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So my idle advance system is not working, I've got a new distributor, and I've tested the advance diaphragm by removing dizzy cap and applying vacuum, it held. I've also recently taken apart the carb and cleaned everything out. Still the timing mark will sit at 5° whether the lines connected or not. Any ideas guys? Here's pictures of what I'm talking about: Emissions set up Idle advance system I'm pointing at where the idle advance line connects to carb, what I believe is the fuel cut port, right below the (blocked off) fuel cut solenoid, and just to the right of idle advance screw. Does this look right to everyone?
the best thing to do is forget getting idle advance from the carb, and pull it straight from the manifold. Are there any vacuum ports available on teh intake manifold, i think i can see 2 caped off wiht black vacuum caps in ur photo.
Get out your vacuum gauge and see if there is vacuum at that port at idle. That small black cap on the carb is not present on a genuine Canadian carburetor. What you've done appears to be correct. If the throttle plate has uncovered this port you will not have vacuum on it, so try slowing the idle down, or resetting the idle speed/mixture it as per the Canadian carb directions. If you take the vacuum for this sub-advance port right off the manifold you will have too much advance at idle. You can take the vacuum signal for the main diaphragm off the manifold and then completely disconnect the sub diaphragm from a vacuum source.
We also seem to be talking about just one of the advance ports on your distributor and I think it helps to have them both connected. One draws from the carburetor and the other from the manifold vacuum.
With the truck running and the hose disconnected from the carburetor, can you hear that port drawing vacuum? Like a whistle? Does it change if you cover it with your finger?
Hey everyone thank you for your replys, here's a couple more questions/answers. There is a low whistle at the fuel cut port for idle advance, but I suspect it's not enough vacuum for some reason. Yesterday it looked like advance was maybe jumping one or two degrees at idle but definitely not seven.
As of right now I've got the idle advance disconnected and plugged on both ends, I set timing to 12° and the truck runs fine. Does this sound alright to you all? I think what concerns me is will this advance my total timing by 7° because it's starting at 12 not 5? Like I mentioned, there's no ping, maybe I'm just overthinking it.
I'd like to understand this a little better, are you guys suggesting I move the timing advance line to the manifold port? And put the idle advance where that line is. The timing advance currently works well, the mark will jump up under acceleration.
the vacuum advance sub diaphragm should get its vacuum from a port with strong vacuum at idle. so, the diaphragm closest to the distributor body should be connected to the manifold as close to the carb as possible.
Last edited by Thommo Thompson; 03-21-2018 at 01:05 AM.
The sub advance only works at idle, the sub advance diaphragm is the one closest to the distributor. It should give if I recall right about 7 degrees of advance at idle only except if you have HAC then it will give this advance all the time over about 4500' above sea level. The main advance diaphragm is the furthest one away from the distributor. Again if I recall it will give either 12 or 15 degrees. Both advance lines are off the carburetor. If you put that line on the manifold with the sub still connected you may end up with too much advance at and off idle.
Inside the carburetor there are two ports for this, one is above the throttle plate for the main advance (at idle and 'sees' no vacuum) and one is below for the sub advance (again at idle and 'sees' manifold vacuum). These ports are on opposite sides of the primary barrel, you may be able to see them if you open the throttle wide and look in. When you open the throttle, the throttle plate 'moves' the sub advance port from vacuum to atmospheric pressure and therefore no more advance is realized from the sub advance. Conversely the main advance port now goes from atmosphere to vacuum and starts supplying advance. There may be a blend in period where both are supping advance and this may explain why you will get a bit of light throttle ping that goes away if you open the throttle a bit more. Study the diagrams in the FSM and you'll get what I am saying here.
Understanding this is explains why its a bad idea to move the main advance right to the manifold with the sub advance still connected.
Again...if you want to run the main advance off the manifold you should disconnect the sub entirely.
Again...get your vacuum gauge and connect it to the ports on the carb, the sub advance port should have about 22-24"Hg at sea level.( the needle may be a bit unsteady, which I think is due to the pulsations of a 4 cylinder engine, but thats another topic) It may vary due to altitude (-1"Hg per 1000'). If it has significantly less the passage or port is plugged, likely with varnish or read on. The main advance port should be 0"Hg or close to it. If there is vacuum on this main advance port the throttle is open to far. So...I cant see if you have an idle mixture adjustment screw (I know its capped off so you cant play with it on some models) So if you're compensating for weak idle mixture by increasing the idle speed you may be exposing that sub advance port partially or fully to atmosphere. If you can, adjust the idle with the lean drop method explained in the FSM. I assume you have a vacuum gauge cause you seem to indicate you have a vacuum pump and most newer ones have a gauge you can use for testing
12 degrees of initial advance may or may not be too much. If its not pinging anytime then no. Many factors effect this. Altitude allows usually 1 degree more per 1000' extra elevation (i.e. at 4000' you can add 4 degrees) If your timing chain is old it could be stretched a bit which has the effect of retarding both cam and distributor timing which would allow you to advance the ignition timing to compensate for the stretch without ping. As an example before I replaced my chain I could run 10 degrees advance with 87 octane at 1500' above sea level...and the truck would run like a deer. (it had better top end but worse low end...but that's a whole different subject) Now with a new chain I can only run about 6-7 before I get that light throttle ping. (I actually run about 8-9 degrees cause I use 89 octane, more to get gasoline with < 5% ethanol content)
The million dollar question is why Toyota has the two advance diaphragms. From reading the FSM I can only guess that it has something to do with emissions and/or the HAC system.
Disconnecting the main advance system will not do any harm except your less then WOT fuel economy may suck...but its a 22R so most of the time its on the boards anyway!
Some of this may sound apocalyptic but if its working O/K for you don't mess with it!
Last edited by Old83@pincher; 03-29-2018 at 08:31 AM.
03-19-2018, 02:42 PM
