Hi all & BF15 fun

Hi to you all. I bought my first powered boat a few weeks ago after years of kayaking, a small inland cabin cruiser with a BF15A on the back. the engine ran ok but very smoky. Seems the previous owner had been fiddling about with it with no mechanical knowledge whatsoever!

First I found the engine oil had been filled to halfway up the dipstick. It was clean-ish and I had no fresh oil to hand so I drained it off to the correct level. That cut the smoking down but on the next journey out the 15hp twin turned into a 7.5 single. The plugs came out black and oily/sooty. Maybe just the excess engine oil fouling the plugs I thought, and replaced the plugs. Ok for a few hours running then back onto one cylinder (always the lower one). I removed the carb for a check-up and found what I believe was the pilot mixture screw on the right hand side of the carb. This was around 5 turns out! I presume (years of biker experience talking here) this is usually between 1 and 2 turns out and I reset it at 1 1/2 turns. I had to reset the idle speed when refitting and I've yet to check the colour of the plugs now but it was faultless for the 5hr trip back. Well... almost. My oil pressure light goes out when the engine is idling, comes on fine as soon as revs rise. This does not happen when cold, just when the engine has reached full temp.

Ok so 2 questions.

1. Does anyone know the factory setting for the pilot screw?

2. Is the oil light normal? Have I just turned the idle down too low, I set it to 'as low as it's happy and not stalling when put into gear'. It does seem a high idle to get the oil light flickering and it's constantly lit when cruising. I will give it an oil change next time I go down, what grade should I use?

Factory setting is 1 5/8 turns out. So you are very close.

idle speed should be 1100 plus/minus 50 in idle.

Oil should be 10w30.

It is possible that your oil is pretty fuel diluted due to the wrong adjustments..

Oil light should be on all the time. An oil change should help that.

Mike

Thanks Mike just the job. The fuel in the oil sounds possible, I thought the oil looked a bit thin though I run an old Rover v8 on 20/50, it's been a while since I've seen any 10/30. It would drop the oil pressure though. Thanks, I never thought of that

A couple of other things to check with this motor. Make sure that it is heating up to about 130 degrees. If it runs cold, that can cause fuel in oil.

Also, if you run this at an idle a lot, you should put in one step hotter spark plug (Normally they take DR6HS....one step hotter is DR5HS)

If you run it mostly at moderate to high speeds, stay with the DR6HS.

If you do not have an owner's manual for it, you can download one for free from the Honda website... http://marine.honda.com/Owners/Manuals/models/BF15

Choose by your serial number.

Mike

Changed the oil today and oil pressure back to normal, thanks again Mike. It gets run at all speeds, idling mainly at locks so I'll stick with the 6's.
Cheers
Ant

Captain Blues,

You could have any one or more of several things going on.

First, I am assuming this is a kicker used only for slow speed operation of a fairly good size boat (18 - 22ft or so). If my assumptions are wrong, let me know, because what I am about to saw may not apply.



1. If you have the carburator off and cleaned in out, be sure the idle passages are clear and the float is parallel with the base of the carburator when held upside down. There is a measurement of 13mm -15mm, but parallel usually works. It sounds like it is possible that you are running a little rich...but wait there is more...

2. You are very close on the idle mixture screw...the base turns are 1 5/8 turns out. If it runs good at 1 1/2, leave it there. It should be set for maximum idle, when in gear.

3. You need to be sure the engine is getting to operating temperature. The engine at the thermostat should measure about 170 to 180 degrees F. ( I need to double check this temperature...it might be closer to 130 F). I will check an actual thermostat tomorrow if I can remember. If it is a lot colder, the thermostat could be stuck open. If the motor runs too cold, the engine will not combust properly. End result is fouled plugs and fuel dilution in the oil. (Sound familiar?)

4. If you have a large boat and trolling, you should have a high thrust prop so you can keep the rpms up and not over strain the motor. We generally use a 10 x 7 four blade that Honda sells. It is the same one that we use for pontoon boats when small motors are on them. The Honda web site says this is for an 8D - 20D, but it will work nicely on your model 15.

5. 1. Check the compression to be sure that cylinders are ok. You sound pretty knowledgable about motors....so it would be good to check the valve clearances also. If the intake valve is too tight or the exhaust valve is too loose for that cylinder, it could cause fouling. I recommend getting a repair manual to step you through it. If compression differs between the two cylinders, that could be another sign of valve clearances out of adjustment.

6. Again, if you are always trolling, use a one step hotter plug...DR5HS. This plug burns a little hotter but will be too hot if running at high speeds.

7. Lastly, make sure your engine is perpendicular to the horizon. Not tilted in at the bottom. When the motor is tilted way in, the oil seems to find its way into the cylinders, causing fouled plugs. This would not be the cause of your oil dilution, but could add to your issues.

If all that does not work, then you may have a timing issue. I had a similar situation on an older 8 HP and it turned out to be a faulty centrigal arrangement under the cam pulley. It can not remember if the 15HP has such a way to vary timing. Normally, doing the above solves the problem or leads me into a direction to determine what is actually the problem.

That should give you something to chew on...

Mike