Please Help 50mm bbk wont start

[SlantEyedStoner]

I have some major confusion going on right now. I have a 50mm bbk installed on a 139qmb case. Everything has been upgraded with the bbk kit, cam, carb, head, cdi, etc.  The scoot ran great for a cpl months. A cpl weeks ago I went to start it and it wouldn't. I've gone over the entire system and motor and can't seem to figure it out. I have good compression, valves have been set and reset, carb w/ jets changed from 80-95, and cdi switched from performance to standard. I have good blue spark, good compression, and getting fuel to the carb. If I cover the carb intake, I get suction and fuel on my hand. I've gone through everything I can think of, and I'm totally dumbfounded over this. If I have spark, fuel, and compression, I should have a motor that runs, right??
Can anyone give me ANY logical suggestions to this? Thanks.

Here's what I'm working with:
139QMB w/ 50mm bbk,
50mm performance head w/ A9cam
racing CDI
performance open flow exhaust
Keihin Japan 20mm carb 
High flow air filter
new rectifier
new magneto

[stevec]

did you check the woodruff key for the flywheel? if it breaks your timing will be off.

[pledwar]

I'd definitely be checking my timing.. Stevec has a point it's possible it could be the woodruff key

[blaq]

Try new spark plug and manually choke it with your hand over intake

[SlantEyedStoner]

Yes, I've changed the spark plug, and Ive tried to manually choke it. When I manually choke it, it seems to want to start, but doesn't. However, it did start for abt 30secs. after playing with the choke for about 30 mins. then died. The woodruff key is fine and intack. And when I checked the valves and reset them, I made sure the cam and piston were TDC.

[katastroff]

A clean carb is a happy carb.

Have you cleaned yours lately?

[blaq]

What's size jet? U may have to upjet that was my issue and now she runs ez start up in this 20 & single digit wheather

[SlantEyedStoner]

I've changed carbs 3times with 3 different carbs that work and are clean. I've even tested them on my other scoot to make sure they were working as well. In fact all parts, cdi, coil, spark plugs, etc..have been tested on my other scoot just for reassurance. I've swapped jets and used 80, 85, 90,& 95. On my other scoot I have pretty much the same set up, 50cc bbk, A9 cam, etc.. except I have a Stroker crank installed on that one and have had no problems at all and it's been running strong for almost a year.
Thats what is boggling my mind. I'm thinking I should just pull the head and jug go ahead and inspect the entire top end, basically start from the beginning, inspecting it all. I really don't want to, but I will if needed. Unless there's any logical suggestions somebody can coe p with that I haven't tried already.

[blaq]

I meant main jet/pilot jet

[nightriderrv]

Have you done a compression test that tool can be your best friend and solve a lot mystery on these engines...

[nightriderrv]

Low comp could mean a bent valve, dirty valve, gasket leak....

[humanshield]

See my thread on this EXACT SAME topic

Mine wouldn't start either and everything was spot on.
Mine was that the chain tensioner was too tight.
All I did was remove it, reset it and VOILA! It has started every time since.

Worth a look.

Click Here

[niz76]

If it's acting like it wants to start when you're choking it- and sounds like you've checked and double checked everything else- maybe you have an air leak somewhere making it way too lean? Maybe cracked intake or something... Just an idea to maybe spark some other ideas...

[stevec]

sounds like too much air, i agree with niz on the cracked intake or it could be a bad spacer, cracked O ring on the intake or spacer.

[blaq]

If your still having problem change you pilot jet to bigger size that will also cause this problem