Suzuki RM 125 86' problem

I just rebuilded old RM, all engine parts are new. All is cleaned up and working.
Only one problem bothers me, i don't even know is it problem or its normal for old 125s.

Bike has really very very(even more) weak low and mid power. It almost stalls when you try to ride it. But than when you rev it goes on rear wheel with you holding on bike as hard as you can. I don't know did i do something wrong with valve assembly, jetting, spark plug, ignition i don't know but bike is not rideable. You ride it in high rpm range and than when it falls just a little bellow high it loses power and does bwaaaah. Is it normal old 125 or i did something wrong?

I don't ride the bike so often because i have newer much better and faster bike but i would like to have it done so i can take a spin sometimes.

Hey yesterday i noticed that bike smokes alot so i imediatly knew what was going on... seal screwed up.
I took engine apart and changed seals. I also reasembled and cleaned power valve and cleaned carb. Now the bike is running great! At least it got low-mid range back. Top hit is a little smoother and the bike is now great. I went to woods with friend on KTM 125 and i had no problems folowing him. Only on straights he kicks my ass.

Unfortunately here in Europe i can't get new plastic kit and other stuff that would make this bike look and go great. Now it just looks like graveyard...

I can get all plastics from Acerbis but only for 89'+ models...

My plastics are ****, 3 times amateur painted and all in diffrent color. I don't have radiator plastics and rear end is from newer CR, front mud guard is DIY...
I also need new pipe and silencer. Pipe is welded about 20 times by amateur, silencer is made from spray can. Also i can't find original brake pads but i know guy who repairs old ones. It's cheap and he can make you whatever you want.

I would like to rebuild the bike but we just don't have parts needed to do it well. I really like bikes with classic forks and they are great but i think i'll sell this one and finish my CR 125 woods bike project first.