Cowboy Sailor already came up with the best test to see if it's a carb problem or not. Try some starting fluid. If it runs for a few seconds on starting fluid, then dies, it's the carb.
carbs, my tool of choice is electric
guitar strings. They come in lots of different sizes. When you buy a set, the set is specified by the smallest string in the set. A 008 set would have strings that start at 0.008" diameter & go up from there. A 011 set would start at 0.011" diameter. If you know the size of your jets, then you can choose a guitar string that is a close fit & guarantee that the jet is full open by passing the appropriate size string through it.
I have also found that 100LL grade aircraft fuel is great for cleaning
out carbs. The only thing is, if you run the engine on that stuff, be sure to change the oil
pretty darn soon. Standard oils get eaten up by aircraft fuel.
If the motor
does not start on starting fluid, then check your spark timing.
I'll assume that you have already checked to be sure that you have enough compression
of thumb is that 100psi is enough to run, despite what the book might say is actually correct or desirable. The farmer's test is to remove the spark plug, stick your thumb over the hole & see if the motor
blows your thumb off of the hole when you crank the motor over.
If all that looks good, then check to see if your exhaust
is plugged. That can stop a motor from running too.
The basics of any 4-stroke gas motor are: suck, squeeze, bang, blow. That is: air & fuel in, compress them, spark at the appropriate time, & exhaust
. All are required.