i have just put in a 402 in my truck 2wd short motor all new 10.75-1 comp 540 lift cam 750 vac sec 2800 stall 3.73 gears all msd ign my problem is this i loose all power at 4000 the motor pops out the exhaust and then at 4500 i have full power back also motor wont go past 5500 and it pops out of the carb at that point any suggestions i have switched every thing that i can think of ond back no change maybe bad valve springs any one please help not my first big block

You outrunning your fuel system? I'd slap a remote fuel pressure gague on it and make a run to see how your fuel pressure is holding up. You MUST be able to see the fuel pressure while you are driving. Fuel pressure readings at idle in the driveway are almost meaningless. If it's outrunning the fuel system it will be obvious- fuel pressure will nose-dive and then the motor will lay over and do things that sound similar to what you are describing.

ok thank you for your insight that was how i was leaning too will test soon and let you know also thare is a big debate on if my carb is too small most say yes but i think that its ok whats your take on the carb and also what to do with fuel delivery system truck lives on the street and i only have a stock fuel pump on it now once again Damon thank you

what about valve spring maybe a weak one or some thing like that i keep hearing that its a weak spring any thoughts

fuel is good any other suggestions im at a total loss would like to get the truck to perform good some day soon thanks for the help

I suggest going through the heads AND installing the springs that are supposed to be ran w/ that cam first!!

Stock, lo-po valve springs WON'T cut it!!

Period!!

pdq67