Re: Low Manifold Vacuum
1st some questions:
What are cam specs?
You said you cant remember cam specs well look them up or find cam card because we need that cam info so wek now approx what idle/low engine speed vacuum should be along with motor size is too which you also didnt include.
What size motor?
What is base timing set at & at what idle rpm?
What is total timing & at what rpm is it all in?
Doesnt have to be vac leak as stated abve with low int vacuum.
If base timing is overly retarded with perf cam that alone will make idle /low engine speed intake vacuum considerably lower then it should be.
Ensure you have approx 18 deg base timing with perf cam & vac adv hooked to fullintake vac all the time.
Set base timig with idle at approx 600 rpm to ensure mech adv isnt partially activated at idle upsetting base timing adj.
Look for approx 36-38 deg total timing in by approx 2600-2800rpms,but the already suggested 4k rpm is way to late/lazy for total to be comming in IMHO.
BTW,in general cam profile-size-duaration etc vs motor size has a large affect on idle/low engine speed vacuum along with if base with perf cam is too retarded too so keep that in mind when dealing with issues like this.
Now if you ensure base/total timing are correct and if running vac adv to full ntake vac if running one along with idle mixture/idle speed set correctly and idle vac is still low for cam vs motor size then look for poss carb/intake/ vacuum leake/s at that point but enusre base /total timing is right 1st with vac adv to full int vacuum for most street perf motor's unless its real hot without enough vac at idle to run vac adv.
1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)
2009 HD ELECTRAGLIDE CLASSIC ULTRA (GOT 11/14 W-9,700 miles)