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Honda BF 25D cold start issues

T

Tony Outboard

Regular Contributor
Hi All, I’m after a few ideas before ripping further into a problem I have, any suggestions welcome.
The fuel tank, lines, pump, filter are all good, as are the plugs although it does appear to be running quite lean, I’ve removed and ultrasonically cleaned the carbs but still she doesn’t want to start from cold, turns freely and tries to start on crank but it takes a while to actually get it started.
Any ideas ?
Does anyone know the default setting for the fuel/air screws on the 25D please ?
TIA. Tony
 
Have you checked the operation of the SE thermo valve?
You can test it with 12vdc. Make sure the polarity is correct. Black and green is ground.

Throttle plate on top (number one) carb must remain completely closed during cranking for proper enrichment.

Check valve adjustment if you haven't already. Tight valves = hard start.

Good luck.
 
My short, curt answers are because the site kept rejecting my longer answers. No offense intended.
 
If the motor is running OK when warm, pretty sure those mixture adj. screws are fine where they are. As @JGMO mentioned, the cold start issue may have (probably does have!) something to do with the enrichening device (forget the scientific name for that) located on the top carb -OR- the fuel passage leading to it. The simple test I use to see if that device is working is to let the motor run for a few minutes. The device is based on an internal heating element, and if you touch it after the engine has been running for a few minutes, it's going to be (SHOULD be) HOT so be careful. If it's not hot, it likely not getting power, has a bad ground, or it's actually gone bad. THAT's when you get the VOM out.

FAR MORE OFTEN in my experience, is there's a chunk of crud in the fuel supply passageway that supplies the tiny reservoir that feeds this start circuit. What makes this occurrence even more likely is the fact it's located in the very bottom of the top carb's float bowl. To make matters worse, there's a jet located in this passage that's going to do it's level best to keep you from poking a wire through it. Ultrasonic cleaning is no assurance it's clear. Compressed air or a solid squirt of carb cleaner, both confirmed as going all the way though (from the end you squirt to the end where it comes out) is about the only way to make sure it's clear. -Al
 
Ah Ha, many thanks for the replies so far Guys, this beastie doesn’t have the start enrichment device fitted. I’m popping down for a look at her tomorrow, will take note of the existing fuel air mix settings and then reset to 2 1/4 prior to first start and see if that makes any difference, if it doesn’t I’ll re-set back to what they were and await my 5mm carb balancing adapter and have another go when I come back from our holiday. I’ll let you know how I get on, visually the plugs do like they are running lean which is why I wanted to check the fuel air mix first.
This is one of those engines which I have zero idea of the history on and the new owner has never seen it start and run properly, I tweaked the idle up slightly while trying to move the boat to its mooring post purchase as it was hunting and cutting out at idle then it was just a carb clean.
 
Last edited:
Tony Outboard said:
Ah Ha, many thanks for the replies so far Guys, this beastie doesn’t have the start enrichment device fitted. I’m popping down for a look at her tomorrow, will take note of the existing fuel air mix settings and then reset to 2 1/4 prior to first start and see if that makes any difference, if it doesn’t I’ll re-set back to what they were and await my 5mm carb balancing adapter and have another go when I come back from our holiday. I’ll let you know how I get on, visually the plugs do like they are running lean which is why I wanted to check the fuel air mix first.
mots also one of those engines which I have zero idea of the history on and the new owner has never seen it start and run properly, I tweaked the idle up slightly while trying to move the boat to its mooring post purchase as it was hunting and cutting out at idle then it was just a carb clean.
Click to expand...

So this is an older motor with manual chokes?

If so, have you verified they are they closing completely?
 
It has manual and the solenoid operated remote to control and yes they work just fine, cold start takes a good 5-8 minutes and the choke needs to be open with the throttle about 4/5ths open.
 
Tony Outboard said:
It has manual and the solenoid operated remote to control and yes they work just fine, cold start takes a good 5-8 minutes and the choke needs to be open with the throttle about 4/5ths open.
Click to expand...

That doesn't sound right at all. This is after pumping the primer bulb until hard?

You have pulled the air box to actually verify the choke platess are closing when you think they are??
 
Alan Hicks said:
That doesn't sound right at all. This is after pumping the primer bulb until hard?

You have pulled the air box to actually verify the choke platess are closing when you think they are??
Click to expand...
100% Chokes are working as they should. Plugs are beige, on crank I get the “chuff” of trying to start but doesn’t.
 
Tony Outboard said:
100% Chokes are working as they should. Plugs are beige, on crank I get the “chuff” of trying to start but doesn’t.
Click to expand...

That sure sounds like lean to me. With the choke plates closed, fuel should just be pouring in there when the motor is turning over. No idea why that's not happening.
 
Ok a little update, went down to the boat, fuel/air screw settings were as follows:-
1 - 2 3/4 out
2 - 2 1/4 out
3 - 3 out
Reset them all to 2 1/4 out and tried a crank with choke , no fire.
Reached down and pumped the accel/decel diaphragm four times, tried a start, bingo, fired up straight away.
Now I have had the owner advance and retard the throttle a few times previously before trying a cold start and that seemed to have no effect (I wasn't there so whether he did it or not, I don't know)
I'm thinking that either
a. It just needs the throttle to be advanced to WOT and then bought back to neutral a few times (with a 3 -4 second pause between to allow the diaphragm to reset) prior to a cold start or
b. The dashpot check valve is weak/blocked.
At least we have progress so when my balancing kit is in hand I can go back to balance the carbs knowing that first start won't be a nightmare :)
 
Tony Outboard said:
Ok a little update, went down to the boat, fuel/air screw settings were as follows:-
1 - 2 3/4 out
2 - 2 1/4 out
3 - 3 out
Reset them all to 2 1/4 out and tried a crank with choke , no fire.
Reached down and pumped the accel/decel diaphragm four times, tried a start, bingo, fired up straight away.
Now I have had the owner advance and retard the throttle a few times previously before trying a cold start and that seemed to have no effect (I wasn't there so whether he did it or not, I don't know)
I'm thinking that either
a. It just needs the throttle to be advanced to WOT and then bought back to neutral a few times (with a 3 -4 second pause between to allow the diaphragm to reset) prior to a cold start or
b. The dashpot check valve is weak/blocked.
At least we have progress so when my balancing kit is in hand I can go back to balance the carbs knowing that first start won't be a nightmare :)
Click to expand...

Properly adjusted, the dash pot should have no effect on the throttle setting. It's purpose is to prevent the throttle linkage from returning to the idle position too suddenly, preventing the engine from stalling once started.

However, having the throttle cracked/just barely open is very likely THE best way to get consistent starts in my experience.

The starting procedure I use on motors I don't know-
Choke until it coughs/tries to start.
Release/open choke.
Crack throttle and let it crank it for a few seconds (10-15?)
Repeat as necessary

Some will start and run wit the choke on, while others will not. They have to be choked then cranked with the throttle just cracked
 
Alan Hicks said:
Properly adjusted, the dash pot should have no effect on the throttle setting. It's purpose is to prevent the throttle linkage from returning to the idle position too suddenly, preventing the engine from stalling once started.

However, having the throttle cracked/just barely open is very likely THE best way to get consistent starts in my experience.

The starting procedure I use on motors I don't know-
Choke until it coughs/tries to start.
Release/open choke.
Crack throttle and let it crank it for a few seconds (10-15?)
Repeat as necessary

Some will start and run wit the choke on, while others will not. They have to be choked then cranked with the throttle just cracked
Click to expand...
Many thanks Alan, much appreciated Bud.
 
Alan Hicks said:
Properly adjusted, the dash pot should have no effect on the throttle setting. It's purpose is to prevent the throttle linkage from returning to the idle position too suddenly, preventing the engine from stalling once started.

However, having the throttle cracked/just barely open is very likely THE best way to get consistent starts in my experience.

The starting procedure I use on motors I don't know-
Choke until it coughs/tries to start.
Release/open choke.
Crack throttle and let it crank it for a few seconds (10-15?)
Repeat as necessary

Some will start and run wit the choke on, while others will not. They have to be choked then cranked with the throttle just cracked
Click to expand...

Its a terminology thing, the dashopt and the diaphragm assembly I'm referring to are one and the same, just had a look through the carburetion manual and on the engine I'm working on it tells me that the dashpot/diaphragm gives me a squidge of fuel into the carb so although it will have no effect on the throttle, it will assist in the start which is possibly why I had the easy start this morning. Time for a little more nerdy reading for me.

Operation
• During Acceleration
When the throttle is opened quickly from a constant speed, the diaphragm moves to the full stroke
position. The carburetor main well is pressurized instantaneously and the fuel in the main well is
discharged through the main emulsion tube by the diaphragm pressure.
When the throttle is opened slowly, the pressurized air is bled through an air restriction jet, so fuel is not
discharged excessively.
 
Problem solved, the 3 small hoses which run from the diaphragm/dash pot to the carbs were a little worn at the ends, replaced then and added a ty wrap at each end to assist the sealing and it now fires up lovely. Thanks for you inputs Guys.
 
Glad you got it sorted out Tony
Thanks for the update and explanation
I still can't find a reference to a "D" model with a conventional choke. Do you happen to have a date of manufacture for that outboard?
 
jgmo said:
Glad you got it sorted out Tony
Thanks for the update and explanation
I still can't find a reference to a "D" model with a conventional choke. Do you happen to have a date of manufacture for that outboard?
Click to expand...
My bad it’s not a D model it’s an A but I can’t edit the title
of the thread.
 
Alan Hicks said:
If the motor is running OK when warm, pretty sure those mixture adj. screws are fine where they are. As @JGMO mentioned, the cold start issue may have (probably does have!) something to do with the enrichening device (forget the scientific name for that) located on the top carb -OR- the fuel passage leading to it. The simple test I use to see if that device is working is to let the motor run for a few minutes. The device is based on an internal heating element, and if you touch it after the engine has been running for a few minutes, it's going to be (SHOULD be) HOT so be careful. If it's not hot, it likely not getting power, has a bad ground, or it's actually gone bad. THAT's when you get the VOM out.

FAR MORE OFTEN in my experience, is there's a chunk of crud in the fuel supply passageway that supplies the tiny reservoir that feeds this start circuit. What makes this occurrence even more likely is the fact it's located in the very bottom of the top carb's float bowl. To make matters worse, there's a jet located in this passage that's going to do it's level best to keep you from poking a wire through it. Ultrasonic cleaning is no assurance it's clear. Compressed air or a solid squirt of carb cleaner, both confirmed as going all the way though (from the end you squirt to the end where it comes out) is about the only way to make sure it's clear. -Al
Click to expand...
I wish I had this info after 3 attempts to. Lean the carbs in my Honda bf
After cleaning that upper bowl and the small jet in the bowl it finally runs like it should
So many rabbits I chased
Slow jet
Sync carbs
New fuel lines
Spark plugs
Bystarter
This will be hard to keep from getting clogged with no availability of no ethanol fuel in Canada
 
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