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Fixed my high idle with dual Webers and dual point dizzy.


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      Thanks to this site and all of you knowledgeable people. You have solved many of my questions before I even had to ask them. 


     I have a 72 510 that still has a stripped down L16 in it with dual Weber 42s. Yes, 42's are a bit large for an L16 and EI would be better than points. But I'm trying to work with what I've got for now. No emissions bs or anything else extraneous. Just the motor and trans. I did a full rebuild on the motor, swapped in a short tail 5 spd, and rebuilt the dual point distributor and both carbs. After a bit too much time guessing and tuning, I sprung for a wideband AEM gauge which made things much easier. I was able to get both the carbs and timing right, but I still had a high idle. 1350 rpm.


   Okay, so this was a test thing to see what y'all thought about it. Since webers like a bit more timing than stock and also the old 42's (and 40's I think) don't provide for a vacuum advance, I had higher than normal initial timing. To solve this, I made creative use of my dual point distributor. I wired the second (retarded) point to a micro switch that only was on at throttle closed. This way, any time that the throttle is open, it runs off of the primary (advanced) point with an initial timing of about 14*. That's where the motor is happy up top at about 39*. I think that's a touch high, but no pinging or over heating occurs. Plugs and the O2 sensor look great 4000+. Idling on the primary point gave me an idle of about 1350 rpm. Not horrible, but not good. With the throttle closed, the switch activated, and the secondary point retarded 4* from the primary, it gives me an idle of 900ish. Much better. I was also able to re-tune for a bit more economy down low rpm.


    I searched and searched but could not find any other threads about this specifically. I apologize if I did not see another post about it. If there is anything I am am doing wrong missing, let me know. 


    I have a few pics having trouble putting them in. I will figure it out and put them in later.



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Hi Ryan, welcome to Ratsun.


All gas engines since the late 60s have carbs and distributors that have zero vacuum advance at idle. This is strictly for reducing emissions, period. The vacuum is no longer directly from the intake but from a port just above the throttle plate. Here, at idle, it senses atmospheric pressure, but as the throttle lifts to and above the port, intake vacuum is applied. That said, ALL engines today crave more advance at idle because this is where they would normally run best but are constrained by today's ported vacuum carbs.They would idle smoother, stronger and cooler. I'm guessing you have intake vacuum advance and why the idle was so high.Timing at 14 degrees is why you have 39 degrees total at full throttle above 3,500 RPMs. Initial + mechanical = total advance.


Your use of the dual points is very innovative however retarding the timing to set the idle speed while great for emission isn't the best for good idling characteristics. Total advance should be closer to 34/36 degrees for a L series. Maybe limit the mechanical advance slightly by blocking the advance weight's travel. You can still run 14 degrees advance and just turn the idle speed down. Without the retarded idle it will run where it runs the strongest, smoothest and coolest.

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Thanks for your advice. I never had any vacuum advance. ported or manifold. I set the timing to 39 total and let the initial timing fall where it wanted. The motor just really likes it that high. The carbs are set just about as low as they can be. The plates are fully closed, and while idling, the mixture is about 13:1. I can bring the idle down with the mixture screws while only running the primary point, but it idles suuuper rich. If I take the idle down to about 1000 rpm with the mixture screws, it idles at less than 10:1 and just smells to high heaven like unburnt fuel. I'm not exactly worried about economy and definitely not about emissions, but it is so simple and it saves fuel at idle and keeps my car from smelling like it is running rich as hell. Plus it runs exactly the same. Idle is just as smooth, just a bit lower. Power is not effected since the second I touch the throttle, it shuts off the second point and everything goes back to how it was. 


I don't know, I'm just playing around and trying to learn something. 

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Adjusting the idle mixture and retarding the ignition is not the way to set the idle speed. Idle speed should be around 650-750. If you can't adjust the mixture to get around 15 then the idle circuit is set up for a larger engine.


Idle should be 14.7 or stociometric. 13 is unnecessarily rich. Hard wide open throttle is usually 12-13. If super rich at idle then the carb jets or idle circuit is set wrong for the engine size you have. (44s on a 1.6 Liter?)  Lean it out and likely the idle will drop without the need for the retard set. Don't know much about these carbs but the chokes are replaceable with smaller ones? Someone?

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They are 42s and chokes are available in a number of sizes, if you can find them, but they have nothing to do with the idle on dcoes. 


Okay let me backup. I had the initial timing set at 12*. Total timing 35*. Had the idle AF ratio set at 14.5. Idle was perfectly smooth at 950 rpms which I have read is pretty standard for dual dcoes on L motors. Had the typical dcoe lean flat spot around 2800 rpm during the progression circuit. AF ratios were good all the way up except for right at 2800 rpm under load. It would kiss 18 and then drop back down. No vacuum leaks. I had a couple of options.


The 42's only have two holes in the progression circuit. I could play around and drill more holes like a couple of people have done both successfully and unsuccessfully. Didn't really want to do that because it's a guessing game and I didn't want to ruin the carbs I had.


I could spend the money for smaller carbs, or get smaller chokes which are hard to find and expensive for the 42's. I don't really have the money to spent on new ones. Edit: also could buy a number of emulsion tubes and see if I could tune it out that way.


Since I do not have the capability to hook up the vacuum advance to advance the timing while under partial throttle and under load, I could advance the total timing a touch to give that lean condition a bit more time to burn. Viola! It worked. No more flat spot and actually a bit more power in the higher rpms.


New problem: Now that the total timing is advanced, it is also advanced at idle which caused the high rpm idle. I decided to make use of the dual points to drop the initial timing back down to 12*. That worked great. Now I can adjust the timing at idle independently from the rest of the rpm range. I can adjust the AF ratio back to 14.5 at idle without effecting everything else and I will probably do that. It doesn't make much difference on the idle speed and I only had it set at about 13-13.5 because it seemed to like it after playing with it.


I wanted to play around with it before I spent lots of money on different carbs. And eventually I will probably be swapping the motor entirely. I just thought it was kind of a cool solution and was curious if anyone else had done this before I guess. 

Edited by Luckycharms
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