RX7Club.com - Mazda RX7 Forum - 1990gxl help questions (possible port problems and antifreeze question)

Well, I have a 1990GXL and when I bought it I was a bit too hasty and now I regret it, the guy who sold it to me seemed like a good person but ever since I've gotten it, i've had problem after problem, I've replaced the clutch, and the shifter bushings(no real help in slopiness), the brakes are going out, etc.

My main question is I took it to a dyno and in 4th gear it couldn't get over roughly 7k, and was sputtering after 6.5k, the top speed was 110MPH, does that sound right? i've been researching a bit and maybe it has to do with the 5th and 6th ports, I'm not sure if that's true or not, because I can get it to 8.5k in first and second gear(even though it struggles a bit after 7/7.5k, Is it possible the ports are getting stuck from time to time, also, whenever i rev it over 7k i get large puffs of black smoke coming out, and backfire. On the dyno it backfired like hell, when the guy let off in 4th after giving up on forcing it to higher rpm's there was a ton of smoke and the flame seemed like it was there for about 3 seconds before going out... they said it could be ignition problems but haven't sound a solid answer.

Also, I have a question about my antifreeze, after it was on the dyno i noticed it was leaking antifreeze, and the buzzer comes on every other day now so I have to top it off, I know if it's antifreeze getting combusted into the engine my engine is pretty much dead, but the thing is, my temperature is constantly in the middle and I realized that the buzzer will go off if i top the antifreeze off or even when the car gets warmed up, how likely is it that it's just a hole somewhere, or do you think i better be ready to give up on the engine?

Sorry sort of noobish questions, I searched around but wanted clarifications with my exact problems before jumping to conclusions and start working on stuff that I don't need to be messing up :P

Thanks