Fuel, fire and compression. and still nothing

[PTmowerMech]

BG55 blower I'm just checking things out before I start fixing things. (the carb replacement)

120lbs of compression (tested 3 times)
Good spark. Replaced the flywheel with a used one.
Removed the spark arrestor.
I've used carb cleaner in the plug and got nothing.
Poured a little mix into the plug hole and still nothing.
Also tried putting those things through the carb.

Those things are proven to work. I'm not worrying about it running right, right now. Just want to get it to crank, even for just a seconds. Am I'm missing something?

 

[Scrubcadet10]

Do you have spark at the correct time?

 

[PTmowerMech]

Do you have spark at the correct time?

I don't know how to check that. If the flywheel key is in the cranks slot and tight, then it's timed, right? I did regap the coil. But as I said, I'm getting good spark. The testers light is bright enough to see it good in the day light.

 

[Fish]

Have you re-checked the key? Why did you replace the flywheel to begin with?

 

[bertsmobile1]

Think about it PT,
You have been doing this for long enough now
\The magneto coil generates the power for the spark
There is nothing to store that power on most engines so it has to happen just before TDC
So the magnet needs to be just passing the coil then the piston is at TDC for the timing to be good enough to at least get a bang out of it.
Generally the magnet will be just past the trailing leg of the coil.
ANd this is the same for every engine you have worked on except those with some sort of a SAM module or a capacitor.
Have a look at some of the stuff you have around there that works.
The amount the coil passes is different for 2 leg & 3 leg coils but most are around about the same amount in degrees of rotation, type for type .

 

[PTmowerMech]

Have you re-checked the key? Why did you replace the flywheel to begin with?

Because it was soooo small, that It looked like it might have been chipped off. The one I replaced it with, wasn't any bigger. But since I already had the OEM one off, and the other one in hand, I just used it.

 

[PTmowerMech]

Think about it PT,
You have been doing this for long enough now
\The magneto coil generates the power for the spark
There is nothing to store that power on most engines so it has to happen just before TDC
So the magnet needs to be just passing the coil then the piston is at TDC for the timing to be good enough to at least get a bang out of it.
Generally the magnet will be just past the trailing leg of the coil.
ANd this is the same for every engine you have worked on except those with some sort of a SAM module or a capacitor.
Have a look at some of the stuff you have around there that works.
The amount the coil passes is different for 2 leg & 3 leg coils but most are around about the same amount in degrees of rotation, type for type .

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.

 

[bertsmobile1]

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 .

 

[Hammermechanicman]

I personally don't like the put a few drops of gas in the spark plug hole on 2 strokes. Just too easy to get a wet plug and then no fire. I prefer to use actual starting fluid (ether) in the carb. Troubleshooting a no fire problem with 2 strokes can be difficult. Some folks say you will burn up a 2 stroke using starting fluid because it has no oil in it. I have worked on lots of 2 strokes for lots of years and haven't burned one up yet. Little piston port engines are very easy to "flood" which is raw fuel laying in the crankcase. I Have customers bring me equipment every spring where they over choked it or put fuel mix in the carb throat and now won't fire at all because the plug stays wet. A small amount of ether is better than dumping fuel in the engine for troubleshooting.
$00,02 worth

 

[Hammermechanicman]

Also, be careful swapping coils and flywheels on Stihl products. Some chainsaws have 3 different coils that look identical but have different retard and curves. Same for other stihl equipment. Folks get a tuneup kit off ebay that has a new coil so they change it. Those kits ususally have first gen version coils. stihl likes to change coils and flywheels during a products life. Quite often the wrong coil runs with no power or will spark but at wrong time and not start or fire.