2 Stroke Carb Jet Cleaning

[99yam40]

Higher RPM is not the only thing when tuning.
need to make sure when loading up it has the fuel needed to make the power.

lean can get higher RPMs, but need to give it a little more fuel to make sure it does not overheat and still carry the load

[boscoe99]

Best power comes from a richer mixture anyway. Not stochiometric and certainly not leaner than that.

[Jason2tpa]

Ok guys, great info. I wasn't familiar with the phrase "lean sneeze". I assume it means a combustion "pop" sound. Yesterday was the first full day of running the motor after cleaning the jets. I noticed a faint pop sound immediately after motor fired up. Emphasis on the word faint, definitely not loud. And it didnt occur after every ignition, maybe 1 out of 5. This sound coupled with a low idle rpm implies the mix is lean, correct?

[99yam40]

From what I have heard the lean sneeze is when the fuel/air charge gets so lean it goes off in the crankcase before it enters the cylinder.

reeds try to contain it and keep it from blowing back into the carbs.
it can hurt the reeds, crankcase seals, and fuel pump diaphragms if they are connected to the crankcase that goes off. Crankcase seals etc. are not designed for that kind of pressure rise

[scofflaw]

From what I have heard the lean sneeze is when the fuel/air charge gets so lean it goes off in the crankcase before it enters the cylinder.

reeds try to contain it and keep it from blowing back into the carbs.
it can hurt the reeds, crankcase seals, and fuel pump diaphragms if they are connected to the crankcase that goes off. Crankcase seals etc. are not designed for that kind of pressure rise

How does the spark get to this mixture ? How do explain the same sneeze in a 4 stroke ?

[boscoe99]

A lean mixture will burn much more slowly than will a correct fuel mixture. The combustion process is still going on when the piston uncovers an intake port or an intake valve opens. The still burning combustion mass lights up the new air/fuel charge.

In a two stroke the combustion now takes place within the crankcase. Reed valves can be damaged. In a four stroke combustion can take place in the intake manifold all the way to the EFI throttle body or the carburetor. In a four stroke it is typically referred to as a back fire since fire is coming back out of the motor the wrong way. Not to be confused with after fire.

You guys won't know but the little girls understand. I am a back door man.

[TownsendsFJR1300]

Higher RPM is not the only thing when tuning.
need to make sure when loading up it has the fuel needed to make the power.

lean can get higher RPMs, but need to give it a little more fuel to make sure it does not overheat and still carry the load

I set those carbs for the highest RPM's, then slightly richer, just a knats hair. And when adjusting it, making sure it fully to temp as it will change slightly from warmed up to have been running for an hour...

[99yam40]

You guys won't know but the little girls understand. I am a back door man.

Way more info than I needed

[zenoahphobic]

It's funny how you runaway with enthusiasm, partially small engines.
I used port and polish my two stroke lawnmower. When that didn't turn it into a grass eating monster, I made an expansion chamber for it.
Needless to say a waste of time, you can't make a Grand Prix motorcycle out of a Moped.

[TownsendsFJR1300]

It's funny how you runaway with enthusiasm, partially small engines.
I used port and polish my two stroke lawnmower. When that didn't turn it into a grass eating monster, I made an expansion chamber for it.
Needless to say a waste of time, you can't make a Grand Prix motorcycle out of a Moped.

If that's for me, just passing along tips I've learned over the years. Stuffed the empty crankshaft holes (in single 125 and 250 Yamaha two strokes-YZ's, Motorcycles) back in the day too...

A dealership will charge you more to LOOK at the machine, VS just adjust the HS air screw out a hair (BS)..
My fav weed eater was a freebee in exchange for some work on another machine. Needed fuel lines, carb cleaning, etc. It's about 10 years old and runs like a champ once repaired. $0.00 invested short of fuel line which I buy in bulk..

Look at the newer machines.. There are NO carb adjustments, even recessed... I guess you pitch it after a year or two when it runs too lean, idles high and has no high speed power...

I still have a chipper / shredder with an 8 HP Tecumseh engine that ACTUALLY has a high speed adjustment screw below the float bowl as well as a side idle air screw AND throttle stop screw... Try to find that nowadays..

[Jason2tpa]

I set those carbs for the highest RPM's, then slightly richer, just a knats hair.

Noted. Now once I reset each of the 4 pilot screws to spec (5/8 +- 1/4 turn out) do I also unscrew the throttle screw so there is no "added" throttle?...basically starting from scratch, no mechanism added to increase or decrease rpms.

[99yam40]

Noted. Now once I reset each of the 4 pilot screws to spec (5/8 +- 1/4 turn out) do I also unscrew the throttle screw so there is no "added" throttle?...basically starting from scratch, no mechanism added to increase or decrease rpms.

he was referring to his weed wacker 2 stroke motor

[TownsendsFJR1300]

Noted. Now once I reset each of the 4 pilot screws to spec (5/8 +- 1/4 turn out) do I also unscrew the throttle screw so there is no "added" throttle?...basically starting from scratch, no mechanism added to increase or decrease rpms.

Set your air screws, as noted above, to factory spec.

If all your linkages between the carbs are set correct, now simply turn up the physical throttle butterfly stop screw until you get to your desired RPM.

You'll need some turns in as it won't idle with the butterflys completely closed...

Now, if you want to dink with the air screws (within their limits) for a smoother idle, off idle acceleration, that's fine...


And that high speed adjustment post earlier was for a weedeater, not an outboard engine..

[Jason2tpa]

Set your air screws, as noted above, to factory spec.

If all your linkages between the carbs are set correct, now simply turn up the physical throttle butterfly stop screw until you get to your desired RPM.

You'll need some turns in as it won't idle with the butterflys completely closed...

Now, if you want to dink with the air screws (within their limits) for a smoother idle, off idle acceleration, that's fine...


And that high speed adjustment post earlier was for a weedeater, not an outboard engine..

Perfect. Simple explanation, thanks bud.

[TownsendsFJR1300]

Yep, no fancy pictures, basic, easy to understand information...