Lean cough? or too rich?

[JerEazy2]

In my previous posts i've rebuilt the carbs as per the manual and also set the timing as per the manual. I have to say that the engine is generally running fantastic. That being said, a new issue has developed. I assume because of my recent work. But you can tell me right or wrong.

While at idle for a short period of time, and not in gear (Like idling at the dock while the wife and daughter run to the bathroom, or putting the boat in idle waiting for someone to pass a narrow channel) every so often i'll get a little cough from the engine. Sometimes its just the once and then it's gone like nothing happened, and sometiems it'll cough and the engine will die like someone turned off the key.

my search of the interwebs says this is called by a lean condition. But i also heard that it could be caused by the carbs "loading up" while idling too long, and it is just something that "happens to carb'd 2-strokes".

I'm not a big fan of the "just deal with it" style of boating. So i wanted to toss it to the experts.

My A/F screws are all set at 1.25 turns out from a soft seat. The manual does state that that can be +/- .25 turns. But it does not go into how to properly set them. Would this be the same as old carbs where you just turn them out or in until it sounds better and then when it starts to stumble back it a bit. And then move onto the next and the next and the next? If so, after you do 1, you do 2, then you have to go back and reset 1 before moving to 3. After 3, go back to 2 and retest, etc etc.

Or, is there another potential issue at play? Improper sync of the carbs allowing too much/not enough fuel at idle?

Thanks again!

[walleye1]

What is it be sides a yamaha 2 stroke? Need the primery Id and horse power.

[99yam40]

lean sneeze at idle sounds like what is happening.
At least one of the cylinders is too lean.
I would back out each 1/4 turn one at a time or all at once to see if that solves the problem.
if the spec setting does not help then I would look into re cleaning the carbs or look for a vacuum leak

[JerEazy2]

sorry Walleye..

1996 S150TXRU.

Should probably just have this in my signature haha.

[JerEazy2]

lean sneeze at idle sounds like what is happening.
At least one of the cylinders is too lean.
I would back out each 1/4 turn one at a time or all at once to see if that solves the problem.
if the spec setting does not help then I would look into re cleaning the carbs or look for a vacuum leak

Rebuilt the carbs less than a month ago (and they needed it!) and i did notice that when i was turning in the screws to check the setting originally, some were almost 2 turns out.

And thank you for the advice on turning them out as opposed to in. I wasn't sure which direction to correct a lean condition. i should be able to check that at some point next week. So we shall see!

Thanks again.

[walleye1]

1 1/4 is what my book says, turn them out 1 3/8 to 1 1/2. I whould have it in the water tied up and in foward gear at idle an see if the idle changes.
Remember you have it tied up so dont rev it up.

[boscoe99]

With my old two cylinder single carburetor Mercury you could really feel the change with an adjustment to the idle mixture screw. Turn it in a tad and it would start to cough (lean sneeze). Turn it out and it would stop, but the idle quality was not as good as it was when on the lean side. Sounded funny. I just had to live with the idle quality being what it was. Lean sneeze can damage some stuff. And a lean idle mixture can affect the high speed carburetor mixture. Last thing to have is a lean high speed mixture.

Now in a six cylinder six carburetor model it is not so easy to adjust just one carburetor and hear/see/feel/smell the difference. IMO. I would simply turn them all out 1/4 turn and see if the cough/sneeze goes away. If not, out another half turn. If it take 3/4 turn then so be it. If 3/4 turn does not do it I would clean the carburetors.

[JerEazy2]

Thank you boscoe.

You addressed what i was curious about - would i actually hear any adjustment with 1 of 6 carbs being adjusted?

before i back them all out the extra 1/4 turn i'll screw them back in and confirm they are all actually out the full 1.25. If they were, i'll back them out the extra .25 and see how she goes.

My next trip is up to the Homosassa river and surrounding waters. This time of year there are a lot of slow/idle speed zones and a coughing/sneezing/dying engine would make for an annoying trip.


Walleye:

Are you supposed to adjust the idle air screws while in gear? I know that's what you're supposed to set the idle speed. But didn't think the screws were supposed to be done that way.

[walleye1]

Are you supposed to adjust the idle air screws while in gear? I know that's what you're supposed to set the idle speed. But didn't think the screws were supposed to be done that way.


I always do it that way, better to have a load on it.

[walleye1]

It helps to have back preasure on the exaust and a load.

[TownsendsFJR1300]

Often, in the owners manual, it'll say "idle set in gear".

Definitely in the water with back pressure, especially on a two stroke..

[JerEazy2]

i guess it makes sense. The Idle Air Screws need to be set along with the idle. Idle gets set in gear, so screws should be set in gear too... Ah well, couldn't hurt anything i guess.

[boscoe99]

The air bleeds are fixed. No adjustment.

[99yam40]

pilot screws adjust the amount of fuel and air mix that gets dumped into the carb during idle

[boscoe99]

Wait for it. It is coming.