Hey guys my name is simon and I have a 74 Grabber 302. about 4 weeks ago I was driving it and is would sputter just a little bit but go away. when I start it it runs great for about 15 minutes or until it warms up then the carb begins to sputter and fuel will pop up out the top, you can put the pedal to the floor and it wont go over 15 MH. Thinking that the older holley 2100 2bbl had a float stuck or needed rebuilt I temporarily replaced it with an edelbrock intake and 600 cfm carb I already had handy. took it out yesterday and drove great then after 10 minutes or so when the engine warmed up, it started backfiring and spitting trickles of gas out of the top just like before. I have checked for vacuum leaks replaced rubber plugs on lines, I don't hear a leak, I'm at a loss on this. Any thoughts? looked under the car because it is a 74 and didn't see any cats on it. Thanks for any help guys.