Carb. experts, have a 600 holly dp mech. sec. has been running good till today, will not idle with out dieing 2000rpm and above sounds and feels good, below 2000rpm its rough and poppy idle set at 1000 will stay there for about 20 seconds then slowly drop till it dies, smells rich idle screws don't seem to change anything, fuel pressure at about 7lbs. when it dies pressure drops to 0 right now, was thinking fuel pump at first, but leaning more towards carb. Could floats be stuck or way off or something like that.
. do you have an electric or manual pump? manual will go to zero when engine dies. if smells rich maybe the power valve is blown. did the engine backfire before it started running bad? holley tried to fix that prob but if it was a bad backfire it will get the power valve. had it happen to me on a brand new 750 its an easy fix and cheap. hope this helps im by no means a expert but that is what happened to me and i had similiar symptons also a float needle sticking could do same .. just have to check it all.
Check for vacuum leak at carb base/intake manifold.If all else fails you will have to pull the carb apart and look for debris in it. Could have a plugged up passage/air bleed...Good luck!!!
. yes check for vacumn leaks also , i reread ur post and saw where the air bleed needles had no effect, good sign of a vac leak.
Have a holly 110gph manual pump, if i take rpm up to 2000 or more and let up will idle at 1000 for about 20 seconds than slowly drop rpm till it stalls, can keep it running with pedal but will not smooth out till after 2000 or rpm also starts hard and smells real rich. Will check it out tomorrow have a car show at school in our town tomorrow, it's less than 1/2 mile from house should be able to make it out and back. Thanks for replys.
that really sounds like a blown power valve. you pretty much need to try changing it to see if its bad.
Restart it and tap on the top of the needle/seat screw with a big screw driver handle. Lots of times if there's trash in the needle/seat, this will dislodge it and the flooding condition will stop. You are running a fuel filter aren't you ?
power valve,trash in needle seats,defective/swollen needle seats-(ethanol blended fuel can cause this) are all possible common issues
Still have not got it right but better with a can of carb. cleaner, brother inlaws son is going to look at it sometime soon i hope.
