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63 Posts
Guys, bear with me... I have just got my car from the shop and have done about a 1000 miles with smiles. The car is a 69 396 SS with a 454BB and a new 750cfm performance Holley (one metering block and electric choke and vac secondaries).
It has a mildly sporty cam Comp Cams 230 duration and .520 lift, nothing hairy
Weiand intake
781 Heads
2.19 intake 1.88 exhaust
3/8 pushrods with guides
roller rockers
2800 stall
It WAS running really smoothly idling at 650/700rpm and pulled cleanly... no complaints whatsoever.
Suddenly the idling is lumpy as hell.. if I can get it to idle at all, the car won't run smooth and it dies off the throttle. Now it also takes a while of stirring and farting to start and it used to start really easily.
So... what should I suspect? surely the idle screws can't just loosen off?
The carb is new... the gas tank is not... The choke comes off a bit sharpish but the crappy idle now happens cold or nice and warm.
I can only think of two things... that would change so suddenly (unless I've lost spark on a cylinder or two.. but I can't think that is the case, as those bits are new).
(i) Crap in the idle pathway
(ii) A vacuum leak
So...
(i) How do I test for crap in the idle gubbins?... (vacuum gauge and twiddle with the idle screws at lowest possible stable idle? It may be off the stops at that rpm)
(ii) How do I test for a base vacuum leak, how much of a leak screws things up? (I can plug off all ports and check the tubes).
Any help from you guys really appreciated, I don't want to take it to the shop.
It has a mildly sporty cam Comp Cams 230 duration and .520 lift, nothing hairy
Weiand intake
781 Heads
2.19 intake 1.88 exhaust
3/8 pushrods with guides
roller rockers
2800 stall
It WAS running really smoothly idling at 650/700rpm and pulled cleanly... no complaints whatsoever.
Suddenly the idling is lumpy as hell.. if I can get it to idle at all, the car won't run smooth and it dies off the throttle. Now it also takes a while of stirring and farting to start and it used to start really easily.
So... what should I suspect? surely the idle screws can't just loosen off?
The carb is new... the gas tank is not... The choke comes off a bit sharpish but the crappy idle now happens cold or nice and warm.
I can only think of two things... that would change so suddenly (unless I've lost spark on a cylinder or two.. but I can't think that is the case, as those bits are new).
(i) Crap in the idle pathway
(ii) A vacuum leak
So...
(i) How do I test for crap in the idle gubbins?... (vacuum gauge and twiddle with the idle screws at lowest possible stable idle? It may be off the stops at that rpm)
(ii) How do I test for a base vacuum leak, how much of a leak screws things up? (I can plug off all ports and check the tubes).
Any help from you guys really appreciated, I don't want to take it to the shop.
