Hi guys, I have a rebuilt LG4 CCC Qjet on top of my 1987 305 TPI long block. The 305 TPI long block is totally, totally stock. It runs well but I can not get the idle rich enough. No matter what the IAB dwell ranges around 15-20 degrees in closed loop. I can almost get it up to 30 degrees with the IAB turned so far that it is almost all the way out the top of the air horn. I have tried turning the idle mix screws out a half turn at a time. I started at 3 turns out and am now at 5 turns out. Still no dice. The richer I make the idle the better the car runs but I can't believe that a stock 305 needs to be this rich. It is a roller cammed motor but it has a 0.350" peanut TPI cam so it's not like it's high performance or anything. Help!

 

Since the carb was rebuilt, the MC rich and lean stops may have been moved. There is also the possibility of a low float level, or a TPS voltage that is too low. There's a good chance that they at least need to be checked/reset. Rather than reinvent the wheel, this link may help:

ADJUSTMENTS

About halfway down the page are instructions for presetting the MC solenoid travel.

 

MC stops were not moved. MC solenoid travel is 4/32", within spec. I hate this carb!

 

When I rebuilt mine last summer, the kit said to put the mixture screws at 4-1/2 turns out. I forget the details on where it said to adjust the IAB, but I used the normal adjustment tools for the rich & lean stops. When I adjusted the carb on the car, I had to move the IAB about 1/8 turn to get to 30 degrees.

If your O2 sensor is doing its thing, then I don't see a problem turning the mixture screws to get the dwell right. Put the IAB about mid-range, then use the mixture screws to get to 30 degrees.

 

Five7's right. I'd go 7 to 8 turns out before feeling a little uncomfortable and readjusting rich/lean stops. Keep in mind though that out with the idle mixture screws will richen the mixture (dwell increase) and out with the IAB should lean the mixture by letting more air in.

Thought you were dialed in with this?

Read your other post and I'm going to double check the action of the IAB.

 

Yes, please do that. I'm going by memory that the IAB screw has a RH thread so that turning it CCW will raise the stem out of the orifice.

 

Double checked the IAB screw and turning it out (CCW) leans the mixture resulting in lower dwell readings. Did this on the car as my carb book has been loaned to a buddy. Was pretty certain but like Vader, it's been a while.

Could there possibly be a mechanical problem with the plunger/spring/clogged bore/passage that is allowing it to behave oddly? I've pulled these apart and found bent/sticking plungers that may cause symptoms like these, but that's supposition on my part.

I'd set the IAB at 4 turns out then follow Five7's advice with the mixture screws before doing anything else. You do have a ranging dwell, right? Choke the carb and dwell changes?

 

Vacuum leak or a bad O2 sensor?

When properly adjusted a cc-QJet system can feed a wide range of engines reasonably well. A mild 305 TPI long block shouldn't act hardly any different than the original LG-4 as far as the carb is concerned.

4-5 turns out on the mixture screws for a stock QJet is not anything to worry about. I often start at 5 and find it's damned close on most motors. That's with the IAB turned up about 4 turns from lightly seated. Make sure the o-rings on the IAB body are in good shape. There are 2 of them. Big one on the top groove, little one on the bottom groove. If they're chewed up or missing it'll never work right.

BTW- the IAB affects idle mixture in the OPPOSITE way from the idle mixture screws. Out (CCW) is LEANER. In (CW) is richer. The thread on it is still just a regular right hand thread but remember it's an adjustable AIR BLEED, not an adjustable fuel restriction like an idle mixture screw is. So it works opposite. More air through the IAB = leaner, less = richer.

 

The O2 sensor is a genuine Delco 4 wire heated. I had this sensor on my TPI based 327 for a few thousand miles and it was fine. It behaves the same as any narrow band Delco sensor but it has isolated grounds for better noise isolation and a heated element for faster warmup. It does range properly, I think the carb is just out of whack at the moment from too many adjustments. I also have the intial timing up too high because I suspect the balancer spun and was timing by ear. I know the timing will affect the O2 reading if the carb calibration is not changed. I got an adjustable TDC piston stop to reset TDC on the balancer. I'll get the timing dialed in and go from there, starting with 4 turns out on both the screws and the IAB. I'll let you know how it goes. Thanks guys!

 

I'm running a heated O2 on the camaro (O2 in y-pipe, coated hedders didn't have bung) and it functions perfectly. I think once you've got the timing set and carb at 4 turns out everywhere you'll be gravy. That's weird with the IAB acting odd though. Let us know how it turns out.

Mike

 

I just realized I never responded to this post. The end result is, I never got the CCC system to adjust properly. I have tried 3 or 4 factory sealed carbs and another brand new genuine delco 1 wire sensor and I still can't get the car to run right when the dwell is around 30 degrees. I wish there were an Edelbrock or Holley carb that was made w/ a TPS in it. I know I can retrofit a TPS to an aftermarket carb but that will probably result in something awful running as well. I really didn't want to have to go TPI on this car because the 305 is so weak, it should be good enough with a properly adjusted carb, but apparently not .

 

You mentioned timing. Did you get the timing set before more ccc adjustments?

 

Of course I did. I even had the heads off and verified TDC with a dial indicator to make sure the timing tab and balancer were dead on TDC index.

No matter what carb I use, and even with the brand new delco O2 sensor, I get the same result:

Turning the idle screws IN (lean) or the IAB OUT (lean) makes the dwell reading INCREASE. This is the opposite of what should happen but without a doubt, and repeatably, this is what happens. I have to bring the idle screws in to only 2 turns out from seated, and I had to bring the IAB out almost 5 turns, to get the dwell to even range around 25 degrees. If I bring the idle screws out to a more normal setting, 3-4 turns out, and the IAB to around 4 turns, the dwell bottoms out at 10 degrees (full lean). This does not make any sense but it's what my system does. If I bring the revs up to over 1500 the dwell is ranging right around 30, and when I rev I can see the periodic rich and lean spikes in the dwell, so the system is going closed loop and ranging. I can hear the EGR solenoid buzzing once the car is up to temp, so that also verifies it is definitely going closed loop.

I get no check engine light w/ the dwell set to around 30 degrees at idle, idle screws 2 turns out from seated, and IAB nearly 5 turns out. With the IAB "set" according to my screwed up reverse-acting dwell response, the car runs decent and is responsive enough but it is a little flat and lean off idle. Most people would just leave it alone at this point and call it done but I am not happy with why the computer thinks the car is over rich until I lean it out so much it barely runs right, and then the dwell starts going the wrong direction.

What does not make sense, is why my dwell readings are behaving in reverse of what they should. I have been troubleshooting this piece of crap CCC system for over a year and it has always done this. This car is begging for a MAF TPI conversion like my previous carb to MAF efi setup.

 

Double checking something before posting....

 

I can't find my damn dwell meter- I think it's on my boat (becuase it's old and has a points ignition) and it's put away for the winter.

I'm going to take a stab at this anyway, just going by what I can remember off the top of my head....

Point 1: You've tried enough carbs that I think we can agree that the problem is not with the carb. You're seeing consistent results from multiple different QJets. I know from your previous posts you actually turn wrenches before you post stuff up so I'm going to pay you the complement of saying that I trust your observations completely as being accurate- not that you simply misread something simple or posted something you made up out of thin air.

Point 2: I think you're interpreting your dwell meter readings backwards, not that your car is working backwards.....

When I use my dwell meter for it's original intended purpose (setting point gap in a distributor), as I recall, the reading goes higher the larger the point gap is. When the points are open the coil is firing (no voltage passing through it). When the points are closed the coil is charging (voltage is passing through it). So the greater the point gap, the higher the dwell reading, the greater the open time (no voltage). The smaller the point gap, the lower the dwell reading, the greater the closed time (voltage applied).

Applying those observations to your cc-QJet, that would mean the lower the dwell time, the greater the circuit to the MC solenoid is powered (energized). So a low dwell reading would indicate that your MC solenoid is being energized for the longest time the ECM is capable of energizing it withing the limits of it's code (10*, apparently). And an energized solenoid means the power piston is in the DOWN position (lean).

In short, your ECM is trying it's damndest to lean that mixture as far as it possibly can (higest energized time possible). It goes all the way to the bottom of it's range and sits there, just wishing it could go further (leaner), but can't.

Then you come along and lean it out mechanically with the idle mixture screws and IAB and it finally gets lean enough that the ECM can come up out off the bottom of it's adjustment range- it finally has a little "room to play", and your dwell kicks up to a higher number.

So, if you're with me so far, where we're at is that we AT LEAST have explained that your cc-QJet system is working the way it's intended to, not in reverse! I.e.- it's working "sanely" and the resuts you are seeing are absolutely true, correct, and reliable. You can take a breather now becuase that means YOU are not insane, and neither is your car!

Now the big question/problem...... so why do you need to lean it out so far to get a "sane" dwell reading. Well...... that one I can't help you with. I honestly don't know. A stock 305 TPI motor shouldn't be all that different at idle than the original LG4 engine was. Probably it's some quirk becuase of the combination of cam/heads/ignition timing. Maybe it just runs real efficent at idle and doesn't need as much fuel. Maybe at idle your throttle plates are open far enough you're already up on the intermediate circuits too much, fatting the mix and requiring you to lean it back out again by other means to bring it into spec. Maybe your fuel pressure is too high and causing a high fluel level in the fuel bowl at idle. But I can tell you with some certainty (if what I posted above is correct) that it's not the carb, a flaky O2 or a bad ECM.

You might want to print this out and sleep with it under your pillow tonight.... I just re-read it and I sound like a mad scientist with all the "if this/then that" logic. But I'm pretty sure it's all correct, if not easily understood. You done good- I think you're just interpreting your observations backwards.

 

I appreciate your input but I disagree. The Qjet manual explicitly states that, when adjusting the IAB, to turn the idle screws counterclockwise (OUT, richer) if the DWELL reading on the meter is below 25 degrees, and to turn the idle screws clockwise (IN, leaner) if the dwell reading on the meter is above 35 degrees.
I get the exact opposite reaction on my dwell meter.

I wish the answer was as simple as me misinterpreting the meter, but it isn't. I have spent enough time with this system to rule out user error.

So the only thing I may be able to rule out is the carb, that's it. The system is still totally hosed. I hope I find a complete TPI parts car in a u pull it junk yard so I can get the whole harness and ECU without having to piece the wiring together.

 

Got to agree with 327. Dwell reading for the MCS is a direct measure of its cycling (up and down). Default position of the plungers is up, out of the jets. The more it cycles (higher dwell reading) the more time the plungers spend down, in the jets-restricting fuel. In fact we're not using the meter to measure dwell for the MCS but 'cycle' time.

I do however agree with Damon that it's probably not the carb(s). I thought his idea on the evap canister had some merit. Seems as though the system is too rich at idle and this rich condition goes away (or becomes less noticeable) with more throttle and/or adjustment changes.

This problems got me perplexed and I really hope you figure it out.

 

Yep.

The problem still is, regardless of whether I had a problem like vapor canister enriching the idle, why the system is leaning out the mixture as I am further leaning it out, instead of enriching the mixture as I lean it out. It is responding totally backwards and screwed up. I don't think it is ever going to run right if it can't react to input properly. If anyone has an 83-84 LG4 ECU, please let me know, I will try swapping it out. I had a spare but I threw it out.

 

Does dwell decrease (enrich) when the air horn is choked, as well?

 

What does your dwell meter read if you don't connect it to anything? Just leave the wires hanging out in the breeze.

Also, when it's sitting down at 10* (closed loop) what do your O2 readings look like? If it's actually rich they should be high.

I find it practically impossible to believe that the system is operating backwards.

I take that back..... ONE thing I can think of that has driven me bonkers before was a miss at idle. If it's got a misfiring cylinder the O2 will read as "lean" (lots of unused oxygen in the exhaust) and the ECM will crank it rich to try to compensate.

 

For the sake of technical correctness, that isn't quite right. Dwell with a points distributor was the time the points "dwelled" closed. The wider the point gap, the less time they will be closed. For the MCS, dwell is the amount of time the solenoid is energized. A 6 cylinder engine has 6 lobes for the points, or 60 degrees per lobe. 30 degrees dwell, therefore, is a 50% duty cycle - the MCS energized half the time.

I suspect, too, that the problem isn't in the carb. And probably not the ECM. Something that "fools" the O2 sensor makes more sense, such as a slight miss, or a vacuum leak on the non-O2 bank.

 

Meter reads 60+ degrees (max on 6 cyl scale) disconnected. So the "higher" up the scale the needle goes (left to right sweep), the lower the dwell reading gets.

Out of curiousity, was your miss at idle a mechanically induced miss or an electrically induced miss? I will check cranking comp on the O2 bank to verify the valves and rings are all up to snuff.

 

My meter reads the opposite. Left to right is higher dwell with 60+ pegged to the right and mine sits at the left end disconnected (<10). Weird.

 

Ah hah! I'm not so crazy after all, am I?!?!?! So we've got 2 different dwell meters reading OPPOSITE eachother under identical conditions, eh?

Methinks we're getting to the bottom of this.

I WILL DIG OUT MY DWELL METER TODAY- and we'll see what it reads, too, for comparison purposes.

The miss I had was vacuum-leak induced, near one cylinder causing a nasty skip at idle, but going away at higher RPMs.

 

Extensive testing and checking complete. Short answer: I wasn't crazy and neither are you.

First off, behavior of my Dwell Meter: With terminals hanging in free air it reads 0*. With terminals touching eachother it reads 60*. Don't know if that's right or wrong, but that's what mine does.

I then had to mock up an entire cc-QJet setup becuase I don't have a car that uses the system handy. Got out a battery, some cables and clips and hooked up an old telegraph key to simulate the on/off of voltage that the ECM does to the solenoid. You can do this with 12V becuase that's what the ECM uses (not 5V like all the sensors are). Made sure it worked as it should- MC solenoid in the old carb was clicking every time I applied voltage and I could see the plunger go up and down as it should, since I took the IAB out to have visual verification.

Hooked up the dwell meter to the MC solenoid termianls and.....

With voltage removed (MC solenoid de-energized/up position/rich) it tops out at 60* on the dwell meter. Makes sense since this is almost exactly the same as touching the terminals together in free air (see above) except with the very low resistance of the MC solenoid in between.

With voltage applied (MC solenoid energized/down position/lean) it bottoms out close to 0* on the dwell meter (flattens out around 4*).

I tried it by reversing polarity first at the solenoid and then at the meter- made no difference. Read the same way regardless of polarity.

So it's happening exactly like I described, above. May not be what your meter does (sounds like it is, though), but that's what mine does. Long story short, I think the mystery of the dwell meter is solved (some of them read backwards or the manual you are reading is wrong). You're still not nuts, your car still isn't nuts, but your dwell meter might be, jsut like mine!

 

We're using a dwell meter, designed to measure the degrees that the points in a breaker type ignition system are closed, to measure duty cycle time. My recollection is that maximum cycling of the MCS is 60 times/second which would correspond to 60 degrees on the meter. Units aren't important, though, as long as we agree that higher meter reading (displayed as degrees) corresponds directly with more cycles per unit time. Essentially like a tachometer, which a dwell meter can also measure.

I've got a cheap, little Actron meter that is not self-powered. Two terminals: a sensor lead and a ground. Touch them together and nothing changes. My meter has a selector switch for dwell/tach/voltage.

The meter receives a signal on the diagnostic lead every time the MCS cycles (is pulled down), compares it to ground and displays a reading depending on how many of these signals it senses over time.

Not sure the above added anything or that your test was definitive. Just further discussion, I guess.

 

I'll add that my meter IS powered (it's digital).

A dwell meter doesn't read the number of cycles, it reads the on time vs. off time. The MC solenoid is cycled about 10 times a second by the ECM. That's consistent and never changes. It's how that tenth of a second is divided between on time and off time that determines the dwell reading.

That's why when you read dwell when setting a points ignition the RPM you check at doesn't matter. It cycles faster the higher you rev it but the dwell doesn't change becuase the percentage of on time vs. the percentage of off time doesn't change. Don't try this on an electronic ignition like an HEI, for instance- they have "smarts" built into the module that varies dwell based on RPM (at least up to about 3000, then it flattens out and remains consistent).

A tach DOES care about how many times it is cycled- in fact, it doesn't care at all about the on vs. off time. It just triggers off each positive hit coming off of zero. More hits, higher reading.

 

That's contrary to what I've read but much of what I've read is contradictory anyway. It also makes some sense. The meter would then be reading actual dwell of the MCS with degrees converted to % of time 'on' or in the jets. Higher % more time 'on'. Same result in the end but there's a distinction that I want to make sure I'm on the right side of.

I'm still having some trouble with your test however. Seems you've taken a device designed to compare a rate over time ( or say a rate open vs. a rate closed-one rate over the other would be dimensionless) and are applying a steady state condition to it. Not sure it's definitive.

Oh and I remember using a dwell meter a long time ago on a points type distributor. Don't remember much though.

 

Forget the dwell meter. Scan with a tool like Auto Xray, it'll give duty cycle in %.

 

Then there's that, but I still want to be certain WHAT we're measuring.

I think also that Damon suspects some meters may be providing a reading of duty off % which may explain why 327's system appears to be responding opposite convention?

 

this might make a good sticky -

I have an old Actron... guess its a couple years newer than the carb though!

 

Naf- true enough, I was doing a steady-state test so I just did it another way, by trying to do my best to hit a steady cycle time on the key with my finger. It took a little practice but I can cycle accurately enough to hit just about any dwell time in between that I want. I got good at holding ~30* (50% on/off) and then went to just tapping it quickly and could get it up around 50* (mostly off time/needles up/rich) and then holding it down and only letting off for short periods of time (mostly on/needles down/lean) and got it down around 15-20*. Now, I'm not as accurate or as fast as the ECM but I'd estimate I'm running about 3-4 cycles a second. Everything seems to work and give readings that are consistent with the steady-state tests. My dwell meter reacts rather slowly so a low number of cycles per second doesn't produce widely varying numbers. They stay confined in a pretty tight range.

This would make sense since dwell is often measured in an old distributor while just cranking on the starter and that's only about, what?, maybe 50-100 engine RPM, or about 4-8 firings/cycles per second. Something slow enough that a "twitchy" meter would be worthless.

 

Where are we now? Ignition dwell is defined as degrees of camshaft (?) rotation in which the points are closed. Higher readings would indicate the points are closed more (vs. open), up to 60 degrees maximum for a 6 cylinder (so it must be cam degrees, right?)

Oh and two other definitions I've confirmed (thanks):

Duty Time: # of plunger cycles per second
On Time: Duration of time plunger is down during each cycle-we're measuring this with the dwell meter converting readings in degrees to %.

I'm still convinced that higher dwell readings indicate longer On Time=CCC leaning mixture (responding to a rich condition). Remember the dwell meter is connected to the points terminal on the ignition coil (and a ground). Am I right? There's been a lot of thinking going on.

From a random web page on setting point gap: "If it (dwell reading) isn't in the middle of the allowable range (say, 24 degrees when the range is 20-26 degrees) stop the engine and move the point gap closer to raise the dwell or farther apart to lower it."

 

Dwell readings on a cc-QJet have nothing to do with crankshaft degrees since the ECM cycles the MC solenoid 10 times a second regardless of engine RPM. On a points distributor it DOES indicates cranshaft degrees of open vs. closed times since the distributor rotates in time with the engine.

Dwell meter in a points-type ignition is hooked between the neg. terminal on the coil and a ground.

Can't say why what I'm seeing is different from what the book says about point gap and dwell time. Maybe my meter is backwards (and I think maybe 327's is too?). That could be the key to this whole thing- some meters reading backwards due to their (incorrect) design.

You ain't just whistling dixie on that one, brother! I've had to think my way through a lot of this stuff over and over again. I'm also wondering if I've been setting the points wrong on every motor I've ever used this dwell meter on, which fortunately, has not been many.

 

Dwell is in fact the amount of time the points are closed - or, to put it another way, when the circuit is powered. If opening the points gap decreases dwell for you, it's backwards. Reading off of the ALDL will resolve that.

 

Like I said, I have explicit instructions from the factory manual on setting IAB and idle screws, that assume you are using a dwell meter, and tell you which way to expect your dwell meter to move based on idle/IAB changes. So the only possibility is that my meter is backwards from the meter they had in mind when they wrote the factory service manual. However I can't imagine that any two dwell meters could be flip flopped from each other. A dwell meter that doesn't read dwell wouldn't tell you anything useful. So I am following the FSM to a T, using the tool they specify. It is an older Sears unit w/ 4, 6, 8 cyl scales, all on the same gage face.

Even if my meter were flip flopped, 50% would still be 50% duty cycle, no matter whether it was on or off time. So that doesn't explain why I need to lean my engine out so far it barely idles to get 50% reading. The car runs much better using "baseline" settings but then the meter is pegged off the scale.

 

327: Yeah, we've gotten a little far away from a discussion of your specific problems (some outlined in another thread) but it's been fun and interesting and I appreciate your patience.

And yes, we could just use a different tool (autoxray, etc.) and avoid the problem of defining MCS dwell and how the meter works. It seems though, at least for me, that too often in the real world we're forced by limited time and resources to accept the quick, pragmatic solution then drive on to the next problem. Too often we're not allowed to delve into an issue and try to determine what's REALLY right and WHY.

Eh, I've got an engine to take apart this weekend and a change order to get approved before I leave work...

 

You gotta remember that even at the proper 14.7:1 at idle that is DAMNED LEAN. If you were tuning the idle without an O2 just going by vacuum readings and such you would say "wow, this thing is running real lean!" Most non-computer controlled carbureted engines tuned the usual way will actually be around 13.5:1 when the guy doing the tuning feels that it's running right and properly tuned. That's almost always true.

Don't know why your engine wants the idle mixture turned down so lean to run right but I have about 100% confidence at this point that your O2 and ECM are working properly. Your dwell meter appears to be working the reverse of what the book says it should (as does mine) but the systems are working and adjusting the MC solenoid the way they should should.

I don't like this answer either, but there's no other conculsion supported by the facts. Maybe chuck in a new ECM & O2 if you think yours is flaky but the dwell reaction to your idle mixture adjustments will still be in the same direction as you are currently observing.

 

327- I just had one more thought...... but I need to know EXACTLY how you are hooking up your dwell meter on the car when you're doing you testing.

 

It only functions one way, can't hook it up backwards. I am probing the 2 leads on the MCS (one is just a ground lead anyway, you could ground to the body and get the same effect). If I swap the polarity I get nothing at all, the meter does not work, so it has to go one way. This puts the "red" lead on the hot pink/black tracer wire, which is key on hot anyway.

The factory ecu only targets 14.7:1 at idle and cruise. The fact is that the car should run fine without popping, w/ a stock engine and calibrating per the dwell specs. I'm not saying it runs fine stock and runs better over-rich. It runs like crap if I believe the dwell readings, and fine over-rich. I have a big nasty roller cam in a 327 that has MAF EFI and I run it closed loop, 14.7:1 idle/cruise, and the car runs flawless. This junk 305 should too.

Plus when you calibrate 14.7:1 idle, and cruise, the carb is still mechanically allowed to go way richer than that under enrichment (accel pump) and WOT (secondaries). This is not the problem.

If anyone needs CCC carbs, I have a whole handful I will be unloading. They are all 83-85 305 or 350 passenger car carbs. I also have an aluminum qjet manifold.

 

Do me a quick favor and do it this way: find the single wire blue/green dwell connector sticking out of the wiring harness near, I think, the rear of the motor. Attached one lead there and the other to a ground (carb body or whaterver's handfy). I have a hunch. AND it's actually the factory-specified way of checking MC dwell. I don't know the polarity doing it that way, but like you said, your meter only works one way (mine works both ways becuase it's digital and has some smarts built in for reverse polarity).

I'm seeing "backwards" dwell on my bench test doing it the way you're doing it now. Let's try the real factory-specified way.

If suddenly you see the dwell numbers work the way the manual says, then I think I have an explanation. Not to mention we'll have critical info for any board member who ever checks their dwell in the future.

 

Uh oh you are asking me to dig through my rats nest wiring harness. What does this connector look like, is it a plug in connector that has nothing in it right now? Do you have a pic? Is it blue or green, or is blue/green denoting blue with a green tracer? Is it fed from the ECU or is it inline w/ the MCS solenoid?

If people telling me to back probe the MCS has caused this problem, then ... well that will be pretty funny. That will also tell me that there are a whole lot of LG4s that are not calibrated correctly.

 

Pic is from an 87 LG4 but my 85 has the diagnostic lead in the same place. Adjacent to the working A/C.

 

I found the dwell diagnostic connector and I do get a reading when I use it. I didn't have time to warm the car up enough to get it to range but it does work. I will report back when I get it into closed loop and check the readings back to back w/ back probing the MCS.

 

The award goes to Damon for figuring this one out. When I connect dwell to the diagnostic MCS connector and ground, dwell goes up and down correctly according to rich/lean. I am able to achieve 30 deg dwell now. The IAB screw is around 5.75 turns out w/ the idle screws 3.5 turns out each.

So... all of the posts on this board that tell you to backprobe your MCS (even the sticky I think tells you to do that) are incorrect, at least when using a conventional old dwell meter.

 

That's the one- single blue/green male blade connector.

It's just a THEORY at this point. Your testing will tell us if it's correct or just another one of my hair-brained ideas.

PS- I've always done it like you have been doing it, but if I'm shooting for 50% duty cycle/ 30* dwell it's 50% either way (correctly or reversed) and I don't pay much attention to which way I'm turning the screws if I'm only off by 5-10*. But if you're hitting the limit of the range...... well, you get the idea.

 

You're right, I tested and calibrated the car tonight, using the MCS lead. I get a flip flop reading if I probe the MCS, vs. using the MCS lead. I was so far out of the range that having the dwell going the wrong way, made it hard to figure out how to get back in the right range. Now when I want the dwell reading to go down numerically, I turn the IAB out, and when I want the dwell to go up numerically, I turn the IAB in. This is exactly the opposite of how the dwell was behaving probing the MCS.

The idle screws and IAB had very little effect until I finally got close, then 1/16 turn of the IAB would way overshoot 30 degrees, and I had to make very small adjustments to get it right over 30.

 

Ah, good. Sanity returns.

Get used to the new readings and try different things out for a while until you get comfortable with it. It shouldn't be any more or less touchy than doing it the other way (it's still measuring the same thing but in reverse). And let us know where your settings end up at on the mixture screws and IAB. They should still want to be set lean like before, but the readings should now agree with what the manual says should happen as you adjust richer or leaner.

I'll post up an explanation tomorrow.

 

With the 3.5 turns out on the idle screws. 5.75 turns out IAB, I have 30 degrees ranging dwell. I could probably achieve the same thing w/ the idle screws in a little and the IAB not out so far, but since I am out less than 7 turns on the IAB to achieve 30 deg dwell, it should be fine the way it is.

 

You've found the sweet spot and you're not too far out of range on idle mixture or IAB. Now you'll have to go back and edit all those ccc-qjet bashing posts...