If you don't have a 12 Volt starter, then I sugget you get one of those.....I once didn't have one, and it took forever for me to crank my engine for the FIRST time ever!!

Once I got the starter, I just put it up to the nose cone (spinner) and started spinning, and eventually it will start, now always......

Also, check to see if all your head screws are tight.....I had the same problem and my engine wouldn't start because I didn't have enought pressure or whatever because my head screws (for the engine, not my head!!) were loose, and I didn't have a tight seal...

Hope this helps...

I'm sure alot of others will come and help too......

BTW, What type engine is it??