Low speed adjustment

[Newyota]

At what point does the low speed screw/setting become a non factor?As you increase throttle position Can I Assume it still delivers fuel,but the high speed jet just makes up the difference it needs for increased rpms..Any insight is appreciated..

 

[ondarvr]

Correct, it's effect is 100% at idle, at just above idle it becomes almost irrelevant.

 

[oldboat1]

^^^agree with ondarvr. Part of idle mix setting, though, is to insure smooth shifting and throttle up (no stalling) -- think that is consistent with what you are describing in the switch over.

 

[jimmbo]

Since 2 stroke carbs don't have accelerator pumps the low speed mixture is quite relevant, Also, on larger engines, there is very little opening of the carbs until the after the timing is fully advanced so if the throttle lever is not pushed enough to start opening the carb, the carb is supplying fuel thru the idle and off idle fuel circuits. Running the engine at 1500 rpm, try adjusting the low speed needle, the engine will respond

 

[bruceb58]

At what point does the low speed screw/setting become a non factor?As you increase throttle position Can I Assume it still delivers fuel,but the high speed jet just makes up the difference it needs for increased rpms..Any insight is appreciated..

once the throttle plate starts to open and the vacuum draw on the idle circuit diminishes, little or no fuel comes out of the idle circuit. Probably still involved at 1500RPM as jimbo said but not much after that if any.

 

[Newyota]

Thanks..good info...Now I have been reading about and saw videos of motors wth a "lean sneeze" ..that sounds like a loud intermittent knock in the engine.I hope that's all it is?Is this mainly due to low speed setting?When I last had my 85' 25hp on the muffs I think I had this as I would throttle it up and then it went away say at half throttle or close to it.I want to get it on the water to try and tune it with back pressure on it and so I can get it up to op. temp.Waiting for some better weather here to get it on the water.I had time to go thru the CDI/stator resistance checks for the first time and checked out good according to the CDI website.

 

[jimmbo]

A "lean sneeze" sounds like a sneeze. knocking sounds, are something else. Revving up an engine while on muffs is a sure way to transform it into an anchor,

 

[Newyota]

ok-Could a lean sneeze sound louder on muffs and I mistake it for a knock?Not sure what I have then in that case.I am definiatley getting an education lately with this and 9.9hp I recently worked on.What could make a knocking intermittently if it is not a fuel/misfire or igniton issue?Would a rod knock be constant?Someone else suggested running it with the lower unit off.May have to do that.Have to just work thru it.I could hear a noise last year after I bought it while on the water at slow speed with the cover on of course, but was not sure what I was hearing.My motor lock was kinda making a rattle noise so I may have heard acouple different sounds so I removed it for this year to test also..I will find out.Have too much invested in this thing.Figured I paid too much once I really got into it.Oh well!Time will tell.Got to test my 9.9hp now after the water impeller job today.I may need it!

 

[lindy46]

Here's a lean sneeze:
https://video.search.yahoo.com/sear...07462d37c6c8a173946e4f7807ca0ce8&action=click

 

[Newyota]

I think I watched that after I ran my motor.That is where I got the lean sneeze idea from.I had found another one also that was similar.It does give a knock like I described mine does, but mine was out of the water on muffs that may have made it sound worse due to lack of back pressure.thanks for getting back to me.

 

[Newyota]

Finally got the motor down to the river to get it in the water to test. Started first pull now I unplugged the primer orifice on carb.,new plugs and I gapped them at .40 per some advice and knock no longer there.Pretty sure it was the lean sneeze just sounding much louder out of the water on muffs..Was working on the slow idle/speed screw and being in the water is really by far best way to do this due to back pressure.PO had the screw only an 1/8th open and it was running this way and I had no idea how to adjust it last year till now that I had time to delve in to it..