after getting a better look at the inside of the airbox I couldn't help but notice that it would be really easy to drill 4 small holes in the front which would allow access to squirt some carb cleaner in while running. The holes can be plugged up with some screws when not needed. Has anyone tried this, and is carb cleaning spray advised on these honda 4 stroke carbs to clear out the jets every once in a while? I'm still trying to figure out what 2 stroke habits I need to adjust with these newer 4 strokes. Thanks for the advise.

 

[iowafish]

Re: Honda BF90a carb/throttle problem.

I'm running the same motor as you and love it. The 75/90 Honda carbed motor is a fine power plant but carbs can be a bit troublesome. The Honda carbs have several very, very small fuel ports and can clog with junk. Supplying the motor with clean fresh fuel prevents this. I'm installing a remote fuel water separator for good measure. Honda P/N 06177-ZW1-801AH is made by Racor and is a quality piece. Don't shoot carb cleaner through the carbs airway. You really won't clean any fuel passageways and you risk damaging your combustion chambers. If fixing that air box doesn?t solve your problem, I'd recommend taking the motor to a competent service tech and having your carbs professionally cleaned. Replace that air box first because that?s probably your problem anyway. You can often find these on eBay. Use Seafoam in your gasoline to keep the fuel from leaving residue and you will be fine for years to come. A little trick that my mechanic taught me is to pump up your primer bulb every few weeks or so when the boat isn?t in use. This keeps the fuel bowls full and voids oxygen thus preventing oxidation and keeps the gaskets from drying out. Happy motoring.

 

[JudgeSmails]

Re: Honda BF90a carb/throttle problem.

Thanks iowafish. I have the fuel water separator, and seafoam is already part of my SOP. Good to know that the motor will be a solid workhorse once I get the carb situation under control.