random question

[sidewaysFC]

just a random question way back in july when i was still trying to get my blue rx7 running and the new engine I had just put in had a lot of problems . I had just put a new water pump on it and I was testing to see if it was still over heating and it just started to have a fit it wouldnt stay running unless I had it at full throtle and even when it was at full throtle it would just kinda jump around any were from 1700 to 3000rpm the only thing I could think of that would couse that is a massive vacume leak but I cant see one just poping up like that .any who I gave up on it for the time being and just let it sit and bought my black rx7 but I plane on rebuilding my blue rx7 In june probably and i would like to know what would couse it to do that.