BF15A 15hp Honda Won't run at low RPMs

Thank you guys in advance for all your help.

Super Frustrated at my kicker

The motor will start and run at about 2500 rpm with the choke about 1/2 out. As soon as you try to close the choke it shuts off...like completely shuts off. I can sometimes catch it by pulling the choke back out quickly. The carb is clean...I've had it off about 4 times. The plugs are new. The fuel pump is pumping. I can't for the life of me figure out why the old girl wont stay running. When it is idling at 2500 with the choke 1/2 or 1/3 out it seems to run smooth just way too fast to shift it into gear.

Ideas would be appreciated. about ready to give up :-(

Thank you,
Rob in Seattle

The carb is still not clean or your idle mixture screw is not set correctly. It should be 2 3/4 turns out for most of the 15's. If your serial number is 1300001 or later, it should be 3 turns out.

If that does not fix it, then....Your idle passage is the problem.

I do not know what year your motor is, so I just picked one as an example. Part #11 (jet set) http://www.boats.net/parts/search/Honda/Outboard Engine/2001/BF15A1 SA/CARBURETOR/parts.html

picks up the fuel and takes it to the top of the carburetor. Therefore, it should be perfectly clean. The passage through it is very very small. They are typically hard to clean very well, but you could try with a very small wire and cleaner.

The o ring at the top of the tube (jet set) needs to be in good condition. And it needs to seal well. So, it would probably be worthwhile to get an o ring set #1. Put a little oil or lubricant on the o ring and the jet set should pop right into place.

Once that is clean, then you need to take some brakekleen with a straw on the can and stick it into the hole at the top of the carburetor, where the jet set would go.

Look into the end of the carburetor that is toward the intake manifold. At the top you will find a pin hole or two. If you open the butterfly, you should see a few more pin holes.

When you shoot the solvent through the straw into the jet set hole at the top of the carburetor, you should see a good spray out of all of those holes. If not, you need to backprobe and spray back through those little pinholes and keep working on it until there is a good spray out of them.

At the same time, you should see solvent coming out of a small hole at the front side of the carburetor. That is the idle air jet. You can spray back through that also, to be sure that everything is dislodged.

If you can remove the idle mixture screw, you should also shoot through that hole. Leave the screw in, at least some, for shooting fluid through the jet set hole and the air jet. It just allows more pressure at those small pin holes.

Finishing up....what is happening at idle....

The fuel goes up the jet set tube to the top of the carb and it combined with air, from the idle air jet. The idle mixture screw controls how much of a flow that will come out of the pin holes. At idle...with the butterfly closed.....the single pin hole feeds fuel to the intake. When you throttle up and open the butterfly, the other pin holes contribute more air/fuel mixture for the transition to midrange, where the main nozzle (big tube in the middle) kicks in adding more fuel with the air rushing through the venturi (carburetor opening).

I always recommend to replace the jet set if it is plugged to any extent. That is the only way to know for sure that it is clean. The inside of the tube is actually two sizes and there is no way to see if all the debris is removed from the corners where the two pieces meet.

If you purchase any new parts, be sure to look them up by your frame serial number to be sure that the parts are correct. There are some differences over the years.

Hope that helps.

Mike

One further point: The "Choke" in my BF20 Honda carb does not operate like a traditional choke, blocking outside air and using manifold vacuum to draw extra fuel through the regular jets. I assume the BF15 is the same.

Instead, it is an independent "fuel enrichment" circuit, opening an air valve and mixing that air with an independent fuel source, and leading that (richer) mixture to a point next to the manifold. The advantage is that (I suspect) it is less likely to flood the engine when the throttle is advanced. By opening the "choke," you are ~replacing~ the idle circuit at small throttle openings.

Also, if your motor has the idle mixture cover in place, it IS possible to gently excavate it without breaking the stem of the mixture needle off. When I replaced the idle mixture screw, I a) left the "nanny state" cover off and b) filled the break-off groove in the screw with hard solder to allow further maintenance in the future.

Hondadude, have you had any success with removing the welsh plug above the idle jet drillings? The plug isn't listed as a part, but it may be a standard size...

Never had to remove the welsh plug.

The 20D carburetor is totally different than rsamsel's 15A. The 15A has a physical choke plate that closes when the choke is pulled out.

The idle circuit functions pretty much the same.

So, rsamsel......here is looking to a clean idle passage.

Mike

Do EXACTLY as hondadude says and REPLACE that "JET-SET" tube as he suggests. That way, your outboard will run as it should at the end of the exercise and you won't be left guessing about what the problem is. Those jet sets have driven me crazy before and I don't mess around trying to clean them anymore. They just aren't that expensive to replace. This is also a true statement about putting it back together using all new gaskets.

Good luck!

Took me forever to get to this project.

Hondadude...first thing AMAZING reply. Probably the best reply I've ever had on any forum. Thank you.

Ok...here is my result so far. Went to pull it apart one more time! I know you are on to my problem as in my two previous cleanings i didn't remove that jet set. I did remove the nozzle main (#12) but didn't know enough to pull the jet set out. Should have gotten a book. Too used to my motorcycle carbs with a diaphragm and all connected to that jet set.

Well...problems right away. The plug (#8) is stripped and i ended up just drilling it out...total hack i know.

Here is my decision now. Ill need:
Plug (8)
Nozzel (12)
Jet set (11)

And a full rebuild kit.

Or a whole new carb. I am leaning toward a new carb. What is the trick to know which carb i need? The carb body says 068a hf15 if that helps.

I appreciate the help more than you know. Im trying to keep an old glasply out fishing but it's definitely a struggle sometimes when shops charge about 4x what i make an hour

Rob
Maple valley wa

Post your frame serial number. I am concerned about the numbers on the carburetor.

Usually...they are something like BF06FA with some variation. If it is, my part program says that the carburetor is no longer available.

Your serial number will let me check for sure.

Mike