Read my plugs? This is too lean, right?
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If you're running EGR then what's your vacuum advance?
When running EGR you're supposed to run a vacuum advance block.
Running EGR you normally block the vacuum advance from giving more than around 12 degrees of advance.
Again the reason they do this is NOx.
For the most fuel economy when running EGR run as much advance as the engine will allow.
Ideal EGR for fuel economy, ignoring NOx, is going to be somewhere between the recommended blocked off vacuum advance and full vacuum advance.
When running EGR you're supposed to run a vacuum advance block.
Running EGR you normally block the vacuum advance from giving more than around 12 degrees of advance.
Again the reason they do this is NOx.
For the most fuel economy when running EGR run as much advance as the engine will allow.
Ideal EGR for fuel economy, ignoring NOx, is going to be somewhere between the recommended blocked off vacuum advance and full vacuum advance.
I don't believe there's a vacuum advance block, at least not that I can see. The vacuum line comes off the port on the carb, goes into a tee, with one hose off the tee going to the vacuum advance can and the other going to the TVS on the front of the engine which then exits to the EGR valve.
I changed that vacuum line from ported vacuum to manifold just now and the performance was MUCH improved! I'm now holding 22" of vacuum at idle. I re-tuned the idle screws and it's almost Lexus smooth at idle now. Now, here's my next question:
Should I be running the EGR valve/TVS off ported vacuum, and the distributor off of manifold vacuum? Or does the EGR system not care?
Edit: I believe the vacuum advance maxes out at 12° from the factory, which would put total timing at 36° under full advance currently. There's zero detonation that I can tell, running 87 octane.
Edit 2: I checked the service manual, the mechanical advance adjusts between 11 and 14 degrees with 14-16" of vacuum. So 38 degrees of total timing. I also found the other answer I needed: the EGR should be connected to ported vacuum and the distributor to manifold. That's how the 1979 federal emissions cars are plumbed, which is more or less what this car is now that the FI is gone.
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The block is just a plate that goes in the distributor that limits the advance you may not have it or need it.
With 12 degrees of vacuum advance you probably already have is distributor thats setup for EGR.
The EGR running on manifold vacuum will likely give you EGR at idle and will make you car run like poo, may stall when you step on the gas when in gear.
Ported vacuum gives little to no vacuum at idle, gives vacuum at part throttle and when wide open throttle the vacuum is normally gone anyways so no EGR at WOT.
It's the original distributor, so it's definitely set up for EGR. I appreciate all the help, I need to pick up some vacuum line, once I do I'll run one line from manifold vacuum to the distributor and another from ported to the EGR TVS.
While I agree, there is more to it than just plugging into full manifold vacuum. Smoggers retarded advance at idle via ported vac advance to make the car run hotter, as you said. But they also increased base mechanical, for example from 4* to 12*.
The biggest problem I've had with my iron headded 60's cars is too much vacuum advance causing pinging with crappy CA wannabe "Premium" 91* octane.
Plus, today's gas is different. That distributor might need a full recurve to attain optima results. I would try to manage the lean surge...
But as others have posted, those plugs look pretty good! He ain't far off at all.
Big plus one on that. My buddy never could get his 65 Mustang to run right until I welded up the slot in the advance bar to limit the amount of total mechanical advance and we played with the springs a bit so we could increase the base timing while keeping total advance at a safe level.
Well done. Welded advance slots for the win!
Thank you for all the help, everyone! I cancelled the calibration kit for now; after lubing the advance weights, switching the distributor to manifold vacuum, and retuning the idle circuits and speed I must say the car has never run better.
I need to grab a couple feet of vacuum line so I can clean things up and get the EGR hooked back to ported vacuum per the diagram in the service manual. I'm not sure the EGR system is working, but it is in place, so I'll do some more investigating there.
I need to grab a couple feet of vacuum line so I can clean things up and get the EGR hooked back to ported vacuum per the diagram in the service manual. I'm not sure the EGR system is working, but it is in place, so I'll do some more investigating there.
If the EGR wasn't working, and your distributor is working (with the proper advance) it would be pinging like crazy. You need a great deal more advance with EGR than you do without. That 38 degrees (mechanical and vacuum) that you came up with sounds about right for a 1979 smog engine with GM HEI and EGR
The left two are pig-rich, with the middle being the edge of too-fat. The two plugs on the right are what you're looking for, a light "pencil line" in the radius of the insulator. You have to look down inside the plug to see the fire ring, which shows rich / lean mixture.
Gotcha. No pinging that I can detect, so I must be good!
The plugs look good. There is room to go richer if you want a slightly better throttle response, but make sure you don’t have any vacuum leaks first.
So glad this made such a difference!
The whole deal with ported vs. manifold advance is something I wish I understood the "why" of a bit better.
In the British car community, before the mid-70s, everything used ported advance. MGBs at least went to manifold advance in '72(and dropped the compression ratio a lot that same year)-Triumphs and others made the same change around the same time.
It's pretty widely regarded that this was a negative change, and in fact some change to earlier style carbs specifically so they can run ported advance(the later carbs aren't readily amenable to it, and even people who have drilled for it end up putting the hook up in a strange location due to the way the throttle plate is set up). I actually ran manifold advance at one time, and noticed little difference but what I did notice was mostly negative. Granted the late(77-80) distributors had a ton of both mechanical and vacuum advance, and actually used a rather convoluted system to only give vac advance in top gear.
In any case, I just say all of this because I know I'm talking about a small engine(4 cylinder and under ~500cc/cylinder), where on a lot of American engines we're talking about double the number number of cylinders and in many cases 1.5-2x the displacement/cylinder of a little British engine. There's also the fact that most old British designs are small bore, long stroke compared to a lot of American engines being square or nearly so.
I don't know how that all factors in, but as I said it's just interesting to me that ported advance is seen as an emissions downgrade for American engines, where manifold advance is seen the same way on British engines.
Lean mixtures burn more slowly. Idle mixtures are lean; they need more lead.
As has been mentioned, the early smoggers used less lead to make the mixture burn hotter. Thermostats went from 180* to 195* in many cases.
Low load (throttle blades closed) is high vacuum. Vacuum advance adds lead. Rich mixtures (throttle blades open) need less lead.
So vacuum advance is used to enhance mechanical advance.
That wasn't my question.
My question is more an observation that some engine types(specifically small displacement, small bore, long stroke) were configured for ported advance during the pre-smog era, and moved to manifold advance when smog controls were more restrictive. This is largely viewed as a downgrade, and most will run better on ported vacuum(especially when paired with an appropriate vac can). Of the cars meeting this criteria I'm familiar with, at least one effectively managed a "back door" path to the same result(no vac at idle) by not applying any vac advance unless the transmission was in 4th gear, although that vac came from a manifold source.
Large displacement, square bore engines, particularly those with 6 and 8 cylinders, always favored manifold advance until the smog era, when the switch was largely made(for the worse) to ported advance.
I'm well acquainted with what vac advance does, why it's beneficial for driveability, and fundamentally what's different in the operation of ported vs. manifold advance.
My observation/question/pondering is why do some engine types work better with one type of advance compared to another?
I found some extra vacuum hose on the garage and got everything re-routed and correctly plumbed. I also verified that the EGR system is working correctly, both the valve itself and the TVS that controls it.
I pulled the #2 plug again and looked further down the insulator, as was mentioned earlier. It was a nice, off-white just bordering on grey so I think I'm going to leave the fueling alone for now. I did bump the accelerator pump over to the closest hole, I was still getting just a bit of a lull on low speed tip-in before she caught her breath and took off.
I pulled the #2 plug again and looked further down the insulator, as was mentioned earlier. It was a nice, off-white just bordering on grey so I think I'm going to leave the fueling alone for now. I did bump the accelerator pump over to the closest hole, I was still getting just a bit of a lull on low speed tip-in before she caught her breath and took off.
I really like working on cars from the seventies. I never did get the tuning or timing coordination between EGR and ignition advance.
I did have a 79 Dodge W150 pickup with a two barrel 318 and the 727 automatic transmission. It was the short wheelbase truck. I did find that it ran much better when switching the vacuum advance to manifold vacuum.
I miss that truck.
Did you pull the carb jets and make sure that they are clean, and jetted correctly? They don't look bad. I added a link to compare. Hemmings also has a spark plug chart.
Spark Plug Chart
Every Edelbrock carb I have ran had that stumble @ light cruise. Now you have to change jets or metering rod but you don't know which with out an oxygen senser in the exhaust.
Last one I had got replaced by a Holley after I got few up with it.
Last one I had got replaced by a Holley after I got few up with it.
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