Fuel, fire and compression. and still nothing

[PTmowerMech]

You can flood an engine with sprays every bit as much as you can with a liquid fuel
Next time you find yourself in this position try warming the plug & / or the cylinder with a hot air gun.
The fuel : air mix burns at the same speed regardless of what it is in or how fast the engine is spinning.
So to burn completely before the exhaust port opens, high speed 2 stroke engines need a lot of advance .
With a timing chip, this is actually retard because at STP you can slow electricity down but you can't speed it up.
So with most 2 strokes the timing at starting is right on the verge of being too far advanced thus it becomes critical that it is exactly right.

On 4 strokes that are only spinning at 1/2 to 2/3 of a two stroke the timing is no where near as critical .

Ok (with the exception of flooding), that doesn't explain how if there's fuel in the chamber, and spark, that there's not at least some sort of explosion. If I'm understanding your right, you're talking about things working as they're supposed to. But I'm still confused as to how there's no explosion. '
Or is there one, and it's just not audible?

 

[Chiefsforever46]

I understand what you're saying. The confusing part was that maybe what I thought I knew, was wrong. The coil can only get juice when the magnets pass the coil at a certain distance from the leg. And the coil, with a good key, is only going to allow the correct timing.

With a broken key, and carb cleaner, seems there would be some sort of hit, even with the timing 90 degree's off. If gas gets spark, regardless of where the piston is, there's gonna be an explosion. That's what I was trying to get.


And after taking the cover off again, looking at where the magnets were crossing the leg, and seeing the flywheel key still in tact, I did the same exact thing as I did for the first 200 pulls. Spray just a little carb cleaner into the carb, and pulled it about 4 times. Except this time, it fired off.
Why this time, and none of the other times? I can't say. I'm pretty embarrassed for making this thread now.

2 cycles hate me.

That last statement definently holds true for me. ?

 

[Hammermechanicman]

Liquid gasoline does not burn, gasoline vapor burns. If you put liquid fuel in the plug hole you run the risk of wetting the plug to the point that is arcs through the liquid fuel and no combustion.

 

[PTmowerMech]

Liquid gasoline does not burn, gasoline vapor burns. If you put liquid fuel in the plug hole you run the risk of wetting the plug to the point that is arcs through the liquid fuel and no combustion.

Yes, that's pretty commonly known. But after many pulls, especially with no other source of fuel (empty tank and clogged carburetor), then eventually the air coming through the carb is going to dry out enough that only vapor is left. And with spark, there's going to be fire. Like I said, I pulled on this darn thing at least 100 times.

When it finally fired off, it was from doing the same exact thing as I'd done many times before. Sometimes, I'd even sprayed less carb cleaner in it than the time it fired.

I guess what I'm looking for here, is for someone to go along with the idea that this thing not only hates me. But the ghost that possesses it, also hates me.

 

[Hammermechanicman]

Oh hell, i have worked on lots of demon possesed evil 2 strokes that hated me. Those things are a given. I have a voodoo priestess on retainer to cast out the demons. Only way to fix some of them. Sometimes you have to use FM on them.

 

[PTmowerMech]

Oh hell, i have worked on lots of demon possesed evil 2 strokes that hated me. Those things are a given. I have a voodoo priestess on retainer to cast out the demons. Only way to fix some of them. Sometimes you have to use FM on them.

FM?

 

[bertsmobile1]

New spark plugs have no glaze on the insulator nose inside the plug.
Modern fuels are conductive at cylinder pressure .
So the liquid or excessive spray condenses on the insulator providing a conductive path to ground so no spark inside the cylinder thus no bang.
Once this has formed you usually have top burn it off
The electrical resistance of air increases by the square of the pressure .
Those old Champion spark plug testers you sued to see in service stations who sold 3 times as many spark plugs than they should gave worked by increasing the pressure till eventually the spark stopped.
You spun the dial to show the customer that their spark plug was faulty at working pressure the sold them a new one .
It is the same principle as the moving gap magneto testers
In air a good mag will throw a spark from 1/4" to over 1" but inside the engine it will be lucky to jump a 0.050" plug gap .

Now because small 2 strokes start at higher compressions than mowers and run at faster speeds the coils are wound to produce optimum power at 7000 rpm or higher.
Thus the sparks at cranking speed is quite feeble
If they produced a big fat spark at cranking speeds the coil would burn out when running full speed

 

[PTmowerMech]

New spark plugs have no glaze on the insulator nose inside the plug.
Modern fuels are conductive at cylinder pressure .
So the liquid or excessive spray condenses on the insulator providing a conductive path to ground so no spark inside the cylinder thus no bang.
Once this has formed you usually have top burn it off
The electrical resistance of air increases by the square of the pressure .
Those old Champion spark plug testers you sued to see in service stations who sold 3 times as many spark plugs than they should gave worked by increasing the pressure till eventually the spark stopped.
You spun the dial to show the customer that their spark plug was faulty at working pressure the sold them a new one .
It is the same principle as the moving gap magneto testers
In air a good mag will throw a spark from 1/4" to over 1" but inside the engine it will be lucky to jump a 0.050" plug gap .

Now because small 2 strokes start at higher compressions than mowers and run at faster speeds the coils are wound to produce optimum power at 7000 rpm or higher.
Thus the sparks at cranking speed is quite feeble
If they produced a big fat spark at cranking speeds the coil would burn out when running full speed

The first part of this, are you saying that the fuel is actually grounding out the tip of the plug?


BTW, do plugs throw a thicker spark at lower RPM's? Say like when one is being cranked?

 

[Hammermechanicman]

FM?

F######G Magic ?‍

 

[Scrubcadet10]

F######G Magic ?‍

Nice hat and beard.