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Honda BF15A surging

C

captal

Contributing Member
Howdy folks! Have been a user of the inboard engine forums for many years but now I have to come the outboard gurus for some help. Just bought a used 1999 Honda BF15A four stroke. Low hours and looks great. Got it home changed the oil, lower unit oil, fuel filter, and a fresh tank of gas with a little Seafoam in it. Tested it out and it did fine on the hose. Put it on my 14' john boat and took off. First day ran great except fo the idle. Wouldn't idle down low without shutting off. Not a big issue with a motor that had been sitting. Used it all day and except for the idle issue ran flawless. Got home and took apart the carb, looked a little gummy, so soaked in carb cleaner, rinsed and put back on the motor. Test and the idle seemed a lot better. Back on the water today and the idle was right on. Idled down low and shifted smooth. Ran about 45 minutes and sat and did some fishing. Started heading back home and noticed an intermittent miss at high end. Just a "burp" now and then. The it started to get worse. Slowed down to 2/3 speed and it did good for while then started missing there too. About a half mile from the dock it would rev up then back to normal speed. Anything over half speed it would briefly surge then back to normal. Could feel the boat surge also. Got it home and started checking. Thought the lower unit might be going. Put shifter in gear and tried to turn the prop and it was firm. Couldn't feel any teeth grinding or slipping. And from most of my experience a lower usually lets go all togethe anyways. Checked plugs and they look OK. Gonna' replace them anyway. All wiring and connections look good. Any ideas out there and anything else to check? I have been wrenching on 2 strokes all my life but this is the first 4 stroke. Sure could use a little help!!!! BIG Al
 
One thing to do is to run with a timing light.-----This may help in determining whether it is an ignition fault or something else.-------Those carburetors have very tiny passage ways and jets.------Sometimes it takes folks 2 or even 3 tries to get these carburetors clean !
 
Thanks for the input racerone! I would like to think it's some type of ignition problem because the surge and the "burps" are so fast and deliberate. Usually a fuel problem last a few seconds. But since I had no problem till I cleaned the carb I'm sort of tilting that way. How would I tell using a timing light while running? The misses are instantaneous and the surge only lasts a second or so. I'm kind of a diagnosis nut versus a parts changer. But I am going to buy a carb kit and put it in anyway. I just cleaned it before. Any other ideas are welcomed to!!!! Thanks!!
 
Thanks Mike. I took the carb off again and am doing another detailed cleaning today. I didn't take the jet set out last time but I did today. The carb says KEI HIN as the manufacturer, part # 06FA MJ22. Not sure if it is a Honda carb or aftermarket. The idle mixture screw #5 is set in an indexed hole that only lets the screw move about an 1/8 of a turn at most. It has a screw slot but it is L shaped so it can't turn but so far in the hole. Don't think that is a problem though since the motor ran great for almost an hour before the erratic behavior started. I am running the NGK DR6HS plugs though. I'll let you know what happens in the morning. Thanks for the great input and exploded parts sheet!!
 
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