Stalls running at idle speed

[kyounger]

Engine: 2004 Honda 20 horse, 4 stroke
My engine stalls while running at idle speed. When put in nuetral, and start botton pushed, the engines fires right back up, without any hesitation or long periods of turning over, as if nothing ever happened. I have cleaned the carb. I have adjusted the idle speed. I have changed fuel tanks and in line filters. Nothing has helped.
The engine will sometimes also "surge" when restarting, or simply run very rough. After being put in neutral, and setting for a moment, the engine will run fine when put back in gear.
The engine runs fine and strong consistently! Until being run at idle speed, then it cuts out, refires immediately...
Is this a ECM issue?
Any ideas are greatly appreciated! This is driving me crazy! Thanks

 

[ahicks]

If I were being allowed a bet here, it would be that you missed some dirt when you cleaned the carb.

If that were the case, it wouldn't be the first time that's happened. I've cleaned literally hundreds of Honda carbs, and on occasion, will still have one bite me in the butt that will need to be pulled and gone through again.

 

[kyounger]

Would that allow it to run so well, and then stall at idle, and then restart so easily?

 

[ahicks]

Would that allow it to run so well, and then stall at idle, and then restart so easily?

Stalling, running rough at idle speeds would be totally typical...

 

[kyounger]

Thanks much. I'll give it a shot once again! Thanks!

 

[km1125]

Yep, sounds like it's running just a tad lean at idle (surging is a typical indicator). Also make sure you have a good seal between the carb and engine. Just a tiny vacuum leak there will exacerbate or cause a lean condition at high vacuums (idle!). You mention adjusting idle speed, but have you adjusted the idle mixture? Not exactly sure on that carb, but you might have to drill out the cap over the mixture screw. That would also allow you to remove the mixture screw and clean in there too.

 

[kyounger]

KM1125 thanks for the reply. I just came back in the house from running the motor. I removed the carb, soaked it, sprayed it out with carb cleaner, replaced the rubber seal between the two halves, replaced the old fuel filter on the engine, replaced the two gaskets on the spacer between the carb and intake manifold, everything looked great! Ran it in a tub of water, and continued to stall after running two minutes in gear at idle speed... again, it started right back up, then stalled after two minutes.

I have not touched the idle mixture screw. Not really sure where it is. I'll search on line to try and find it's location. I assume that I can adjust this with the motor running? And I assume that backing the screw out will increase the mixture? How will I know when the mixture is right? When it quits stalling????
Thanks much!

 

[kyounger]

In the package with the rubber seal for the two halves, there were two small round rubber orings. I did not remove any when taking the carb apart, and therefore did not put them in either. I believe I noticed a diagram of the carb showing the brass hollow jet sleeve (with multiple smaller holes along the side) in the main jet as having an o-ring on the top of this sleeve (the top being the end where the brass cap screws into the main jet, thus holding everything in place. The obvious question is whether this o-ring is supposed to be there? And if it isn't on, and it's supposed to be, is part of the issue?

Still looking on line to find idle mixture location... TThanks

 

[ahicks]

"I removed the carb, soaked it, sprayed it out with carb cleaner, replaced the rubber seal between the two halves"

That's a nice start, but it's hardly what I would call a thorough cleaning. A thorough cleaning is about a compete tear down and careful inspection.

Does this carb use a small brass tube that runs from the top to the bottom of the carb, right near the carbs center? If so, there's a tiny jet (that controls fuel flow on the idle), inside it, and my bet is it's plugged. It's TINY (about the size of a whisker hair), so don't try forcing a piece of wire though it. It's a pain to clean, so many just replace them. You should be able to see light when looking down the bore of that tube. If you can't see light, it's not clean....

1 of those o-rings goes on the idle adjustment screw, the other is located on the top of that brass tube.

 

[kyounger]

Yes, there is a brass tube that runs in the center of the carb. It has the other brass tube with the holes in ( I tried to describe in earlier post) sliding over it. The tube in the center does have a hole running through it. I am not sure this is the tube you mean though.

I assume this carb also has an idle mixture screw as well. I could not find which screw it is by looking on line. Would it be hinden under a pressed cap on the carb?

 

[kyounger]

I have found out a few things... if the idle mixture screw is hidden under a cap of some sort, there is four caps... which one could it be? There is also a screw with a tab attached to the screw head, that limits it to only a180 degree turn. This screw was set to the most open position, so I assume it was fully open then...

Any help is so greatly appreciated!

 

[ahicks]

I'd like to be more help, but I'm not familiar enough with that carb. My stomping ground is on the 35-90 hp Honda's. Hopefully somebody more familiar with be able to give you a hand.

Too, often parts diagrams can be helpful with that kind of question....

 

[kyounger]

OK, thanks for the help anyway. Hopefully someone will chime in.. I am thinking of taking the carb off, and taking it to the dealer and asking them to point out what I cannot find on line...

 

[ahicks]

Here's the sort of diagram I'm talking about. See #4

https://www.boats.net/catalog/honda/outboard/20hp/bf20d4-lrta-vin-bamj-1100001-to-bamj-1199999/carburetor-auto

 

[kyounger]

Thanks, I saw that and wondered if that needle valve was the idle mixture valve. That is the one that has a tab on the screw head, that limits it's movement to. 180 degrees. That tab keeps the screw from coming out as well. So, I am at a loss as to how to get that out to clean it out.
I am guessing that this is the idle mixture screw. When I had the motor running this afternoon, turning this screw did not seem to make any difference at all. It either needs to come out to clean the opening out or to set it further open for more fuel. Any idea how it comes out, without damaging it? Thanks again.

 

[MattFL]

If you can find the non-USA equivalent of that screw, or maybe a repair part for that screw, then you can replace it with an adjustable one. I did that on my 50. The head breaks off super easy, then use a left handed drill bit or easy out and the screw comes right out since it's not tight. I would second what has been mentioned above about cleaning. Ultrasonic cleaner, carb cleaner and compressed air through every hole and passageway. The holes in those carbs are miniscule and clog very easy, especially the slow speed circuits.

 

[kyounger]

Thanks. I'll check on getting the screw out, and then I'll go back to the cleaning again. Thanks for the help!

 

[ahicks]

Do you have a HD soldering iron or gun? That cap is held in place by epoxy, and if you're VERY careful heating the hell out of it, it will release, allowing the cap to be pulled straight off. Do not attempt to pull at any sort of an angle, or attempt to pry. That's a guaranteed way to break the head off (don't ask me how I know). I have a success rate of about 75%.

If (when?) you do break it off, I generally use a very sharp pick, or better, a #11 Xacto knife around the outside of the screw head to unscrew it. Takes some patience for sure, but I don't remember one that wouldn't come out.

Screw in hand, a dremel tool with a cut off disc can be used to cut a new slot in the screw head. Just don't let it grab, or that screw is going to be tossed into the land of Neverfindum.......

Oh, don't forget there's a spring under that screw head!! They have a habit of traveling to Neverfindum as well.....

 

[km1125]

Thanks, I saw that and wondered if that needle valve was the idle mixture valve. That is the one that has a tab on the screw head, that limits it's movement to. 180 degrees. That tab keeps the screw from coming out as well. So, I am at a loss as to how to get that out to clean it out.
I am guessing that this is the idle mixture screw. When I had the motor running this afternoon, turning this screw did not seem to make any difference at all. It either needs to come out to clean the opening out or to set it further open for more fuel. Any idea how it comes out, without damaging it? Thanks again.

Yep, that would be the idle mixture screw. That cap is an EPA "tamper resistant" cap that doesn't allow much adjustment in the mixture. Take ahicks advice about getting that cap off without damaging the screw, then you can take the screw out and clean it and the passages below it. Also, when you're blowing out the carb, start blowing it out from the engine side, because you want to blow any debris "backwards" out of the carb instead of forcing it further into the small carb passages.

When you're ready to remove the mixture screw, first turn it in GENTLY until it fully seats, counting the turns. Then you know roughly where to put it in when you're reassembling it. Put it all the way in GENTLY, then turn back out the same number of turns.

Once the engine is all back together and running, you can gently turn that screw in until the idle starts dropping, then turn it back out 1/4 of a turn or so until it's idling consistently. You might have to re-adjust the idle speed, then re-adjust the mixture until both are in the right place (idle at the right speed, and mixture just a little richer then the minimum).

 

[km1125]

Just another thought... on the idle mixture screw. If the TAB is the only thing holding the screw from turning completely out, then I'd see if it's possible to just grind or file the tab off without having to remove the complete cap.