Motorcycle Repair: Yamaha PW-80 wont start, yamaha pw 80, clymer manual

Question
Hi,

My sons Yamaha PW-80 2-stroke dirt bike was running okay, but I'm in the habit taking the carb apart and giving it a good cleaning a couple times a year. So I did it this spring and couldn't get it running right. It had an air leak somewhere. Probably around where the carb goes onto the manifold. I know this because I had the same problem last year and brought it to the shop and they siliconed it. I tried gouping it myself and it didn't work. It even got worse, after taking the carb off about five times it wouldn't even try to start. There's a round plastic sleeve that goes around the intake and it was worn. Anyway, I got frustrated with it and ordered a whole new carb. It came with the new sleeve and I put it on the bike. I thought to myself, finally! I will have this headache behind me. Well I tried firing up the dam thing and it still won't even try to start. I see as I'm kick starting it, gas is flowing out the overflow tube. I was doing this with the old carb at the end as well. I'm getting a spark, so what else do you think could be wrong?
  
Thanks,
Mark


Answer
Mark,
 New carbs don't always come adjusted.  You need to check some critical points before putting it into service.  If you don't have a Haynes or Clymer manual I highly reccomend purchasing one now.  In it it will give you the dimension on which to set your float hight.  Once you've done that you need to check that the needle valve is not stuck as well as seating properly.  If not you will have a large amount of fuel pouring out of the overflow tubes like you describe.  This can cause the bike to flood and temporaraly foul your plug.  Be sure your reed valves are not fused/stuck shut and are plyable/flexible.  You should not need to seal the carb boot with much of anything if it is flexble and not cracked.  If it is worn get a new one and sufficiently tighten the clamp.  If the bike is running ok no need to dissasemble carb.  Install an inline fuel filter screen from your local shop for a couple of bucks and this will ensure you are not getting any foreign debris into the carb.  Always drain the carb before storage and flush w/ gas line antifreeze.
 If the bike has been running ok and is not overheating or revving high at idle w/ fluctuations your crankseals should be ok but if you have experienced this you could be drawing in air from the crank seals and leaning your mixture w/o any fault from the carb.  Typically this does not make the engine hard to start though.  Check those carb settings and NEVER use anything but compressed air and solvents to clean out jets and airways.  Picks or wires can seriously damage the precise venturi action that takes place to properly atomize fuel.  If the jets are damaged you can have running problems.

Hope this helps,
Mike