I have a 2000 Yamaha Kodiak 400 that I have had since 2002. I have ridden lots of miles and done (I am sorry to say) virtually no maintenance to it. Late last fall (nearly 2 years ago), I was using it around the farm and it was running fine. After shutting it off for a few minutes, I went to start it and it backfired, blowing the boot off the carburetor (between the engine and carburetor). Try as I might, I could not get it to start after that.
Fast forward (past a shoulder surgery, and many months) and I have been trying to get it going again. I have replaced the carburetor (with a cheap ebay carb) and the spark plug. I have replaced the gas with brand new, super unleaded (non-ethanol). I changed the oil and took off the valve covers and they appeared to be working.
It turns over fine and the spark plug sparks when grounded to the frame or engine.
When I put my finger over the spark plug hole, it is pushing air out when I turn it over and it is pulling air through the carburetor. The carburetor is taking fuel, and (assumedly) injecting it into the engine. There is air (and gas smell) coming out the exhaust.
When I remove the plug, it is not very wet, and only faintly smells of gas (sometimes) and other times smells more like vanilla (yes, like a candle and I have had a friend verify this).
The connections between the carb and engine have been checked for leaks, cracks, holes and are tight.
I have tried pouring gas into the spark plug hole. I have tried spraying starting fluid into the plug hole and into the carburetor. I have tried the starter, for minutes at a time, with the choke on, or the choke off.
Nothing that I have done makes any difference at all.
The only exception to that is when I have sprayed a LOT of starting fluid either into the carburetor, or directly into the head (with the carb removed), after a couple minutes of turning over, it will finally ignite the starting fluid on top of the engine, or in the air cleaner box (depending on which way I did it). The engine never, pops or lets out exhaust smoke, not at all.
A google search suggested the following things:
Incorrect valve clearance "as the engine gets some hours on it, the valves may seat deeper in the valve seats and need adjusting".
The timing is off/the flywheel timing key is sheared. (I'm not even sure that it has one of these.)
So, any thoughts/suggestions?
Thank you so much!