Ok so I'm currently running the 123ignition dist on my 2056 with dual webers. I read the instructions and don't understand the mapping. I also don't know how it all works together. Can someone educate me on the vacuum adv and what curve would be best? As the rpm's increase it creates more vacuum thus creating more adv, but if I already have a curve setup to go from 12 degrees at idle to 28 degrees at 3000+ will the vacuum adv move the timing even higher once it is hooked up and mapped?
On dual weber's you shouldn't run vacuum advance, dual carbs (or ITB's) have a piss poor vacuum signal and will likely only cause you headaches.
The more duration the cam has the worse it gets.
If you really want vacuum advance I would run the vacuum hoses to a central sealed box then to the dizzy. I'd also stick a .023 mig welder tip into the vacuum hose(s) to help even out the pulses.
Likely you'll have to tap the manifolds in a couple of different places and play around to find the best vacuum signal.
I won't be surprised if you end up capping/disabling the vacuum advance.
I'm not sure why Webers shouldn't use vacuum when they come from the factory with vacuum ports.
If I am going to use it I will only be using the vacuum port on cylinder 4 (off the carb) with an anti-pulse valve.
I'm getting the info from John of ACN.
Currently the carbs vac port is capped, but the dist is open (McMark - Never cap the vac port on a distributor)
Isn't there a 123 that doesn't require a vac signal?
To echo what Mark said, after running the 123ignition on my 2056, the vacuum advance is not necessary.
Look at the literature that shows the vacuum advance start, vacuum end, and degrees the vacuum is effective only over a short range and it is quickly overtaken by the programed advance.
As shown in the original Bosch dizzy information (note this is a representation of the curves and the values have to be doubled to read correctly) shows that at 3500 RPM you get a total of 22 degrees advance which matches the 123 numbers. Yes I know that you are thinking at 3500 rpm advance should be at 27 degree. True but the engine is not designed to fire at TDC so there are about 5 degrees to account for that fact.
Looking at the dashed line for vacuum advance it shows that the vacuum is not additive meaning it will never advance above the 22 degrees due to vacuum. It only helps the change occur faster.
On my 2056, I used the negative advance because as with the stock engine, with the timing set to give you 27 degrees at 3500 rpm it results in more timing at idle which will give you more RPM. The higher timing at idle gives you more RPM than the 900 you want so you can take some of that out using the negative vacuum settings if needed.
Using curve B allowed me to adjust the idle into the perfect range. You may or may not need to play with the negative vacuum depending on you idle adjustment.
So Mike, I will be installing mine soon, right after I get motor back in the car and have it running. Once I do that I will put this in, I just don't want too many variables at once, - but to clarify, when you had the d-jet stuff on your motor you ran which curve setting on the 123 dizzy?
ok that is where I will start. My idle was about 1000 before, so if its a bit more than 900 no big deal,
so now that we have eliminated the old trigger points, how about a more modern solution to the MPS??( I guess that would be a custom digital injection system like megasquirt or the like) just seems like there ought to be a way......
The whole reason behind the want to use vacuum adv with the standard curve on the 123 is due to my webers having a lean hole. John from aircooled.net seems to think if I have more advance at light throttle (transition between idle and main circuit) then it wont lean out. I have several different jets and have tried several different combinations to fix this lean hole. The best one has been setting the idle to a 55, but then I'm running real rich. Also it only allows for a 1/4 turn out on the mixture screw for highest idle. If I have more advance during the transition it should help with the "leaning out" Correct me if I'm wrong here.
I am not using any vacuum on my 123
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