hesitationg after swap

[custom e30]

1988 bmw 325i convertible with a 2.5

i swapped out the bottom end with another bottom end from a 1986 325es, the bottom end is a 2.7 eta but i still have all the i parts including head,

ran great for 3 days and now is hesitating horribly, to the point where it will only run right if i have i full throuttle, otherwise its back fires like crazy and doesnt wanna go anywhere,

ideas?

[custom e30]

also it runs great when engine is completly cold and once it worms up, it instantly starts running like crap???

[jlevie]

The first steps would be to check for intake leaks and to check the fuel system

[custom e30]

did all that but i fixed, it, all i did was fill up the gas tank. yep thats right it had bad gas....