a buddy of mine has just finished a built low comp. swap into his crx runs fine but on the idle it fluctuates 300-400 rpm sometimesand will even dive down to sub 500 rpm the idle is set to stock was thinking it could be a timing issue or vacum issue just not sure o yea no turbo kit on yet and still in the break in process with aprox 200 miles motor done by justice race engines 255 lb walbro and runs consistent 30+ lbs. of fuel pressure but after you hit the gas its as if the engine is loading up insight would be most appreciated

 

o yea alot of carbon comes out of the exhaust enuff to where it leaves a trail but is a used tanabe

 

PUNCTUATION is youre friend. lots of carbon means youre running rich, but sounds like it could be a vacuum leak. bust out some carb cleaner and spray around see if you see any bubbling coming from anywhere