What is a normal reading for a 289 with a mild cam at idle?
Idle speed is set at 650 rpm in drive.
I have a comp cams 256H
I am currently getting 14 in of Hg at idle in drive. is this too low. if so what is the best way to go about dignosing a vacuum leak?
Kip

 

no idea what it should be, but
a) adjusting ignition and carb (curb and mixture) will change vacuum.
b) to diagnose vacuum leak just spray some WD 40 around the base of carb, along the intake manifold gaskets
if idle changes (up or down) you have a leak where you're spraying.
If you have a powerbooster for brakes, check that hose as well.

 

funny you should mention the curb idle mixture I dont get much change by leaning it out or richening it.

also i have a holley 600cfm carb.

 

I've recently put the same cam in my 289 and am getting 15-16 @ 650,about the sameas yours. (I was getting 18-19 with the stock cam before the swap).

Does it seem to be running well?

 

okay, but it has a major hesitation off idle. it falls flat on its face then picks right up chirps the tires and hauls. it could also be a timing issue or a small accelerator nozzle. I just want to rule out vacuum leak first. also my mpgs suck, about 8-12 mpg. don't know if it is related but it might be timing.

 

also it runs much best just when it begins to warm up or on a cold day or night.

 

comp cams will tell you to set the timing @6 BTC. I've ended up setting mine @8 BTC staticand it gets a little more pep.
do you have an aluminum intake? if so you will need a spacer to keep the carb from getting too warm.
If it runs better cool maybe the carb is getting too hot ( if no spacer) or it runs better with the choke plate partially closed and when it opens ups you are too lean.

Initially, mine had a serious stall then would catch on. (sounds like the problem you describe) but I was able to "tune" it out.

my timing is set @8 BTC, curb idle @450-500, mixture screws @ 1 1/4 turns out from a light seat.

 

i have the same cam with a weiand action plus intake
vacuum is 15 hg
the timing is set at 12 bdc
anything lower than that and it runs rough.

the carb is a street avenger 570 with the mixture screws 2.5 out.
at 1.5 out the car wouldnt restart without pumping the throttle once.
2 out and it would restart but stumble for a few seconds.
2.5 out and it starts right back up.



no flat spot or bogging off the line however i have to put it in 1 to get the wheels to chirp.
it seems like it should have more power than it does

 

So does anybody think that 13 in of Hg at 650 is low enough to be a symptom of a problem or is it just on the lower side of normal. the engine only has 700 miles on it is it possible that the rings just havn't seated all the way yet or the engine is too tight. 10 mpgs is a lot lower than I was expecting. I was hoping for 15-17. passing time and Baxsom what kinfd of mileage are you getting?

 

I'd run about 8-12 initial, do you know what total timing is? 14-15hg should be about right for that cam, its probably the carb, check your plugs and see how they look, you probably need more pump shot. Frankly I dont like holleys......especially 600 # 1850's.