Hello Scotty " I have a 1983 toyota corolla wagon 1.6 rwd that I've replaced the original carburetor with 32/36 Webber.
My queston is what port on the spark advance diaphragm do I need to use going to the carburetor vacuum that only has vacuum when the throttle is moved ?
The 1983 corolla 1.6 had two vacuum ports on the spark advance diaphragm .
Any help would be appreciated.
Ronnie
Several ways this was done back in the day. Inside the distributor spark adv the ports should be the same location. One port will have a 1 way check valve, the other port will have another valve (bvsv) that opens based on its design (BVSV works by temp). This connects to the other port on the spark adv. then the out of these 2 valves are tee'd and connected to the on3 carb vac port.
Now here's what I would do (done many times in past). I would try different connections and plugs along with vac hose length while monitoring timing at several rpms (loaded would be ideal but not realistic) to achieve a timing curve I liked (try it, warm it up, run it on safe road and listen for knock during hard accel, repeat with different vac connections and timing adjustments to be a couple degrees shy of knock with normal gas you use. Also write down your values for comparison later.
However, if just a daily driver and not a project/performance play, I would connect as oem mentioned at top of my reply.
@hillbilly
Thanks for the info Hillbilly.
So your saying that each port on the distributor spark advance diaphragm are the same . Does this mean that either port will activate the advance mechanism?
Also what was the purpose of the two vacuum ports on the spark advance ?
Thank you for your time .
Ronnie
Does this mean that either port will activate the advance mechanism?
Yes, but need valving
Also what was the purpose of the two vacuum ports on the spark advance ?
Just a way to connect a check valve used to equalize pressures with baro changes between diaphragm and intake. The other valve opens when warmed up allowing timing advance (reving cold engine is bad so just in case, timing isn't advanced during this time to prevent cold knocks with advanced timing.
@hillbilly
Thank you so much for the well explained answer.
One more this i should mention is per the service manual is says to warm the engine to normal temp disconnect and block both vacuum hose. Adjust timing TO 5° , then whil idling replace the hose going to direct manifold vacuum and the engine should increase the idle which it does .
So just to be clear the port on the distributor diaphragm thats closest to the engine is always under full vacuum ( hot engine) at idle and zero under full Acceleration ?
Last question, do I really need a check valve on the full manifold vacuum going to the diaphragm port closest to the engine ?
I really respect your knowledge on this question and thank you so much for your help 🙏
Yes, full vac at idle warmed up everything working...max retard on the timing. WOT, least vacuum and the max advance on timing.,
The vac disconnect sets the static point of 5... this is purely mechanical timing reference point so under low vac (WOT) the mechanical timing can advance to it's mechanical limit (stop point). And at idle max vac to move the mechanical to max retard (mechanical stop.
Yea, Unless you start your car, let it warm completely (185) before you even touch the accelerator, in which case I would connect directly to manifold and plug the other port. Forget once in emergency and floor it and you could potentially break your engine (very doubtful but a bunch of ping/knock ain't good!)
In the 70's I would mess with the volume on the line by hose size/length. This dampens the response, i.e. move volume, slower timing advances (same advance in degrees but takes bit more time to get there). a couple hp difference depending other mods, etc. Purely a learning/education experience at the time as no real world value for regular drivers.
And thank you for the kind words, I try ; )
@hillbilly
Bingo " i think ive got it !
Timing set , ported vacuum from carb to just one port on the distributor and the other port plugged.
Car runs Great on the road " but idling the exhaust gases are very rich to a point it will burn your eyes standing behind the vehicle.
Any ideas on how to remedy this rich exhaust ?
As always thank you so much for the info. !
Carb jet change (what jet did you use when you installed it?). But first, check all induction to make sure no restrictions (air filter etc). You probably have that already taken care of tho. What's timing at when at idle with advance connected?
@hillbilly
Thank you for your answers !!!
Timing is at 5° . The carb jets are the original ones that were already installed at the Weber factory.
Now if I run a manifold vacuum to the port on the distributor that i have plugged off the timing will advance to about 10 -12 degrees.
Does this spark advance port need to be on full vacuum all the time , and do you think without this full vacuum that's causing the rich exhaust idle ?
I do apologize for all the questions but I'm so glad yoyr taking the time to educate me on this problem.
Again thank you so much.
Okay" if you were setting this up how would go about doing it .
Step By Step ?
Install with check valves vs. direct. And your gonna have to rejet that carb most likely as it has MANY applications an thus many jet sizes. The chances you got one just right for your application is simply statistical.
@hillbilly
Thank you Sir !
I have a couple of check valve that was on the original carburetor I can use on the manifold vacuum and I will purchase a jet kit from Red Line Weber . Also like you said it's trial and error to figure out the right combination.
As always thank you again !
YVW and keep enjoying : )