Technical Carburetor Jetting The Old School Way

Yes I know, But I donot mind the tunning , my cousin ran a tun port from a I roc in his 32 5 window 28 mpg , He made all of the harness so it was not cluttered up back in early 90 's driven all most every week from Va to Fla for 10 years ,
Most who want EFI is useing after market system
Like MSD ,Holley ,Fast ,$2,000 -$3,200 NOT $5,000 up .
So if you want all the bell & whistle your going to pay,
The Msd , Holley , Fast you will gain in hp , easy start generic tune & that about it !

 

Aw, jeeze ya should at least take a broom and sweep it off... Show some consideration!!

 

Its a driver
It sets in Rain ,snow the way you see, no hood.
In all these year only a tps go bad , motor is not stock around 350-370 hp

 

Have enjoyed reading this thread; and the techniques some have suggested.

It might be that for "street" tuning, one needs to ask the question "how much is enough?".

But for those that disbelieve the need for checking each individual cylinder where maximum tuning is desired; just check the factory settings on the dual quad carbs used by Chrysler on the street-hemi.

Remember that the carburetor(s) does not directly feed the cylinder(s). The carburetor(s) feed the plenum, and the plenum feeds the cylinders. Pulsing order of the intake valves matters.

But unless one is a die-hard, the above is probably overkill for the street.

Jon.

 

Anyone care to comment on the claim that it's not lean air fuel mixtures at cruise that burns valves or holes pistons? I'll have to dig around where I read that.
edit: HotRod mag. http://www.hotrod.com/articles/ccrp-0507-carb-tuning-tips-tricks/

Says (each engine is different of course), but don't be afraid of AFR of 14.5 or even 15 to 1 at steady highway speeds, as the engine load is very low. Sez it won't hurt the engine.

 

This all started about OLD SCHOOL TUNNING,
the new gas blends off pump will Lie to your Eye !!
Wide band O2 needed,

Yes , lean will burn vales /pistons , Like a cuting torch , depends on load on motor ,
My Self I only run 1 O 2 gauge some times 2 ,
Datta Logger is for everbit of Knowledge on what Each cylender is doing ,
If you have a 8 cly , its not one Motor but 8 individual Cylinders in one package,
One miss tued cylinder will darg the others down ,
I have even Ran different spark pluges in each cylender , diffrent jets from side to side ,,
Ther is somuch you can Do , Hell !!! I know of guys that have diffrent Lift grinds for each cylinders diffrent and So on , ( thinking out side of box) Just think as if its 1 cylinder and make all run efficient ,
THEN YOU HAVE ONE BAD A$$ MOTOR

 

My Falcon has Rochester/GM TBI EFI on it, and it controls the timing.

 

Anytime When the manifold vacuum is high and your timing is perfect you can be right on the perfect stoichisometric of 15:1. The efficiency is highest there but That is an unforgiving place, only for the perfect people and engines that have each cylinder perfectly equal and never bobble. Knock sensors are pretty much a necessity in my opinion if you need that type of efficiency. 15.01:1 is the technically lean and 14.9:1 is technically rich. 14.7 is a bit more lovable and livable at high vacuum conditions.

One cylinder with a random miss fire or the bank random misfire will send the guage read lean.

 

One thing I've been meaning to do, somebody mentioned it here, is have a look at the ignition waveform on a scope. I can recall when shops had those big Sun machines and oscilloscopes and using a trace could diagnose all kinds of stuff quickly. I don't know anybody with a scope though. Do the shops use something similar today? Probably everything is OBD2 today hm. It would be nice to verify that yep, ignition is good and hot and fat and no misfires or attenuated or whatever.

 

I still have one in my shop.

 

If it was a little warmer I'd prolly take ya up on that...

 

Well the LM-2 AFR meter arrived on my doorstep today. Any tips on how to do this? One thing I'm reading is to start with the idle AFR naturally, and run it up to around 2000 to 2500 to get a ballpark on jetting. One commenter mentioned not to get too hung up on the numbers, each engine is a little different, and to make allowances considering that the leanest cylinder may become too lean if the operator tries to follow the "perfect" theoretical numbers. A cold engine will read rich at first, and then lean out when it is fully warmed up?

 

It takes a while to understand what the LM2 is telling you. Do you have the insert gizmos for both exhaust pipes? Need to get them up in there as far as possible or they'll read lean due to reversion. You have to let the sensors warm up before taking any readings. I tape the harness' to the cars' body and then get somebody to drive, you'll be able to read both pipes with the LM2. Drive and tweak, the hardest to dial in is town driving esp you have big motor and cam, if you're on the stock side you'll get good pretty quick. I find about 12.7 to 12.9 will give you good drivability.
Its an interesting tool, you can download to a chip and play it back on your computer.

 

He is running O2 sensors just downstream of the manifolds.

 

Held off on the bung installation, the LM-2 has a 1" tall bung, they recommend that the sensor tip itself end up flush with the exhaust pipe. The bung I had bought previously is considerably shorter, so decided to wait. Maybe will find an exhaust shop open tomorrow to weld it in. Not sure it makes that much difference but, they wrote the manual. It calibrated fine in the open air so it's ready to go.

 

Maybe you could use a spark plug anti fouler to move it out of the short bung.

 

Here's your anti fouler.
Same thread as the O2 sensor. You need to drill it out but it's easy.
Pretty common trick - when changing to high flow cat converters or universal you need to move the rear 02 out of the stream

 

A flamethrower might be a necessary addition Are they used in the same location as the O2 bung??

 

They screw right into the welded in or existing O2 bung and then the sensor screws into it.
It pulls the sensor out of the exhaust stream, a spacer if you will or a substitute for a 1" tall knot of bung hanging off your pipe

 

Sorry, I misunderstood. I thought you had the Innovate LM-2. It sounds like you have something else.

 

Innovate LM-2, that's correct.

 

Well I got around to installing the O2 sensor bung in the exhaust. Just one side for now. Haven't had a chance to drive it and test cruise or WOT ratio but it was warmed up well from the drive home so I checked the idle A/F ratio in the garage, it's cold out here around freezing. It was lean, right at 16:1 with oil bath on, adjusting the mixture screws it seems the display is pretty responsive. Just a small turn of the mixture screws makes a big change in the A/F. We checked carefully for exhaust leaks prior, as these will bugger the results. It seems like the standard tuning by ear - back off mixture screws 1/4 turn from when idle starts to drop off - is dead on at 14.7. Should I shoot for highest vacuum and smooth idle and ignore the A/F number or, shoot for a little richer than 14.7 at idle?

I'm beginning to see why efficiency and carbs was a problem, they had to work well from ten below zero to a hundred and ten with (usually) no adjustments at all by the end user. With todays gasoline basically boiling in the carb in hot weather I am guessing the mixture goes VERY rich.

Can't help but think jetting changes, at least maybe a size or two would be required between winter and summer for optimal tuning?

 

If you are using E10 gasoline, Stoiciometric would be 14.2:1, if I remember correctly.

Winter versus summer should be made by direct observation of your setup. No formula will be truly accurate.

 

No corn squeezins, since it doesn't store as well. On a road trip it wouldn't be practical to try and avoid it though.

So let's say we get things dialed in with the idle A/F ratio mixture screws at stoich and the steady hwy cruise A/F at stoich or even a bit lean with the jetting.

That leaves the accelerator pump circuit and (mostly) power valve for WOT enrichment and heavily loaded conditions.

Except, with a MC 2100, there is no metering block. Nothing to adjust, or drill afaik. If there were, not sure I'd want to. Lots of carb guru wizardry going on with those metering blocks, by drilling out PVCRs and the rest of it.

Am I likely to find the Autolite engineers were good enough where it will likely be more than fat enough on WOT or heavy load conditions, assuming everything else is tuned proper, or maybe even pig rich? Could maybe snake some thin wire through the power valve channels if it was too far on the rich side. But if it's way out lean, what are the options?

Still want to check the plugs careful even with the wideband, right? Consequently is there a better plug to use for this, e.g. on a Y block the #5 plug is the easiest to get to but, maybe a certain cylinder or two tends to run lean compared with the others. That would be the one to keep an eye on I'm thinkin'.

Due to shared exhaust outlet the middle cylinders can run hotter, maybe that's not the same thing though. Thanks for the advice gents, it's real helpful.

 

Oh, and one thing that a EFI does that a carburetor simply cannot do is altitude compensation.

My regular operating range includes 10,225 feet of elevation change. That would probably mean stopping to re-tune thee times, for each grade, up, and down.

I'm not going to do that. Yeah, it ain't traditional, I don't care. I built my car to drive, not sit on the side of the road, getting re-tuned, while my wife gets pissed-off.

 

Uhh, I gotta change the jets

 

Especially if I have had coffee.

 

I'd think you'll find it'll run strongest at 12.7ish depending on cam etc. With stock mild economy cam you can lean it out quite a bit closer to the 14ish range but most performance motors will want to let a bit of fuel on by and if you lean them out it'll run hot,weak and rattle.

 

I pulled these plugs out of a 46 truck I bought about 6 yeas ago. As you can see the previous owner was a wiz at dialing in a carb. Hell he was so good he was able to use plugs of all different lengths, and one without an electrode on the end.
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