timed vacuum vs manifold vacuum

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65Vart

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Stupid question #50 . I have always run my 273 (mopar electronic conversion kit with eddy 600 carb) using the "timed vacuum" port on the passanger side of the carb. Ive noticed the ignition seems to break up at higher rpm. Should I be using the other port on the carb for manifold vacuum? (driver side).
 
This question will open up a can of worms here....LOL. But if your breaking up at high r's under wide open throttle, there's no vacuum to the advance can either way, so that's not causing your issue.
 
So being a fairly mild street motor is timed advance the way to go? Im just trying to rule some things out.
 
So being a fairly mild street motor is timed advance the way to go? Im just trying to rule some things out.

If that's what you've used successfully in the past with your timing and advance curve, I have to think there's another issue in the ignition system. What rpm's does it seem to start acting up? If it's in the very high r's, say 5000/6000, it could be the valve springs getting weak. I'm not ready to go there yet, but if you can give a more detailed description of what's happening, wide open throttle? and the rpm range, that will help with the diagnosis.
 
Its up there 5000+. Engine still wants to pull. The ignition system is new put there by me (orange box kit). The cam and springs were not done by me so maybe the springs are tired. That is something to think about for sure. Its a mild solid 20-246-4 Comp cams .468 lift. I know the springs were for the kit. Looks like its not a simple fix.
 
Fuel delivery?

Only real difference between the two vacuum sources is one will show signal at idle, the other should not. Once you crack the throttle, they should mirror each other.

There shouldn't be enough vacuum at full throttle to activate the advance pod.
 
Oldmanrick is right. At high rpm or full throttle run there is no vacuum and therefor no added advance from the vacuum canister. It doesn't matter whether it is plugged into the ported or full manifold side of the carb.

The only difference between the two is that the manifold side adds timing at idle where the ported side only starts adding timing once the throttle blades open. So the breaking up on high RPM must be coming from something else.

In my opinion, if you are running a street car using vacuum advance is a must and the ported side is the way to go. The only benefit of running the vacuum advance on the full manifold side of the carb is if you are running a high-duration cam.
 
I checked the specs and that's not a large cam at all. They recommend 901's, a single spring, but even fresh stock spring should not cause a float issue. I'm no dist/ignition expert at all, other then I know adv. curves, i'm from the point dizzy days, but I still think it could be ign related? See what kind of post's you get for a while. Might be someone with the same issue that can help.
 
Is the orange box grounded REALLY well? Got any spare boxes you can try?
 
Did you have the same problem before you put in the new electronic ignition you mentioned?

Do you have a fuel pressure gauge installed? You might be seeing a huge fuel pressure drop at high rpm causing the bowls to be drained due to the reduced flow. Have you checked your carb's float levels to make sure they are within spec?
 
Is the orange box grounded REALLY well? Got any spare boxes you can try?

^^^^^ This!

I've seen inconsistant results with the Mopar orange box. A friend of mine had one on a closed chamber 318 in his '67 Fury and it started feeling for a ground, internally, like a bad spark plug wire on a header from burning.

Eventually, it started acting like a capacitor and buzzing, trashing the entire electrical system to a point where it stressed the ammeter lead to the point of burning.

We traced the short back to the orange box.

I'm not convinced that those computers are doing what they should be doing, all the time.

There is a company that is making a replacement computer with a tunable limiter dial on it. It's completely digital and likely does a better job at keeping timing together.

http://www.thertgarage.com/products.html

I'd like to see some reviews on it, but it seems like a good idea.
 
Did you have the same problem before you put in the new electronic ignition you mentioned?

Do you have a fuel pressure gauge installed? You might be seeing a huge fuel pressure drop at high rpm causing the bowls to be drained due to the reduced flow. Have you checked your carb's float levels to make sure they are within spec?
car ran like crap with the old points dist and I couldn't adjust it so I just changed it to electronic.
 
^^^^^ This!

I've seen inconsistant results with the Mopar orange box. A friend of mine had one on a closed chamber 318 in his '67 Fury and it started feeling for a ground, internally, like a bad spark plug wire on a header from burning.

Eventually, it started acting like a capacitor and buzzing, trashing the entire electrical system to a point where it stressed the ammeter lead to the point of burning.

We traced the short back to the orange box.

I'm not convinced that those computers are doing what they should be doing, all the time.

There is a company that is making a replacement computer with a tunable limiter dial on it. It's completely digital and likely does a better job at keeping timing together.

http://www.thertgarage.com/products.html

I'd like to see some reviews on it, but it seems like a good idea.
that looks like a cool piece, anyone running one?
 
Also on that website they talk about how unreliable the orange box is and that they have done test showig the box to be inaccurate about 5k rpm. I want to also the orange box can retard timing quite a bit after 5k
 
your coil may be falling off in the secondary causing ignition breakup, try swapping it out with another coil. (coil with external resister)
 
that looks like a cool piece, anyone running one?

I'm going to.

I've actually strayed away from running a Mopar Performance ECU because of the advance problems and grounding problems I've experienced with helping friends work on their systems.

I've thought about running an MSD, I LOVED the original Jacob's Electronics Pro Street and Ultra Coil systems, but the Mr.Gasket units aren't like them anymore. For the money, even though it's physically compared to a Mopar ECU, it does a lot more and is easier to run than all of them.

I think this system, combined with a good coil, blueprinted dist/cap, good wires and plugs will help quite a bit.

I really think this car has an ECU prob.
 
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