Vacuum Advance Or Not? - Moparts Forums

Register Log In Moparts Forums Moparts Question and Answer Vacuum Advance Or Not?

Print Thread

Vacuum Advance Or Not? #1405692 03/20/13 10:39 PM 03/20/13 10:39 PM
Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE RangerDan440 OP I Live Here
RangerDan440 OP I Live Here Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE	Mild 68 440, .509, etc Just rebuilt the carb and gave it a super tune and it had a slight hesitation when stomping on it. New power valve, clean jets, accelerator pump, etc. I normally dont run a vacuum advance, its always run better without but I decided to try it again and see if that cured the hesitation. It did, it revved smoothly and quickly but when I drove it, the timing was retarded enough so that it was noticeably down on power and pinging terribly when I put it on a load. ???

Re: Vacuum Advance Or Not? [Re: RangerDan440] #1405693 03/20/13 10:54 PM 03/20/13 10:54 PM
Joined: Jan 2003 Posts: 12,074 Benton, IL. D DaveRS23 Special needs idiot
DaveRS23 Special needs idiot D Joined: Jan 2003 Posts: 12,074 Benton, IL.	What is the correlation between hooking up the vacuum advance and the retarded timing? Did you mean over advanced? Was the hesitation there before you tore the carb down? Or did it appear afterward? Master, again and still

Re: Vacuum Advance Or Not? [Re: DaveRS23] #1405694 03/20/13 11:01 PM 03/20/13 11:01 PM
Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE RangerDan440 OP I Live Here
RangerDan440 OP I Live Here Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE	oops, yeah I meant to say with the Vac Adv hooked up that it was too far advanced that it ran terrible. And no, before the rebuild I didnt have the hesitation problem, it ran great. The reason for the rebuild was the old gas tank was rusting from the inside and there was rust all in the filter and carb so I R&R'd the entire fuel system from the tank forward.

Re: Vacuum Advance Or Not? [Re: RangerDan440] #1405695 03/20/13 11:12 PM 03/20/13 11:12 PM
Joined: Jan 2004 Posts: 1,250 North Carolina 4 469runner pro stock
469runner pro stock 4 Joined: Jan 2004 Posts: 1,250 North Carolina	The timing should be set with the vacuum advance disconnected. For that combo. about 38o at full advance, 2200-2500 rpm (centrifical and static). Then hook the vacuum up, this will probably take the advance to 52o or so, probably too much. If it is knocking under light load then the vacuum advance can be dialed out a few degrees at a time until knock disappears.

Re: Vacuum Advance Or Not? [Re: 469runner] #1405696 03/20/13 11:18 PM 03/20/13 11:18 PM
Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE RangerDan440 OP I Live Here
RangerDan440 OP I Live Here Joined: Jan 2003 Posts: 12,861 Gloucester,VA STOP MOVING HERE	so did too much timing cause the hesitation before I hooked up the vacuum advance?

Re: Vacuum Advance Or Not? [Re: RangerDan440] #1405697 03/20/13 11:38 PM 03/20/13 11:38 PM
Joined: Jan 2003 Posts: 75,005 U.S.S.A. JohnRR I Win
JohnRR I Win Joined: Jan 2003 Posts: 75,005 U.S.S.A.	Quote: so did too much timing cause the hesitation before I hooked up the vacuum advance? what is your initial and your total advance without the vac advance hooked up ? what distributor are you running ?

Re: Vacuum Advance Or Not? [Re: RangerDan440] #1405698 03/21/13 12:48 AM 03/21/13 12:48 AM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	Quote: And no, before the rebuild I didnt have the hesitation problem, it ran great. If nothing was altered but the carb I would start back there for the hesitation cause. For the timing I would set the initial with the "vacuum gauge method" starting with 15BTDC then shorten the slots to get 36-38 (depends on octane/quench) then play with springs & toss the heavy spring with the elongated loop on one end & sub in a mr gasket or MP light spring & keep the OE light spring for a starting combo & staying just under the pinging point at WOT up thru the gears on your hottest/driest day then hookup the vac adv & solder strips of feeler gauges on the back side to limit the notched arms' travel into the pod staying just under the pinging point at a steady interstate cruise (high vacuum) speed at an RPM at or above the point where the mech slots are maxed out (full advance) then in everyday driving stay just under the pinging point & adj with a 3/32" allen wrench in the pod nipple & CCW slows the onset of the curve. Alot of work but ALOT of gain to be had. Must be done IN ORDER. Note that vacuum advance will alter rotor phasing & can contribute to misfiring if the rotor tip gets far enough away from the underside of the metal cap terminal. NAPA offers an Echlin MO3000 rotor that has an .060" longer blade for $8 & change out the door & there's several ways to alter rotor phasing. Drill a 1/2" hole in the top flat of your dist cap 2/3 of the way between the center terminal and the #1 terminal & freeze the rotor by shining your timing light straight down in there when running & note that ONLY the vac adv (from eng load change) changes rotor phasing position. live every 24 hour block of time like it's your last day on earth

Re: Vacuum Advance Or Not? [Re: RangerDan440] #1405699 03/21/13 12:55 AM 03/21/13 12:55 AM
Joined: Mar 2007 Posts: 3,277 West Coast, USA jbc426 master
jbc426 master Joined: Mar 2007 Posts: 3,277 West Coast, USA	Are you running it to manifold or ported vacuum? 1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)

Moderated by Al_Alguire, Hotwheelsjr, moparts, not_a_charger, RangerDan440, tboomer

Hop To

Powered by UBB.threads™ PHP Forum Software 7.7.1