A mate of mine asked me to have a wee look at his s2 that he has built. Said it was starting and running fine, he never drove it. I never seen it running. When I went to look at it, it wasn't starting, not even trying, changed plugs, got it to try, but will only start if you hold the metering head flap open a small amount, if you let it go, it cuts out. If you try & rev it, you have to manually open the flap for it to rev. Any ideas please?