Honda bf10 loosing power underload

Hi guy's, have a 2008 Honda Bf10 fourstroke outboard. Starts first pull, runs fine on muffs but when i put in water and go for a drive, it will loose power at full throttle and go to a trawl speed for 20 seconds then speed up to full throttle for 60 seconds then back to a trawl speed for 20 second then speed up for 60 seconds and so on. Sometimes it will just stay a full speed and not loose power. It never stalls, just looses power when under load. It runs fine on muffs. I have cleaned carby, check for air leaks along fuel lines and fuel tank. Started to think maybe fuel pump or something else but what else could it be. Any help would be great.

If it is an instant chage in power level then look for spark issues as stated.-----Use a timing light to see if you can determine top or bottom cylinder.

Ditto to all the above. It could be as simple as a bad spark plug. Make sure you put in the NGK CR5EH-9. Do not use Denso's.

Even if a plug looks good, it could be arcing internally. You would lose spark in one cylinder but not the other.

If your oil level is too high, it can cause the bottom plug to get fouled. So, also check your oil level. Should be about 1/4 inch below the full mark.

Mike

hondadude said:

Ditto to all the above. It could be as simple as a bad spark plug. Make sure you put in the NGK CR5EH-9. Do not use Denso's.

Even if a plug looks good, it could be arcing internally. You would lose spark in one cylinder but not the other.

If your oil level is too high, it can cause the bottom plug to get fouled. So, also check your oil level. Should be about 1/4 inch below the full mark.

Mike

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I have ordered new spark plugs and i will see if that sorts out the problem, thanks guys and will let you know if that sorts out the problems.

Still running bad at top revs, runs nice until full throttle and then starts popping and running rough at full reves, any more ideas as i'm thinking maybe coil now.

Have you done any testing ??

You could very well be right about the coil breaking down. This symptom sounds like that COULD be happening. Although the coil and plug wires are sold as a "unit", I believe you can unscrew the cap ( I don't know YOUR specific engine) on the end of the wires at the coil towers and look at the ends of the wires and inside the towers. It's a good idea to make sure the caps are on tight at any rate. One thing I've noticed when I find a coil that is going south (only twice in 7 or 8 years) is that there will be what looks like rust staining on the ends of the wires and inside the towers where the electrical contact is made.

However, I wanted to tell you that we have seen a similar complaint on a small twin recently that ended up being a poor connection at the CDI connector. The guy found it by getting it to act up and then wiggling the connector and having the problem go away. I think he too, at first...cleaned the carb and replaced the jet set..... purchased a coil.....then a new CDI....and...when it still did the same thing, he found that he could actually make the problem happen by pushing on the connector in a certain direction. He ended up doing a bit of McGYVERING to make the connection there a solid one and reported back his success.

I'm hoping you too may be able to do some "wiggle" testing with the ignition wiring and find something going on that can be easily and cheaply resolved. Also, racerone's timing light test is a good one too. I use that a lot myself to identify no spark conditions although, I realize many guys just aren't set up to do that. If your engine is a pull start only, it not only requires that you own a timing light but you must also rig up a 12 volt battery to power it.

QUESTION: have you tried squeezing the primer bulb when the "breakup" is happening? If the problem stops when you do that...it's probably a fuel delivery issue and not an ignition problem at all.

Good luck and let us know what, if anything, you find.

Tried squeezing primer bulb while it happen, it was nice and hard and still played up. that was one of the first things i did. I first thought it might be the carb bowl running out of fuel and i had to wait for it to fill up to go full throttle again so i adjusted the float and still did it. I have removed fuel line from fuel pump and good flow of fuel is pump out of fuel pump but i don't know what pressure due to i don't have a tool to test it with. I will clean all electrical connection when i fit the new coil just in case it was what you described.

Well, it sounds as if you have eliminated fuel as the problem. But before spending the money on a new coil I would urge you to do the wiggle testing first. Also, make sure that the spark plug to coil hold down caps (if yours has them) are both tight.

One other area that COULD cause this sort of problem would be a valve adjustment or valve timing issue. Make sure that your valve clearance is properly set and that there is no undue slack in the timing belt. I have also seen broken valve springs cause high speed breakup like this on engines too. Just not on a Honda outboard YET. But popping off the valve cover to look at the springs and check the valve clearances is well worth the effort in the peace of mind it can bring should this problem persist.

There's no worse feeling than looking at a handful of expensive parts you just replaced only to have your outboard still giving you fits.

Good luck.