Octania

400+ CID
Advanced timing quite a bit, might be 15' BTDC with vacuum line connected at base of Edelbrock carb. Does not seem to change with removing vacuum hose even though VA unit has been tested to hold vacuum and both ports on the base of the carb read manifold vacuum at "idle"

My dwell/tach refused to read that day, so I had to guess the RPM at 800.

Engine would not idle down lower such that either of the carb ports would read 0 vacuum at idle. It would load up, struggle, and then die. Too much cam? I did not build the engine and do not have specs.

At this point I am leaning towards
retest the dist'r VA unit with the hand vacuum pump
leave the VA connected to carb or manifold since they are the same anyhow
live with the somewhat high idle, because what else can be done?

Does not appear to be any other vacuum leaks, new power brake booster is hooked up right.

Carb idle mixture adjustment screws appear to make no difference at all so they ended up around 2 turns out, assuming that if the idle circuit ever gets used, that will be at least "about right"

Removing the diagnostic vacuum gage from the large 3/8" nipple at the base of the carb results in a higher idle speed.

Idle vacuum is low [under 10] but pretty steady, comes up nicely when revved:

_http://www.youtube.com/watch?v=mALVWkeGn-k

remove the "_" before using the link above
it refuses to insert here as a link for some reason

seansolds

As long as you have total timing in at 34-36 and your primary timing set between 12-16. Your better off getting the tach to work, and do you have the edelbrock jet kit comes with metering spring sizes.. You may have to change them. You can find the manual at edelbrock online it will explain how it works to achieve the best idle and power. Once you changed the cam you changed the vacuum now the carb is going to respond differently.

garys 68&72

I would make sure your vacuum advance works first.
I've had better luck getting good idle with big cams using the manifold vacuum, even if it is low.

Run to Rund

Best would be to have vacuum advance disconnected and set centrifugal advance to 12 initial, 36 total. Then re-connect the vacuum advance. You may get around 25 deg. at idle with it connected.

CutlassDad

I hate "somewhere I've read" replies, but I have read that with a big cam and the resultant large opening of the primary throttle blades at a stable idle, the blades may be open enough to bypass the idle circuit completely.

Seff

If it's a Qjet, adding idle bypass air solves this problem.

cutlassefi

Since its an Edelbrock carb replace the step up springs with lighter ones so the metering rods don't pull out of the main jets. Try that first. Then if that doesn't work throw that carb away and get something worth a damn. If you haven't figured it out I'm not an Edelbrock carb fan, but try the step up springs anyway.

Thanks

buzzbomb

If everything is right on or close and you have to jack up the idle it can like you mention be bypassing the idle slots. A quick cure to this is drill a 1/8" hole in each of the front throttle blades and this lets you turn down the idle and get back into the idle circuit. This is an old holley trick and i do not see why it cannot be used on any carb.

Marx3

wow wow, if you timing is around 15 in idle WITH vacum advance applied, then your timing is way too low... What is the timing without vacum advance in idle? Btw, it might be better to use ported vacuum for a big cam and one fo the front ports in the bottom of the carb should be ported vacuum. I think you timing is low, making you have to set the idle screw too far in, to make the engine run ( causing the throttle to be open enough to uncover the ported vacuum source AND maybe cause nozzle drip on top of the already bad idle )
Below 10" hg sounds like a pretty big cam, but the low vacum reading is not necesarily because of a big cam... If timing is right and the carb's idle circuit is generous enough THEN it is a pretty big cam :-)