Honda accord -89 idle running problem

I´ve just bought a Honda accord lx 89 with a carburettor. When i´m driving
it really carefully it runs fine, but if drive it a bit harder so that the
engine gets really hot, then there´s no idle running any more. Instead of
850 rpm, it´s more like 200rpm. Then if i´m leave the engine running like
that for about 5 minutes, the idle running will go back to normal again.
Does anybody have any ideas what might be the problem. Sorry for the poor
language, i´m an uneducated Swede.

 

HOw long idle problem running last? If it last couple of seocnd, you don't
have to worry about as long as the car running fine.

 

The low idle lingers on for about five minutes, then slowly the idle goes
back to normal.If I then press the pedal to the floor once, the low idle
is back.This maybe indicates that there's something else than heatcaused.
It's like there's another port that opens when to accelerate quickly and
that port doesn't close again.