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BF 25 cold start and idle issues

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Cade wallace1234

Member
I have a 2010s bf 25 I’m 15 years old and not a mechanic. It will run pretty good once I get it warm by using the accelerator pump. But it’s like a 5 minute process. I cleaned the carbs several times and I’ve cleaned the by starter and the by starter ports. It seems like the mixture needs to be adjusted however the only thing I see to adjust it is this spring loaded screw but it can only go back and fourth like half a turn each way. Anyone got any Ideas I’m really in a pickle here.Oh also it’s got spark on all 3 cylinders
 
Hi Cade,

You're pretty brave to tackle these carbs at 15. Kudos to you!

I hope you took lots of pictures to use for reference before you started tearing things down.

Since it idles and runs ok after you get it warmed up, I would not mess with that idle mixture screw with the plastic, break away, limiter cap just yet. It's likely not the problem.

This does sound like an SE circuit issue to me.

QUESTION: When you cleaned the #1 (top) carb, did you run a wire through the little "tunnel" in the bottom of the float chamber that feeds fuel to the SE supply well?

That little passage can get plugged up with "mud" because it's at the bottom of the float chamber. If it's plugged, little or no fuel will reach the enrichment well to help start the engine.

If that little tunnel is clean, then there may be a problem with the enrichment valve and you would need to test it. That valve can get stuck in the extended position and shut off the fuel for enrichment.

Sorry you're having troubles.
 
Thanks for the reply man, I believe I’ve cleaned every little passage way on the carb is there some kind of reference I could look at to see the exact passage you’re talking about?
Your going to have to bear with me because like I said I’m certainly not a mechanic.
Are you talking about the passage under the float and needle? Or something else. Also are these Honda carbs notorious for not working properly?
Anyways any kind of advice would be helpful because I’m dead in the water right now.
I’ve worked on a bunch of old outboards but this one is the problem child.
 
Well,
These Keihin brand carbs are notorious for not tolerating contaminated fuel and for being difficult to get clean after they get plugged with deposits.

Otherwise, they are as reliable as any other brand and, in the case of Honda outboards, VERY efficient as long as they get fed good, clean, fresh gasoline.

I will try to post a picture from the carburetor manual for you but you'll need to give me some time to get that done.

In the meantime, study the carb tube arrangement in the link below and make sure you put yours back EXACTLY the same.

Because, you mentioned an accelerator pump earlier but this set up doesn't have a dedicated accelerator pump. It uses a dashpot diaphragm along with a calibrated check valve (item 13 in the link) to provide a shot of fuel for rapid throttle opening and anti-stall when the throttle is quickly closed.

That system relies on those tubes and the check valve to be properly installed and oriented.


Also, make certain the fuel transfer tubing for the Service Enrichment (SE) system is correctly installed and there are no leaks. See items 41 & 42 in the link below:


I will get to taking and sending the picture of the SE well feed passage as soon as I can so please be patient.
 
Also I’ve read everywhere that the bystarter is supposed to get really hot after running for awhile. However mine is not. I’ve also checked the fuses and the ground and everything is wired properly. Is it possible I would need a new bystarter?
 
Here's the passage in the bottom of the float chamber bowl that can be plugged up with gunk. It can't always be cleared with carb spray if it's packed in there. It's best to run a stiff wire in there and move it back and forth to break up the mud THEN blast it with carb spray.

Sadly, if you don't remember making sure it's clear, then the only way to check requires removing the carb again. Which, as you know, means taking them all off.

I would remove and test the SE valve before doing that though.

If you do end up needing to disassemble again then you should use the opportunity to check and clean some things that most "first timers" typically miss on these.

Also, if you want to synchronize the carburetors, you WILL need to remove the idle mixture screw's. A real pain but it IS part of a thorough cleaning and tune.
Cade wallace1234 said:
Also I’ve read everywhere that the bystarter is supposed to get really hot after running for awhile. However mine is not. I’ve also checked the fuses and the ground and everything is wired properly. Is it possible I would need a new bystarter?
Click to expand...
Yes, the bystarter should get hot when the engine is running.

Here's how it works....
With the engine off, the bystarter is defaulted to "full rich" for helping the engine start. That means that the pintle valve rod is fully retracted by a spring and the enrichment passage in the carb is open.

After the engine starts, the bystarter coil under the flywheel starts producing about 12 volts.
As the engine runs and voltage is provided to the valve, it heats up after about 2 to 3 minutes and melts a wax pellet in the valve. The wax expands and pushes the valve pintle rod down....much the same way a car's cooling thermostat does.
When the rod has extended about 3/16", it closes the enrichment passage and leans out the air fuel mixture to keep the engine from stalling.

When the engine is stopped, the SE valve gets no voltage and the wax rapidly cools. The cooling wax contracts and the spring pulls the pintle rod up opening the enrichment passage so that gas can flow during the next start up.
 

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You should make sure of your starting procedure.... bulb pumped up to make sure carbs are full and closed throttle while cranking and for first couple minutes.
Enrichment needs closed throttle
 
siscoken said:
You should make sure of your starting procedure.... bulb pumped up to make sure carbs are full and closed throttle while cranking and for first couple minutes.
Enrichment needs closed throttle
Click to expand...
I will try that but I am a duck hunter and I don’t want to hear the starter crank for 5 minutes to start it up.
 
jgmo said:
Here's the passage in the bottom of the float chamber bowl that can be plugged up with gunk. It can't always be cleared with carb spray if it's packed in there. It's best to run a stiff wire in there and move it back and forth to break up the mud THEN blast it with carb spray.

Sadly, if you don't remember making sure it's clear, then the only way to check requires removing the carb again. Which, as you know, means taking them all off.

I would remove and test the SE valve before doing that though.

If you do end up needing to disassemble again then you should use the opportunity to check and clean some things that most "first timers" typically miss on these.

Also, if you want to synchronize the carburetors, you WILL need to remove the idle mixture screw's. A real pain but it IS part of a thorough cleaning and tune.

Yes, the bystarter should get hot when the engine is running.

Here's how it works....
With the engine off, the bystarter is defaulted to "full rich" for helping the engine start. That means that the pintle valve rod is fully retracted by a spring and the enrichment passage in the carb is open.

After the engine starts, the bystarter coil under the flywheel starts producing about 12 volts.
As the engine runs and voltage is provided to the valve, it heats up after about 2 to 3 minutes and melts a wax pellet in the valve. The wax expands and pushes the valve pintle rod down....much the same way a car's cooling thermostat does.
When the rod has extended about 3/16", it closes the enrichment passage and leans out the air fuel mixture to keep the engine from stalling.

When the engine is stopped, the SE valve gets no voltage and the wax rapidly cools. The cooling wax contracts and the spring pulls the pintle rod up opening the enrichment passage so that gas can flow during the next start up.
Click to expand...
I’m going to clean out that little hole and if that doesn’t work I’m gonna order a new bystarter. I really appreciate your help I will let you know what happens.
 
Cade wallace1234 said:
I will try that but I am a duck hunter and I don’t want to hear the starter crank for 5 minutes to start it up.
Click to expand...
Shouldn't have to crank for 5 min.... just closed throttle for start up.
Not the same as Honda with choke .... with choke you can crack thottle.
Enrichment type like yours will crank all day long if you open throttle.
My neighbor had the same issue as you and that is all that was wrong ....corrected procedure and never had another problem
Not saying this is your problem, just offering .... good luck with your Honda.... the bf25 is a great motor
 
siscoken said:
Shouldn't have to crank for 5 min.... just closed throttle for start up.
Not the same as Honda with choke .... with choke you can crack thottle.
Enrichment type like yours will crank all day long if you open throttle.
My neighbor had the same issue as you and that is all that was wrong ....corrected procedure and never had another problem
Not saying this is your problem, just offering .... good luck with your Honda.... the bf25 is a great motor
Click to expand...
Ok I gotcha but if I don’t give the throttle a few pumps it won’t even try to start. I have to use the throttle to squirt a little fuel in but after pumping I close the throttle all the way.
 
Cody,

If you take the carbs off to check/clean that passage, there are other things to check clean on all three carbs that you probably missed because you're new to this.

Such as:

main air and slow air jet passages whose passage entrances are on the front mount flange of each carb.

Did you backflush all of the delivery orifices at the top of rear of the carb throat? You can't see most of them with the throttle plate closed.

Did you inspect the slow air emulsion tube (jet set) with a magnifying glass? Those tubes are HARD to get clean and they will also crack up the side. Also, don't reinstall a jet-set tube without using a new oring. It's THAT critical to the operation of the carbs.



Don't buy a new SE valve until you test the one you have first. It's very simple to do. You say your's isn't getting hot but....is that because it's bad? OR...is that because it's not getting power when the engine is running?

Those SE valves very rarely fail.
I had a spare one in my parts bin for the carbs I repaired and never used it in 4 years.
 
Yea I cleaned the jet set out really well but I will triple check everything and make sure all the little holes are clean. I will go buy some new o rings because I didn’t replace those and they looked a little warn.
 
Cade wallace1234 said:
Yea I cleaned the jet set out really well but I will triple check everything and make sure all the little holes are clean. I will go buy some new o rings because I didn’t replace those and they looked a little warn.

Ok, good!
Yes! The oring seal for.those jet set tubes are very important. You should take great care putting the new orings on the tubes and then lightly lubricate them with Vaseline before inserting the tubes up into their holes so they don't pinch or roll going in. Way more "touchy" than most people think.

You also need to be careful about tightening the cap or "plug" at the base of the main jet that holds the emulsion tubes in place. Overtightening that plug is what causes the jet set to crack and split up the side. Again.....more "touchy" than you think.

I am happy to help you and I will take more pictures if you need them to understand what I'm talking about.
You just need to know that I'm in the middle of something very big at the moment and I won't always be able to get right back to you every time.
I will do all I can to help but, if you don't take my advice because you're in a rush, it's probably not going to work out well.

Also, you need to answer MY questions.

Don't buy any parts until you know everything you're going to need. Make a parts list instead so that you can order everything at once.

That brings me to gaskets.

You have carb experience so you should already know that carburetors work because of air flowing in the right places, at the right times and throttle settings.

While it IS possible to reuse gaskets if you find that you need to "go back in" to fix something you missed, the gaskets should be new, in good shape and you should handle them carefully. If you do an "oh crap" and booger one up you should be willing to replace it.
Reusing old or "repaired" gaskets is a recipe for failure.

Ok, FIRST QUESTION....
Do you know where the air vents are and how well did you clean them? (Not air jets...air jets are different and we'll cover them later)
Click to expand...
 
No.

The atmospheric vents are made into the top of the carb body. One left...one right.

They lead to tiny holes that "breathe" the inside of the carb. They're important because they let the outside air pressure (14.7 psi) push on the gas in the float chamber to make the fuel travel upward during operation.

I'll send you a couple of pictures when I can. It might be awhile though.
 
They were plugged up and I cleaned them out
jgmo said:
No.

The atmospheric vents are made into the top of the carb body. One left...one right.

They lead to tiny holes that "breathe" the inside of the carb. They're important because they let the outside air pressure (14.7 psi) push on the gas in the float chamber to make the fuel travel upward during operation.

I'll send you a couple of pictures when I can. It might be awhile though.
Click to expand...
ill look into that take your time I’m not in too big of a hurry
 
Well, I think you were right. The vent,s on your carbs may have hoses
attached.

The vent holes in the top of the chamber are at the tips of the arrows in the photo.

Make sure carb spray passes through both and out the vent nipples.
 

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I cleaned out that tunnel (fillled to the brim with crud) It took me a solid hour to get it all out. I used mig wire and had to fish it out. I’ll let you know Tomorrow if it starts eazy. I would tonight but I don’t wanna piss the neighbors off.
 
Ok, that was more than likely the starting problem rhen. Hopefully everything else you did was good enough. Although, I do hope you flush the atmosphere vents and replace the worn jet set orings.

I'f you find that it lacks top end performance or has a rough idle then there are other things that you could do now while it's apart instead of going back in again.

But, sounds like you're wanting to get you some ducks.

You do seem have the intake assembly and carbs on zippers anyway so, you're pretty quick for a "young-un" :~).

Good luck..
 
Yeah man thanks for the advice ill let yk how it goes in the morning I’m gonna hook the water up and see how see runs! Btw I’ll be praying for whatever you said was big in your life turns out well!!
 
Thanks for the good wishes and prayers Cody. I'll take all I can get! I need 'em!

One thing that bothers me though is the SE valve not getting hot. If it won't extend and shut off enrichment, then you'll probably have the opposite problem to what you have now.

IE: engine starts up easily but after a few minutes starts sputtering and stalls because it's too rich.

???

I guess we'll see.

Good luck.
 
Runs absolutely perfect it’s 31 degrees out side and I just touched the key and it started right up. Then the idle slowly went down to normal (so I guess my bystarter wasn’t bad).
Revs up good and doesn’t stall. I really appreciate all your help. I couldn’t thank you enough!!!
 
That's great news Cade!

It was my pleasure (and hobby) to help.

You're obviously a pretty good mechanic and would have figured it out eventually at any rate.

Apologies for calling you Cody....

In my defense, that happens to be my neighbor's name....
And.....
I'm old!

Hope you enjoy your Honda now. They are beautiful things...
...when we ain't workin' on 'em that is!🤪
 
jgmo said:
That's great news Cade!

It was my pleasure (and hobby) to help.

You're obviously a pretty good mechanic and would have figured it out eventually at any rate.

Apologies for calling you Cody....

In my defense, that happens to be my neighbor's name....
And.....
I'm old!

Hope you enjoy your Honda now. They are beautiful things...
...when we ain't workin' on 'em that is!🤪
Click to expand...
Ain’t that the truth
 
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