Small Engine Question, HELP ASAP!

[MoparYoungGun]

I'm BAACK! Nobody probably remembers me or anything but anywho, I need help asap and figured this would be a great place to get it.

Ok, I race quarter midgets, basically it's a go-kart. I run a Honda GX120. The motor had been rebuild at the end of last season (around October of 2005) to Honda specs. The only mods done for racing is the stock fuel tank was removed and the whole air cleaner assembly was removed (only the carb remains). It has been running great, and I have been doin darn well thus far into the season. Now, all of a sudden it runs like crap. The idle has to be purdy high for it to stay running and it seems to jump around rpm wise alot at idle. Also, when reving it up and letting it decelerate it backfires more than it has in the past. And, it seems to spit a little gas out of the carb when running.

Firstly, could weak valve springs cause this? I would think that it could because when the motor completes the compression stroke it would blow out a little air threw the intake valve which could explain the little fuel blowing out and the pour idle due to it not getting fuel plus a little gas could be getting in the exhaust pipe due to the exhaust valve not closing all the way which could be the backfiring. Sorry if that was confusing but it's really hard to explain.

Secondly, what do you think it is? It is not the spark plug (Bosch Platinum +4 4477, just FYI), it's getting fuel and it is brand new (filled the tank an hour ago). It's not the kill switch. I don't know what else to try and I need it running good by Sunday which is when I'm racing. Please try and help me and please do it quick! Thanks!

Oh, and mods sorry if this is in the wrong place. Didn't know where else to put it. Thanks!

[MoparYoungGun]

[dodge freak]

Man how do I know ? I never even seen one of those motors. If you think its the springs change them, what does it have 2 or 4 valve springs?  Usually weak valve springs show up only at high rpms. I would guess its dirt in the carb. or a weak spark. You can change the springs with out pulling the head, I like the rope trick, thread a rope in the spark plug hole with the piston down a ways then turn the crank by hand till it won't turn any more. Now the rope is holding the valves up and you can change them. Might take 1/2 hour to do it, I change 16 like that a few times works great. Take gum out or brake cleaner too the carb. pull it off and open it up. If it still is not running any better get in to the spark unit. Hold on, guess you could have a hole in the piston or a bad valve, did you over rev. it ? Do a compression check, do you know what it was before ?