Bike Has Spark, Won’t Start

Ok. Will be working on removing the cylinder and inspecting things this weekend. Will try liquid gasket as it is what I have on hand. Will report back later.
 
Rather than making gaskets, I ordered some new ones. Just waiting for them to arrive. Will then open things up and see what we see.
 
So the gasket replacements are all done. All gaskets have been replaced, except the one in the middle of the engine. Proper foot lbs on the cylinder head. No go. What else could be causing this thing to not even attempt to fire?
 
This has me scratching my head, can you check the compression with a gauge? If it has fuel, compression and fire at the correct time it should run. Are you using the stock carb or the replacement?
 
Stock carb now. No gauge to test compression, but I may get one. My son recently got a book about two cycle engines and it has a troubleshooting section that I did not see before which has some suggestions that may help us figure this out. I’m going to be working through this over the next few days and see what I can figure out. I will report back here later.
 
I looked an did not see anything said about the condition of key and keyway that is critical for the spark timing. You check that? I know Briggs 4 stroke engines mostly, so may not apply with 2 stroke engine.
 
We haven’t touched the magneto and the spark plug was firing properly before our issues started. I am not sure timing would apply? Unless something can go out of whack on its own in this area on a two stroke. To me the issue still seems or had seemed related to fuel not reaching the chamber. I still think that is somehow the issue here. I’ve got some other things to try now and will be reporting back here later in the week.
 
Next I would change the magneto coil and cdi, changing both will cut down on troubleshooting. I know you said it has spark, it could be weak.
 
If you have a vendor you prefer try them, I haven’t seen any difference except in the coils, the older style had a white wire that needs to be capped off, the new style only has the blue and black. I’ve bought from eBay and from the vendors here on the forum.
 
As stated above check the key under the magnet, if it’s sheared the timing will be off, it will fire but not at the correct time.
 
This is one of those situations that is probably a very easy fix (if you can see the bike in person)... :/

I commend Greg for taking so much time on this one!



If you can actually see a spark jumping across the plug?, I wouldn't bother replacing the magneto (the part inside the engine).

The only suggestion I have left would be to change the CDI (black box)... I once had a bike that wouldn't start (& it had a good visual spark), but something went wrong inside the CDI that changed the spark timing... Replacing the CDI fixed the problem.
 
The key under the magnet is a woodruff key, or half moon key, with the piston at TDC the key should be at approximately 1 o’clock as in the picture.
 

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