stumbling 200 at idle

[Anonymous]

long story here.
67 mustang, stumbles at idle.
rebuilt carter YF carb. replaced throttle shaft bushings, eliminated any source for vacuum leaks, 12 degs timing, 30 degs dwell, new fuel pump, new fuel filter, 170 psi compression check all cylinders. running 89 octane pump gas. new coil, cap and rotor. had pertronix on it now points, same problem.
timing chain replaced 3 years ago. head rebuilt in 95.
seems to run fine cold, warms and starts stumbling like a vacuum leak.
vac gauge reads about 13 inches then when hot stumbles back down to 9.
and ryhmically goes up and down.
no fuel boost at idle. seems carb functions properly.
cracked intake? cracked exhaust manifold?
where else should i look?

thanks

 

[bigcatchdaniel555]

have you done a compression test a low comp. ration or a blown gasket may cause a stumble

 

[JackFish]

Perhaps the carb needs to be checked out. Did you rebuild it yourself?

 

[Anonymous]

170 comp. all cylinders.
i rebuilt the carb myself with the Niehoff brand parts.
they suck. needle and seat didnt work properly and it flooded.
mechanic rebuilt the unit with Borg Warner kit. no more problems with carb.
he is now double checking that the sufaces (carb base to linkage and intake are in fact flat) to rule out a vacuum leak.
seems to be most noticeable at operating temps.
like something is expanding and letting air in.

thanks for the input.