2 Stroke Carb Jet Cleaning

[zenoahphobic]

Small stuff can have a big influence. A common "nail" is a small and seemingly inconsequential part, having little influence. However, remember the proverb:

For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the message was lost.
For want of a message the battle was lost.
For want of a battle the kingdom was lost.

Yes there are many stupid sayings that are totally illogical. Because the nail above has no direct relationship with war.

If you believe the above, then it follows that all those Kingdoms in history that used unshod horses were lost! Count all the horses used in all conflicts and tell me the percentage shod to unshod, particularly pre industrial revolution.

On that point, small having a large affect, the Domino affect can demonstrate that an extremely small domino with gradually increasing sized dominoes (forgot the ratio) can eventually topple an extremely large domino. I mean atomic size up to space size. This is an example that demonstrates that extremely small potential energy can harness very large potential energy.
Many many more examples small creating big (e.g. atomic bomb) but if just a small idle jet is blocked, and nothing else is abnormal included operator input, then the chance for any damage is extremely small if not impossible. Yes big difference to OP, as afterall his engine now responds to his request. The engine on it's own will misfire and if there is enough energy stored in the flywheel may again, but most likely, as in this case, the engine ceases to operate.

[Jason2tpa]

What would yall list as tell tale signs of a rich mix and a lean mix? And then once you've determined either one, how do you determine which mix screw to adjust? My engine S115W has 4 mix adjustment screws. Or if its running rich or lean you would adjust all 4 accordingly?

I know to most of yall this is carb 101, so I appreciate your time.

Not all doubting that lean conditions caused a pop causing the damage you have seen, but suggest that it is relatively rare and that more often than not there are other contributing conditions surrounding.

[TownsendsFJR1300]

Ethonol absorbs water.

Water now accumulates in your tank.

Water in the fuel doesn't burn.

Water in the system also helps corrode your fuel system.

Put a small jar of new ethonol fuel (from a sealed container) out in the open air. You can literally watch it turn foggy as it collects water from the air.


An interesting video re the K100 I use:
The third video down:

Demonstration | Fuel Additive | K-100

It should be noted that since going to non-ethonol ONLY and the K-100, I have NEVER since, drained a drop of water from my engine, transom filter-see thru, etc. The fuel tank is original (from 1997) and never pulled/cleaned, just drained the one time (mentioned before) and NO water was found..

Snake oil, maybe.. But I don't have ANY WATER ISSUES-NONE...

[TownsendsFJR1300]

What would yall list as tell tale signs of a rich mix and a lean mix? And then once you've determined either one, how do you determine which mix screw to adjust? My engine S115W has 4 mix adjustment screws. Or if its running rich or lean you would adjust all 4 accordingly?

I know to most of yall this is carb 101, so I appreciate your time.

Your shop manual will have the spec's for what the # of turns out should be from lightly seated. Some carbs, same engine, have different settings for those screws (which I learned here)..

Unless your altitude is way up there, plugs are black/fouling, engine runs like the choke is on, the factory spec's should do you fine.

[zenoahphobic]

What would yall list as tell tale signs of a rich mix and a lean mix? And then once you've determined either one, how do you determine which mix screw to adjust? My engine S115W has 4 mix adjustment screws. Or if its running rich or lean you would adjust all 4 accordingly?

I know to most of yall this is carb 101, so I appreciate your time.

You make two interesting points.
As far as determining too lean versus too rich - a short answer will not suffice.

Your second point on how do you adjust: short answer is that adjustments are gradual, because we tend only to have the capacity to adjust one thing at a time, and have to make a decision on which to start on first, and that we want the engine to continue running as we alter settings. That is why we often need to refer to manufacture's procedures, because there are base or static starting adjustments (engine dead) and dynamic adjustments (engine running). The order of adjustments and the extent of adjustment is often behind the difficulty in getting the required results, or the worsening of the problem.
This is just an academic answer to your post.

[boscoe99]

What would yall list as tell tale signs of a rich mix and a lean mix? And then once you've determined either one, how do you determine which mix screw to adjust? My engine S115W has 4 mix adjustment screws. Or if its running rich or lean you would adjust all 4 accordingly?

I know to most of yall this is carb 101, so I appreciate your time.

You got four screws. You got four carburetors. One for each motor. If you consider that your model has four separate motors that are driving a common crank shaft.

The screws adjust mostly just the idle mixture. Changing the main jets can be done to adjust the power mixture.

Idle mixture screws are usually adjusted first to the manufacturer's specifications and from there as needed to achieve a particular idle quality. The idle mixture jets (aka pilot or slow jets) can also be changed. Main jets can be adjusted by changing the jet size to enrich or lean the mixture at power.

The spark plugs can be "read" so as to determine if the mixture at power is rich or lean. That can be more of an art than a science. Remember back in the days that Nascar used carburetors they would run the car at WOT and then cut the ignition off. The car would coast in with a dead engine at which time the plugs would be removed to determine if the carburetor was running rich or lean at power.

Now consider this. What happens in a piston airplane motor as the air plane climbs in altitude? The carburetors on them have an adjustment so that the pilot can lean the engine out as the altitude increases. Some carburetors have an automatic device to do the task for him.

[zenoahphobic]

Small engines, particularly twostrokes have high speed mixture adjustments just like idle. Generally the high speed is adjusted first, at WOT full load (albeit difficulty in setting that environment) to achieve the greatest power by max rpm.
Idle mixture is similarly adjusted to get maximum speed at idle. This requires idle stop screw adjustments to keep the correct idle speed.
This is fundamentally simple and has no regard for emissions or operating temperatures for that matter.
Modern engines fiddle with mixture ratios that may not be ideal, but are there to meet other criteria.

[zenoahphobic]

I should have also added where there were fixed main jets on carburettas that have no float chamber, to control the full power mixture, these jets were a little oversized, and the fuel flow was fine tuned with a "tap" in the fuel line.

[Jason2tpa]

That's a really simple way to think of it...4 screws, 4 carbs, 4 motor. But here is when I get messy. I'll give you the scenario, you guys tell me if its the right or wrong adjustment:

Assuming the 4 idle mix screws are set to spec and the engine is warm. The rpms in neutral (idle) are below spec, lets say 500. Engine sounds like it could kill. I adjust the throttle screw in, thereby increasing the rpms to spec. Right or wrong?

You got four screws. You got four carburetors. One for each motor. If you consider that your model has four separate motors that are driving a common crank shaft.

The screws adjust mostly just the idle mixture. Changing the main jets can be done to adjust the power mixture.

Idle mixture screws are usually adjusted first to the manufacturer's specifications and from there as needed to achieve a particular idle quality. The idle mixture jets (aka pilot or slow jets) can also be changed. Main jets can be adjusted by changing the jet size to enrich or lean the mixture at power.

[zenoahphobic]

Jason, true but then you go back to the idle mixture screw to get good max idle, and back and forth if necessary. Every adjustment in theory affects other adjustments (tuning). However in your case, I doubt that you will be able to replicate your earlier blocked jet problem . Those adjustments are really for idle.
Just as a different point of view on the lean issue, calculate the area of that 0.016 jet, and compare that area with your calculation of the main jet area, that ratio will give you a rough clue on the overall influence it has on the power of the engine. I suggest at load 3300rpm there is more reliance on the fuel going through the main jet than that going through that idle jet.
Some may come back here and argue against what I said.
On the issue of "lean sneeze", by definition it implies something insignificant. It to me is a small misfire, caused by little fuel and therefore small energy. That is little fuel. Distructive lean conditions , which is often confused with this , occurs with lots of fuel and even lots more air.
Another problem is that rarely would someone have a "lean sneeze" and immediately tear down the engine to inspect possible damage. A mechanic goes on third party descriptions of events, and so often does not witness "sneeze" and sees the resultant damage.
I always wonder how doctors spruik things when they are not only faced with amature anecdotal evidence and little customer feedback post consultation (do they just assume their treatment was OK because the patient has not returned- they could have gone to a better doctor or have died).

[TownsendsFJR1300]

Assuming the 4 idle mix screws are set to spec and the engine is warm. The rpms in neutral (idle) are below spec, lets say 500. Engine sounds like it could kill. I adjust the throttle screw in, thereby increasing the rpms to spec. Right or wrong? CORRECT

The mechanical linkage and stop screw (NOT air screws), for that low idle, yes should be adjusted clockwise to raise the idle.

The air screws on each carb are for fine tuning (smooth, steady idle) NOT for raising idle major amounts.

*All this is assuming you have done the proper link and sync for your particular model FIRST.

[rodbolt17]

and if you study the design of the carb you will find there is NO A/F adjustments.
you can allow more or less of the fixed A/F ratio. but you cannot change it with a screw.
the A/F ratio is fixed by the pilot air jet and the pilot fuel jet.
set it where the book says and it works or the engine has an issue.

[boscoe99]

Small engines, particularly twostrokes have high speed mixture adjustments just like idle. Generally the high speed is adjusted first, at WOT full load (albeit difficulty in setting that environment) to achieve the greatest power by max rpm.
Idle mixture is similarly adjusted to get maximum speed at idle. This requires idle stop screw adjustments to keep the correct idle speed.
This is fundamentally simple and has no regard for emissions or operating temperatures for that matter.
Modern engines fiddle with mixture ratios that may not be ideal, but are there to meet other criteria.

I forgot about the high speed mixture adjustment screw on some motors. My chain saw has one.

Damn thing ran like crap when I bought it new. If I could get it running. Had to buy the mixture adjustment tool to enrich the idle mixture setting. The hell with the EPA.

Starts on no more than two pulls now and runs like a champ.

[99yam40]

A lot of the small air cooled 2 stroke motors on tools have high speed adjustments, but there are some that do not. Echo is one brand that did not.
I like to be able to adjust both high and low.

seems the older carbs that did not have the purge bulbs were easier to deal with.
did not have those little plastic/rubber check valves that are easy to screw up with the wrong cleaner or air pressure while cleaning passages

[TownsendsFJR1300]

I forgot about the high speed mixture adjustment screw on some motors. My chain saw has one.

Damn thing ran like crap when I bought it new. If I could get it running. Had to buy the mixture adjustment tool to enrich the idle mixture setting. The hell with the EPA.

Starts on no more than two pulls now and runs like a champ.

I see that ALL THE TIME. It needs to be fattened up just a tad.

The adjustment screws are usually recessed in the aluminum carb body.

**If I don't have the correct tool, I simply take my dremel, cut a thin slot thru the recess and keep going until I cut a small screw driver slot in the adjuster. NOW, I can adjust anytime, anywhere with a small screw driver...

And with that said, I use a small Echo tach:
Echo ENG TACHOMETER [99051130017] for Echo Lawn Equipment | eReplacement Parts
(I didn't pay that much for it) and with that can easily get another 1000-2000 RPM's with the adjuster using the tach for fine tuning.

My weedeater now gets about 8,000 RPM WOT. Before, maybe 6,000