comments inside the quote
So went with carb #3(another 1405) and set the Tport sync. Also removed stock orange 5" step up springs with yellow 4" ones.
So adjustments/readings.
Idle at 700 in park Good
0 vac at dist port on carb(pass side) very good
19* initial
Fulltime vac 15" pretty good
I then adjusted timing slightly moving it up to 20*
Adjusted idle mix screws to maximize vacuum. was able to get 15.2"
Idle now was 775 in park Getting to be a little fast for a 270/270/110 cam
So made some more tweaks to help lower idle rpm slightly, Im aiming for 700-750
Idle 750
Max vacuum I could get was 14.5" at idle(750)
Intial timing 17*
Timing at 2000 rpm was 23*
Vacuum at 2000 rpm was 18.5"
All better
Took it for a quick rip and seems good, but always looking for better. I think it liked the timing advanced a degree or 2 more.
Throughout all the tweaks adjustments I havent had any pinging. So it likes the timing, but it raises the idle up a bit more than I would like.
I didnt get an "all-in" as Im doing this outside and it was getting late.
I will tweak with it a little more today.
Thanks all!
Pics of 1st Eddy 1405, where I couldnt get Tport sync adjusted correctly. More noticeable in person.
Ok so you are figuring out how to sync the T-port to the timing and the resultant idle speed.
The T-port sync being square is not a hard and fast rule. It can be slightly taller than wide. But when you do that the lowspeed circuit goes rich. So then you tighten up the mixture screws in an effort to make the idle smoother. So now it idles nice, but the part throttle goes rich. And of course the idle speed goes up. So then you take some timing out to get the idlespeed down. This is exacty what you are doing; namely chasing the idle speed around with the three parameters that you have.
There is are two other tools you can use to get a too-high idle speed down, actually three.
But first reset the T-port sync to square to slightly taller than wide, and LEAVE IT THERE!. then set the mixture screws to 1.75 Turns from lightly seated, and leave them there. Next reset the timing to get the rpm down to 600/650 in first gear. Yes brakes locked or whatever it takes to not have an accident.Try to set the idlespeed down closer to 600 if the engine is ok with that, BY USING TIMING. But if the tranny doesn't BANG into low then you are free to get closer to 100/150 to your target Neutral idle speed.
What I mean is if you are targeting 700N, then 600 in Low may not be low enough. Why is this. Because the little 273 does not have enough torque at low rpm to fight the TCs stall.
Say you have a stock 2bbl TC that was rated at 1750. Now with the 270 cam, the stall might be down 100 to 150 lower due to the traded away torque. So now with a 1600TC the thing is wanting to pull very early, and the IDLE-DROP is reflecting that. So what is the solution? Typically the solution is more idle-timing. This starts the fire burning a little earlier, which may create a better-timed push on the piston, and creates more torque, and so the rpm drop into low is less drastic. But the increased idle timing has baggage, namely a higher Neutral rpm.
So what's the proper solution. Well the stock TC would have to go. We would need a looser one, so that the idle-rpm does not get dragged down into the basement when a comfortable no-load pm is targeted. This also usually softens the hit into low from N/P.
Ok but say you had a hypothetical 2400 or looser TC. This should present a smaller rpm drop into gear. And thus the N-rpm can be set lower.And the idle-timing can be adjusted to reflect that you no longer need the torque.
But say you already have a 2400 or better TC installed in your car. And you are still experiencing a large rpm-drop no matter the idle-timing. We still have two tools.The first is wet fuel level in the bowls, and the second is idle-air bypass.
As to the wet fuel level.
When you set the dry fuel level according to the instructions, those instructions are targeting a wet fuel level, designated by the designer. He designed the carb to run on a particular wet-level, with a particular fuel-pressure,in a particular environment, and working backwards arrived at a THEORETICAL specification for dry-setting to achieve the wet-level. So if the carb is not operating at the design parameters, then it will not be operating at the proper wet-level. So if you think about that for just a sec you will get an AH-HA! moment and realize that the spec dry-level is not written in stone.
Ok but how can this information be helpful? Well, the low-speed circuit is very sensitive to the wet-level. The major player in the low speed circuit is of course the transfer port, but another big player is the emulsion tube, inside the lowspeed circuit. This tube sits in the idle-well, a vertical tunnel in the carb, that begins in the bottom of the float bowl and ends at the idle-air bleed. This air-bleed allows air to enter the tube and be mixed with the fuel that is on it's way to the transfer port, thru a series of tiny holes the breaks up the liquid fuel into a frothy mess called an emulsion.This is very important; to have this emulsion.
At very low rpm and very low throttle settings, only a tiny amount of oxygen makes it's way into the cylinders. When it gets there, of course it expands to fill the entire cylinder, as the piston is moving down. So now those oxygen molecules are very far apart. Lets say you introduced the proper amount of gas into this chamber now, as one big drop. And then ran the piston up on the compression stroke, and hit it with a spark. There is a very good chance that most of the gas would pass right thru the engine and never lite up. Liquid gasoline is actually pretty hard to lite-up.
So we need to get this gas into a gaseous state and mixed thruout the chamber, so that if has a chance to find oxygen to react with, when the spark occurs. Enter the emulsion tubes.By premixing some air into the gas before it exits the idle well, or as it exits, it is ready to be further smashed as it gets creamed by the air passing between the transfer ports and the butterflys. Here is further mixes. Then it has another 12 to 15inches to get all mixed up on it's way into the cylinder.Next the piston turns around on the compression stroke and this heats it all up and still further gassifies it all. Finally, being nearly fully homogeneous, it is ready to light up, and eventually deliver it;'s energy to the crank.
So as you can imagine, that emulsification step is critical. But how can we ensure it happens properly?
Well, firstly is the fuel level.
The lower it is, the harder it will be for the engine to pull fuel up the pipe, and the easier it will be for it to pull air from the idle air-bleed instead. So to get enough fuel, firsty, the butterflies will need to be higher up the transfers than necessary. And the space between the transfer and the edge of the butterflies becomes wider than necessary, and the fuel does not get smashed correctly. So now the idle quality suffers and you increase the delivery from the mixture screws, which has little to no air in it. So the engine only burns a fraction of the fuel that actually gets into the chamber, the rest just passes on thru, vaporizing in the hot pipes and contributing nothing to the propulsion of the vehicle.
But the higher the fuel level is. the easier it it becomes for the airstream to pull the fuel up, at the expense of pulling in air thru the airbleeds. and so the tendency is to close up the curb idle screws and or the mixture screws. Of course this messes up the emulsion process too.
So I know I harp on this T-port sync a lot, but this is why. The sync and wet-fuel-level are critical for low-speed operation.
So how can you know when the fuel level is correct for your combo? Well this is kindof a guessing game. But I have found one little helper. Actually two. But it always starts with the T-port sync being established. This automatically sorta sets the idle-timing, cuz that is the only way to get a target idle-rpm, after the curb-idle screw is off-limits.
So, here we go
Way #1 is with the engine fully warned up, shut off the fuel supply to the carb. Then wait. One of three things is gonna happen as the engine sips the bowls dry.
1) the rpm will slow down immediately, showing that the fuel level is too low
2) the rpm will immediately start to increase showing that the fuel level is too high.
3) nothing will happen to the idle speed for quite a while, and then the rpm will fall, indicating as at #1. This is the correct, or may be the correct, fuel level. The shorter the delay before falling rpm, the closer to too-low the fuel level is. So now you can make an educated decision on what to do if anything.
Way #2 is to restrict the air entering the engine. First the secondaries must be stopped up to prove they are not sucking air. I just jam a rag in there hard with the engine idling. There should be little to no rpm change, with a 270 cam. If there is more than about 50 rpm change fix it! Close the secondaries up tight but not sticking. You may have a cracking screw that you can adjust, or you will have to bend a link-rod.
Once the secondaries are closed, remove the rag. Then toss it loosely over the primaries. A)If the rpm goes up, then the engine is receiving too much air. Too much air is the same as not enough fuel. So if the sync is set, and the mixture screws are at 1.5 to 1.75, what's left? That's right;fuel level. B) if the rpm goes down, then the engine wants more air, or less fuel; again possibly a wet fuel-level adjustment.
And the third tool, saved for last, to get the rpm down, is the introduction of bypass air. Your 270* cam, should not need any bypass air,but in a 273 it might.I shouldn't mention it but,I have to or this novel I wrote wouldn't be complete.
So, what is bypass air? Bypass air is air we introduce into an engine with a big cam (usually not until 276 or more degrees), to ease the burden of idling. Essentially it is a controlled air-leak. Clean air.The only 4bbls I ever saw with factory bypass air were in the 60s. So if you look at your Eddies, front and center just above the mixture screws, there you will see a casting boss, the remnants of the bypass screw.
The PCV system is a controlled air leak. Later cars with carbon canisters were controlled air leaks. Any air going into the intake that is not controlled by the butterflies is an air-leak. If you control how much air is going in, then it is a controlled air-leak or bypass air.
After the T-port sync is established, there are two ways of altering the idle rpm. #1 is timing. The more you give it the higher the rpm will rise, until it hits a wall and then more advance will slow it down. And vice versa; the less timing the harder it will be to keep the engine running, as the torque falls away, with lower rpm.
#2 is bypass air. But bypass air is waaay less effective.Just a little extra air on a small-cammed engine can make it easier for her to idle, but it will quickly become too much, and the engine will complain about it.The usual way on non-4-corner idle carbs is to drill little holes in the throttle blades up near the transfer slots.Bigger cams like more bypass air. By more I mean maybe one hole in each blade up to about 3/32 each on a 292 cam, in a 360. The size to choose is by experimentation; small cam small holes etc. The smallest holes I ever drilled were 1/16 each.The biggest were 1/8th. Well they were bigger, but I had to close them up,lol.
Ok so one thing to keep in mind is this; increasing timing increases low-rpm torque. While plenty of idle timing is nice to drive on,you have to think about the poor tranny if it slams into gear, and the poor starter trying to fire up the engine when they are both hot, and of course the no-load rpm.
A better solution I have found is play with the rate of advance, as set by the springs and flyweights in the distributor.By using one long-loop spring from an old 318 D, I was able to limit the rate of advance from 2800 on up. Then by installing various lighter springs on the other two studs, I was able to bring the low rpm advance in rather quickly. This gave me the best of both ends; namely a comfortable idle-timing, yet a fast-rate to really blast off with. I have a clutch, and 3.55s so low-rpm timing is somewhat critical. You have a convertor, and so have a lot of flexibility in low rpm timing, unless the TC stalls too low. That could be a sticking point. Unless you have a lot of compression to back that 270 up, I imagine a hi-stall would be the hot ticket. And if I was buying, it would be at least 2800. Then you can let the idle-rpm be whatever.....
Sorry for the long-winded story, but that's me.
Good luck!
