1985 nissan 4x4 missing at 2500 rpm

[nateman1974]

Hello, I just bought an old beater for 400 bucks and the problem I have is that at 2500 rpm in any gear it spits and sputters and looses power. Now if you engage the clutch at this point the engine will rev up all the way but when you disengage it it is spitting and sputtering again once it hits 2500 rpm. I have replaced the plugs and fuel filter to start with but it didnt help. any ideas? It has the 4 cylinder with 8 plugs. all new to me. Thanks