Logo
FULL SITE MENU

Honda BF40A 2007 bottom cylinder not fireing

B

Buster88

New member
Hi, I have been looking through this forum and it has helped alot. Thx.

I have a Honda bf40A from 2007 it only runs on 2/3 cylinders, i have cleaned the carbs but with no luck, if I spray som carb cleaner The third cylinder fires right up, so I am fairly certain I have a fuel issue, the slow jet is clean, and open. The o-Ring on the slow jet is a bit wir now, Could this little o-Ring aus my problem? Even if I give it more throttle so it should go over on Main jet it wont fire.

IT all started when Testing if it ran good for the season, it only ran on 1 cylinder 2 and 3 were dead. Remowe all carbs and cleaned after that it ran on 2/3 but still not fiering on 3 bortom cylinder. I dubble checked again that the slow jet Was open and not clogged and also the small holes inside avefything is open, but see3m it still gets no fuel. Hope someone has some sort on idea on this.
 
I don’t know anything about this motor but have worked on a lot of carburetors over the years. If there’s a drain on the bowl and if It has a bowl see if the needle is allowing fuel in the bowl. Also check to see if there’s a filter inside of the fuel line fitting where the fuel line attaches to the carb. The older 4 stroke carbed Yamahas have these and can cause a lot of headache if you don’t know they are there.
 
Lmoore87 said:
I don’t know anything about this motor but have worked on a lot of carburetors over the years. If there’s a drain on the bowl and if It has a bowl see if the needle is allowing fuel in the bowl. Also check to see if there’s a filter inside of the fuel line fitting where the fuel line attaches to the carb. The older 4 stroke carbed Yamahas have these and can cause a lot of headache if you don’t know they are there.
Click to expand...
There is fuel in the bowl, and its not going in overflow so that seems to work as it should. No Filters
 
Cylinder have good compression? I know you said it runs when sprayed in the carb but it will have to pull enough vacuum through the throat of the carb to pull fuel through the jets
 
Well, that little oring on top of the slow jet is very important . If your's is in questionable shape then, yes, replace it.

BUT...is that what's causing your problem??....
...I don't know.
Here's what I would do:

Replace the oring for carb 3 slow jet tube.

Make dang sure that the fuel orifice in the tube is completely clear. That orifice is in the bottom of the tube and sits below the fuel so it gets easily clogged and is
1. Very hard to see and
2. Is very hard to get cleaned once it's plugged.
So, use a magnifying glass and a flashlight when checking it.
Those tubes crack vertically so inspect for that carefully.
If there's ANY doubt about the tube, just replace the stupid thing.

With the tube removed, spray into the slow speed circuit toward the rear of the carb and observe the idle orifice at the top of the carb throat for good flow.
Actually, I would also fully prop open the throttle plate and place the tip of the cleaner straw directly over the idle orifice and give it a couple of good blasts. Cleaner should pour out of the slow speed circuit.

I would do the same for every orifice at the top of the carb throat.

Go to the front mount flange and locate the slow air jet tube (inner) and main air jet tube (outer) and blast them both thoroughly watching for fluid to exit the orifices at the top of the carb throat.
If you block the slow speed hole where the tube plugs in it helps to increase flow and scrubbing power.

Ensure that the atmospheric vents are clear. Locate their two holes at the top of the float chamber in the main body and blast them from the inside. Cleaning them from the outside sometimes forces crap back inside them.

If you didn't remove the idle mixture adjustment screw and clear the passage before, you have to decide if you want to do that now or re-install the carbs and try running again. But....if it still doesn't idle or runs like crap, you'll probably be taking them back off and doing that next.
Either way, it's a P.I.T.A.

If you want the Bible on getting these little "jewels" clean and dialed in it's here under Support Materials.


Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com publications.powerequipment.honda.com

Good luck.
 
I just saw Lmoore's suggestion about compression and I think he makes a good point. Also. you might also want to compare the spark for #3 to one of the other cylinders because carb spray is a bit more volatile than gasoline and weak spark could be an issue here too.

Both easier things to check before pulling the carbs again.

Good luck.
 
Lmoore87 said:
Cylinder have good compression? I know you said it runs when sprayed in the carb but it will have to pull enough vacuum through the throat of the carb to pull fuel through the jets
Click to expand...
I do not have the Tool to check compression, but I removed 1 screw on the on take manifold for cyl 3, and it has a good suction in The intake.
 
jgmo said:
Well, that little oring on top of the slow jet is very important . If your's is in questionable shape then, yes, replace it.

BUT...is that what's causing your problem??....
...I don't know.
Here's what I would do:

Replace the oring for carb 3 slow jet tube.

Make dang sure that the fuel orifice in the tube is completely clear. That orifice is in the bottom of the tube and sits below the fuel so it gets easily clogged and is
1. Very hard to see and
2. Is very hard to get cleaned once it's plugged.
So, use a magnifying glass and a flashlight when checking it.
Those tubes crack vertically so inspect for that carefully.
If there's ANY doubt about the tube, just replace the stupid thing.

With the tube removed, spray into the slow speed circuit toward the rear of the carb and observe the idle orifice at the top of the carb throat for good flow.
Actually, I would also fully prop open the throttle plate and place the tip of the cleaner straw directly over the idle orifice and give it a couple of good blasts. Cleaner should pour out of the slow speed circuit.

I would do the same for every orifice at the top of the carb throat.

Go to the front mount flange and locate the slow air jet tube (inner) and main air jet tube (outer) and blast them both thoroughly watching for fluid to exit the orifices at the top of the carb throat.
If you block the slow speed hole where the tube plugs in it helps to increase flow and scrubbing power.

Ensure that the atmospheric vents are clear. Locate their two holes at the top of the float chamber in the main body and blast them from the inside. Cleaning them from the outside sometimes forces crap back inside them.

If you didn't remove the idle mixture adjustment screw and clear the passage before, you have to decide if you want to do that now or re-install the carbs and try running again. But....if it still doesn't idle or runs like crap, you'll probably be taking them back off and doing that next.
Either way, it's a P.I.T.A.

If you want the Bible on getting these little "jewels" clean and dialed in it's here under Support Materials.


Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com publications.powerequipment.honda.com

Good luck.
Click to expand...
All cylinder have spark, even tried to change coil. I have cleaned out the carb and its open everywere, i need to dubble check the vacuum Events though. But have blasted carb leker through the slow idle jet hole and it comes up nicely inside through the small holes.
 
UPDATE!

Changed oring on slow jet and fave everything and Quick spray with carb cleaner. Now its purring so nicely 😊

So conclusion is that those o-rings on the slow jets are very important that is in good condition.

But now I have learned alot about theese carbs and how to maintain them in the future. Thx for all the input ❤️
 
Glad you got it.

Now it's time to put in the study time on how the acceleration enrichment and decel anti stall system works. It can be confusing if you don't know and have a problem with it.

Good luck.
 
Back
Top