cold start miss on built ka

[struckinc]

i have a problem with my new engine build.. when started cold it idles ok but when you try to give it gas it has what feels like a miss.. i thought it was timing but timing is dead on 20 deg. idle is set at 775. it also has a brief pop through the intake when accel when cold. after it warms up it runs great..very strong. i changed the coolant sensor thinking it may be running too rich when cold but it didnt change anything. i have rechecked timing. no codes stored in system. now the engine is a ka bored 40 over, 10.5:1 pistons, port and polish head, no egr/emmissions, fuel pressure reg. set at 43 psi, walbro 255lph fp, intake ported, underdrive pulley, clutch fan removed, throttle body coolant lines removed, pacesetter header with 2.5" exhaust, stock cams for now, 170deg thermostat. this is driving me crazy so someone please help

[struckinc]

btw it is a 93 240sx

[rogoman]

Check for a vacuum leak with a vacuum gauge; the reading at idle should be around 18 - 20 InHg; at 3,000 rpm, it should be 21.

[struckinc]

the only vacuum lines on the car are for the brake booster and the fpr. the rest have vacuum plugs on them. and it only does it when its is cold...if it was a vacuum leak then it would doit it anytime i tried to accel right?