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Fuel, fire and compression. and still nothing

#1

PTmowerMech

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?


#2

Scrubcadet10

Scrubcadet10

Do you have spark at the correct time?


#3

PTmowerMech

PTmowerMech

Scrubcadet10 said:
Do you have spark at the correct time?
Click to expand...

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.


#4

Fish

Fish

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


#5

B

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 .


#6

PTmowerMech

PTmowerMech

Fish said:
Have you re-checked the key? Why did you replace the flywheel to begin with?
Click to expand...

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.


#7

PTmowerMech

PTmowerMech

bertsmobile1 said:
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 .
Click to expand...


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.


#8

B

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 .


#9

Hammermechanicman

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


#10

Hammermechanicman

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.


#11

PTmowerMech

PTmowerMech

bertsmobile1 said:
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 .
Click to expand...

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?


#12

C

Chiefsforever46

PTmowerMech said:
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.
Click to expand...

That last statement definently holds true for me. ?


#13

Hammermechanicman

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.


#14

PTmowerMech

PTmowerMech

Hammermechanicman said:
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.
Click to expand...

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. :devilish::ROFLMAO:o_O


#15

Hammermechanicman

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.


#16

PTmowerMech

PTmowerMech

Hammermechanicman said:
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.
Click to expand...

FM?


#17

B

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


#18

PTmowerMech

PTmowerMech

bertsmobile1 said:
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
Click to expand...


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?


#19

Hammermechanicman

Hammermechanicman

PTmowerMech said:
FM?
Click to expand...
F######G Magic ?‍♂️


#20

Scrubcadet10

Scrubcadet10

Hammermechanicman said:
F######G Magic ?‍♂️
Click to expand...
Nice hat and beard.


#21

Hammermechanicman

Hammermechanicman

In
PTmowerMech said:
BTW, do plugs throw a thicker spark at lower RPM's? Say like when one is being cranked?
Click to expand...
We sometimes think a 10,000 rpm 2 stroke engine will have a hard time sparking that fast but in reality it is a non issue. Cranking speed or 14000+ rpm the magneto puts out the same energy. Consider my 1966 396cid chevy with a standard 3 ohm coil and points. Turning at 6000 rpm the distributor is turning 3000 rpm and opening the points 8 times per rev. 3000 x 8 = 24000 spark pulses per minute. Above 6000 rpm you needed a magneto or a dual point distributor. The operating speeds of small engines from cranking speed to 15000 rpm is insignifigant to a magneto ignition. Some chainsaws have speed limited coils. At somewhere around 12000rpm the saw starts "blubbering" and folks think the coil can't keep up when in reality it is designed that way.


#22

B

bertsmobile1

The faster a magneto spins the higher the voltage , the faster the votage rises & more powerfull the spark
IT is the exact opposite to a battery & coil .
Think about adjusting the speed of a generator, too slow & you are undervoltage & too fast and you go over voltage .

The term coil saturation is used to describe the time it takes for a coil to become fully charged and it is a set time
The faster the magneto is spinning the less time is available to do this , so the coils on small 2 strokes are wound to be able to be fully saturated at whatever the operating speed of the engine is .


#23

StarTech

StarTech

Don't get trapped in the illusion. Thinking somewhat outside the illusion helps.

The service manual will provide you a hint of what may be bad....Get a copy of it or someone here that has it should read it and then post the info. Hint: It is in section 7. Bert's and Scrubcadet thinking is on track if this is the cause. Won't be the first time I have seen it.

Also technical bulletin 25.2005 needs to be referenced when comes to the flywheel. The IPL only references one flywheel and ignition coil setup but does note the TB.

Something I haven't needed but I should get it anyways.


#24

PTmowerMech

PTmowerMech

StarTech said:
Don't get trapped in the illusion. Thinking somewhat outside the illusion helps.

The service manual will provide you a hint of what may be bad....Get a copy of it or someone here that has it should read it and then post the info. Hint: It is in section 7. Bert's and Scrubcadet thinking is on track if this is the cause. Won't be the first time I have seen it.

Also technical bulletin 25.2005 needs to be referenced when comes to the flywheel. The IPL only references one flywheel and ignition coil setup but does note the TB.

Something I haven't needed but I should get it anyways.
Click to expand...

The part numbers on the flywheels matched. The engine finally turned over, as I stated before. And after the other flywheel was installed. But not immediately after changing the flywheel. There was still a LOT of pulling and spraying (carb cleaner) before it finally hit.

So, the finally diagnosis was that it was haunted. And I finally pulled on it enough times that the ghost just gave up.


If this small engine stuff doesn't work out, I'm going to be a ghost buster. :ROFLMAO:?


#25

PTmowerMech

PTmowerMech

Well this darn thing is making a fool out of me, still. Got the new carb on and it fired right up. But it just wouldn't adjust right. WOT, while turning the screw would get it spot on. But hold it there (WOT) for about 10 seconds and the tone would change. Let off the trigger and it dies. Just after idling fine for about 5 minutes.
Then wouldn't crank again. Or would crank.

Just fires off when it wants to. Hard to tell by the spark tester if it's losing spark when shutting down. It looks like it's not a spark problem.

Note to tells, don't let your stomach touch the spark tester at WOT. OUCH!!!!!!!


#26

Fish

Fish

I would say that you may have a blown seal, or some other air leak.
So a leakdown test would be something to think about.


#27

Hammermechanicman

Hammermechanicman

Yeah, you need to check the crankcase bolts for being loose and if they are tight do a pressure and vacum test. Also check the impulse hole to the carb is clear.


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