Comments inside the quote
Soooooo....the kiddo filled up with premium 91 octane Tuesday night..........he claims the ping is gone.....I havent driven the car since so I cannot verify yet......I think he just didnt notice it or look for it in the right time.
The car has been tied up so havent had much tinker time...but we did tinker a bit yesterday.
I hooked up a temporary vacuum gauge in the interior , connected to an extra fitting on the vacuum "tree" on the rearmost intake runner.
It runs a steady 20 in/mg while idling in park or neutral, at about 700-750 rpms.....some very slight "rocking" of the needle...a gentle sway....to 19.5 or so and back to 20 as it idles...but seems pretty steady to me? I agree
Give it a rev and it drops down to like 5 in/Mg but shoots right back up to 20. I think thats normal right? It should shoot back up to about 2 to 5 inches higher than what it typically idles at
In DRIVE its a different story......drops to 15-16 in/Mg at about 550 rpms. The gauge indicates that is "late ignition timing". Don't pay too much attention to the wording on the face of the gauge;it's the numbers that are telling a story, that we have to interpret.
As I recall we have it set a few degrees above the stock setting per the emissions sticker....I think we have it at 13 or 14....versus 12 for stock....but I may be wrong there, will have to recheck. And this was done with the vacuum advance disconnected,right
I also tried applying vacuum to the distributor vac advance......it changes the idle just barely noticeable (increases a TINY bit)....using 20-25 in/Mg using my mighty mite vac gun. Dont know what it did to the timing now that I think about it....I guess I should have checked that.That would have been a good thing to do. But if it was working right, wouldn't it advance more and therefore raise the idle more? yes it should, if it is working, and if you set the timing properly with the vacuum advance disconnected.Put the vacuum gauge on the spark port and make sure it is dead, showing zero or very close to zero vacuum.
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All the idle-timings have to be set with the
vacuum advance disconnected.
Scenario 1)
If the sparkport is active at idle, and if,say, it brings in 9 degrees, then you set the idle timing to 14*@750. Now when you put it into gear, the convertor drags the idle speed down and the vacuum falls. So some of that 9 degrees drops out, and the result is a 550 idle at some reduced vacuum, and the final gauge reading is 15/16 inches. Then you come along and apply the mighty-vac restoring the 9 degrees. But since only 2 or 3 or 4 degrees dropped out, now, those few degrees is not sufficient to increase the idle rpm very much. That is one scenario, and the one I might favor.
Scenario 2) Here is another;
The idle rpm was too high at the time of the timing check. The transfers were very active, and perhaps the sparkport was already pulling.The active sparkport was pulling timing in. The fat transfers were compensated for by screwing in the mixture screws. Now it idles very nicely. Now you put it into gear. The TC drags the idlespeed down. Some V-can timing drops out. And with the now too-lean mixture the idle speed drops yet further. Again applying vacuum to the can is not sufficient to bring the idle speed up much.
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The cure for this knowledge.
A)You need to know exactly what your timings are doing at all times, and you need to know that
B)the throttle blade is correctly staged. This staging is very important.1) The V-can needs to come in when it is told to,and not before,and 2) The balance between the transfers and the idle discharge ports has to be very finely set.
>As to A) The idle timing can be anything that the engine likes. BUT,if the engine likes 20* at 650 idle, but only likes 8 at 800,at tip-in,then you have a decision to make. Common sense has to rule. Also The POWER timing has to be determined very early in the tune, and whatever you do at idle, will alter the power-timing, so you have to keep that in mind. The vacuum advance must not be allowed to interfere with these two parameters,namely the idle and power timings. So the best way I have found is to make a graph of what the timing is doing.(Directions to follow).
>As to B) Staging the throttle blade(s) is called setting the the T-port sync, which is short for transfer port synchronization. At idle the sync can be way out, and adjusting the mixture screws can in most cases compensate for it. But the millisecond you open the throttle, the mixture goes off-track.
There are a couple of ways to get the sync close but only one right way. I'll only tell you about the right way. The right way is to take the carb off and flip it upside down. Make sure the throttle is on the curb-idle screw. Then go find the transfer slots. They are on the leading edge of the blades, one in each hole, and right beside the mixture screw discharge holes. From the underside, on the curb-idle screw, these slots should appear as little squares. Make them so,with the curb-idle speed screw. They can be slightly taller than wide, but not the other way. Now go find the sparkport. It should be on the top side of the blade, and hopefully slightly above it. It will usually be close to the transfer slot, and usually 5* to 10* towards the outboard of it, and on the top side of the blade. It may be a hole or a short horizontal slot. If you find it in the "correct" location,check that the base gasket properly closes all access to the intake except those it is specifically designed to not close, and put the carb back on. Reset the mixture screws to 2.5 turns out from lightly seated. Now this is very important; do not readjust the speed screw from this point until all other avenues (which I am going to give you next) have been explored. Ok then put it all back together.
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> Put a vacuum gauge on the spark port. Start her up and warm her up on the fast-idle cam.Take a reading on the spark port, and compare it to straight manifold vacuum. It should be close to the same, perhaps slightly lower;maybe 2 inches or so,no big deal.
> when she is warm tap her down onto the curb-idle screw. If the idle speed is not close to where it should be,
DO NOT USE the curb idle screw to adjust it. You will adjust the speed with timing and idle air bypass, with possibly a fuel level change. Do not mess with the mixture screws at this time. Do not mess with them until the idle speed has dropped to 750 or less.
>Check the vacuum on the sparkport; it should be zero or very close to it. If it is over 5 inches, reduce the curb idle speed until it is; up to 2 turns and then;leave that screw alone from now on.
If it is zero, and the idle rpm is below 650N crank the speed screw in up to 2 turns or until the sparkport reads a maximum of 2 inches,and then leave that screw alone from now on. Now you can reset the mixture screws
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>Now if the idle rpm is still too fast, go look for too much timing or an air leak.If it is too slow, scroll down to page 5
Step 1)
Retard the timing until the Idle rpm is 750N or less. Do not pay attention to what it is at this time, just retard it. Now go put it into gear. Expect a 50 to 100 rpm drop,with the vacuum dropping only slightly,maybe 2 inches and a nice stable idle.
You may tinker with the mixture screws.
But if the timing by itself is not sufficient to bring the speed down, or if the timing has to be retarded to say less than 6 degrees, then;
Step 2) we will have to look for a vacuum leak. First check all vacuum devices attached to the carb or the manifold. The test is by pinching the hoses, fully closed, and waiting for the speed to stabilize.Check the brake booster,the choke pull off,the vacuum amplifier,etc.; check all vacuum taps. The sparkport should still have the gauge on it. The PCV is tricky. Slowly pinch it closed and see what happens.The Rpm should fall continuously, and end up slow enough to stall the engine. If it doesn't, you will need to check the intake manifold to head interface. Remove the vacuum gauge from the sparkport and plug the port. Plumb the gauge to the manifold and lay it on the intake somewhere where you can see it. Then spray water from a Windex bottle, all along the interface while watching the gauge. The needle should not be affected in the least. Spray the tops and sides, then try to hit the undersides as well. No change in idle speed or vacuum reading means the intake is tight, and we have proved that the high idle is not from an air leak.
> So if the IDLE speed is still greater than 750 with the timing at 6*, and with no vacuum leaks,and with the Tport synced within 1 or 2 turns from square; Yours will be the first one for me. And I am stumped
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But
far more likely will be that the idle speed will be too slow. In this case we will bring it up with timing and idle air bypass.
step 1) crank the timing up until the rpm stops rising, read the timing and write it down. Then retard the timing until the rpm falls below 650 or 6 degrees is seen. Write the degrees down for 650rpm. That is your idle timing range. It will probably fall in the 6 to 20 degree window,so set it at 12 to 14 for now(how convenient,eh).
So now you say the the idle speed is still too slow? Ok clamp the PCV hose closed and pull it off the valve. Cover the end with your thumb and remove the clamp. Slowly introduce air into that hose by sliding your thumb off the hose. Sooner or later, the idle rpm will be just right. It is your job now to introduce air into the intake, equal to whatever it took to achieve that perfect idle speed, less what the PCV is currently giving. How you do that is up to you. Here is how others have done it; drill holes in the butterflies, run a continuous crankcase draw into the intake, swap out PCVs until you luck into the right one, drill a hole in the PCV valve above the orifice, Tee into the PCV line and introduce air there from the air cleaner house or the air horn area, etc. The most common method is to drill the butterflies. Buuuuuut Hold on for a bit. Put the hose back on.
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Now we have reached a point where we need to get after the power-timing first, and especially the part throttle timing which seems to be giving you fits. If we drill holes now for the perfect idle speed, at 12/14 degrees, but we later find that 12/14 is too much, then we end up having to fill those holes and redrill them to a smaller size. That sounds like doing things twice, which I'm not a fan of. So if the engine will stay running in gear, and idle at 500/550; take a break. If it does not stay running at that speed, crank in some curb-idle, but
COUNT THE TURNS AND WRITE IT DOWN, we will need to return to that later.
> Ok so Lets figure out the detonation free power timing first. Rev her up until the timing stops advancing. Grab the rpm and the amount and drop the Rs back to idle. Record your findings . Hopefully the timing stopped advancing at or before 3600 or close to it, and the amount was 36* or less. If it did, that's great. At this point we are right back where we started right? The idle timing is 12/14 where we started, and the idle speed has been dinked back and forth but it is back where we started. The only thing different is the vacuum advance has been disconnected and the port has been plugged. That is how this game called tuning, is played. The engine is telling us what it doesn't like, and we fix it.
>so now comes the roadtest. We are only concerned with WOT timing right now. And we only want to give her as much as she asks for and no more . So take her out in first gear accelerating moderately until you hit 2800 rpm, and then roll into it harder, listening for the tell-tale marbles-in-a-can rattle. If you
don't hear it by 3200 or so, slam the pedal down,and continue until the rpm of peak advance, previously recorded or 4000rpm, that is enough Rs. Ok stop the car. Recheck the power-timing. If it is less than 36*, make it so, and another road test. No detonation is what you are looking for.If you hear it after 3200 stop! Put it back 2* and another road test. Continue in this way until you find a power timing that does not produce any detonation over 3200rpm. Write it down.Label it maximum.This will be your maximum power timing, and must not be exceeded.
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>Now check the idle timing. If it is less than 10 or more than 20 this is not so good. If it is 12/14, it is perfect. From 12/14 to 20 we will see.
Now another roadtest; this time looking for detonation between idle and 3200, at various throttle settings; still with the vacuum advance disconnected,and the port plugged. Plumb the vacuum gauge to the intake with a long enough hose that you can see the gauge from inside the car. If or when you hear detonation, write down the vacuum reading and the rpm. The vacuum gauge will be your load meter, telling you in a repeatable way when and how the rattle is occuring. What you can do on the roadtest is to slam the pedal down until you see 10 inches vacuum and let the car accelerate to 3200rpm while continuously adjusting the vacuum gauge with the foot-feeder,to try and maintain the 10 inches. If no rattle is heard, you repeat the test ,this time at 8 inches or 6 inches, and so on until you hear the death rattle. If the rattle occurs at a particular rpm or small range of rpms, this is what we need to know. And you can run through this specific area multiple times with various load settings.
> now comes the graphing I earlier mentioned. Go home put the timing lite on it. Rev it up to the point detonation was occurring, and read the timing. Read it on the even number rpm such as 2400. Write it down. Then check the timing 200 rpm higher and two hundred rpm lower, write those down. And go 400 below/above the rattle and write those down too. Now,I like to dig out a piece of graphpaper and plot these points on a graph with rpm across the bottom and advance up the left side. I put the numbers on there and circle the points of detonation. These points will have to be reduced.
So if you previously did get rattle on PT (part-throttle), reduce the idle timing 4 degrees and repeat the test. If no rattle is heard, put 2 degrees back in. If still no rattle,great!, but if rattles now ,go back 2 degrees on the idle timing. and so on. When you find an idle-timing that does not produce any rattle, stop. Read the timing in the previously troubled area. On the graph write in the trouble free timings underneath the previously bad and circled numbers.
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> Now we are gonna have to marry your idle-timing to your power-timing with respect to achieving the trouble free PT timing numbers. At this point, with the idle-timing set to achieve a no rattle in the troubled-zone, I would read and plot all the rest of the timing numbers every 200 rpm and flush out the graph all the way out to the point of maximum advance previously established, and all the way back to idlespeed. This will be representing your current timing system, which is detonation free. Notice that the power timing number is less than what we previously established as the maximum. Go find that number and put it on the graph. Also,at or near 800rpm circle the highest idle timing you find there. Now with a different colored pen,connect that @800 number to the detonation free-zone, and connect that zone up to the maximum power-timing number previously established. This new colored line is the one you are gonna have to build.
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> But wait, we can do more. There is a distinct possibility that below the troubled zone, more timing could be advantageous, right? So with that in mind, lets perform a stall test with the idea that more timing can be used at take off. So warm up the engine. Lets do a stall test. The only thing we are concerned about is to see what the rpm will be, at the instant the car begins to move. Oh and we don't want to run over anything or anybody. So lightly apply the brakes,put in in low,and get eyes on the tach. Then smack the gas pedal down about 1/2 way, and record the maximum rpm on the tach. Let the car move ahead slightly by easing off the brakepedal. Repeat about 3 times and average the numbers. Then for good measure slam the gaspedal down harder and grab that number. Do not let the car travel further than a few feet to a carlength.Record the number.
If you get something like 1800 rpm or higher, great. If it is less than 1400 you will have to replace it, it does not like your cam/compression or it is failing. If it is higher than 2200 double great. If it is between 1400 and 1800, the bottom end may be soft, and then it is up to you if you can live with it. But the only thing I want to know is; what is that flash-rpm and does it rattle? With no rattle, crank up the Idle timing, and try it again, as before,no brakes, drive up to the trouble zone, stopping short of that. Repeat this until you get to 20* idle timing, or until you get rattle. Then if it rattles, back up the timing two degrees. Now stop the car.Check the timing every 200 rpm from 800 to the troubled zone, and transfer the numbers to the graph. Get a third colored pencil and connect the dots but do not connect this line to the troubled zone. This is the theoretical maximum lowspeed timing.
Now the marriage begins......... Below the stall speed we can do anything we want to, so long as it makes the engine happy
.
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> So the first thing we do is straighten the line. It is hardly likely that we can hit all the points with the factory dizzy. So With a pencil now, Take two or three points centered around 3600 and draw a straight line thru them, running the line up to 4000 and down to 2800 in that same straight line. Now pick a point centered in the troubled zone and draw a straight line connecting as many points as you can in that troubled zone. Let the left end fall where it may, and stop at around 800 rpm. This will be your target timing curve.
> The first thing we will want to know is, what the curve will deliver at idle. If it is up at 12/14 that's great!, But more likely the curve will drop in closer to 8*. Had we earlier drilled holes in the butterflies for the perfect idle speed and the timing at 12/14, then those holes would have been too small. That would have been a good thing. But if the curve now dictates 20* of idle timing, then those holes would have been too large.
>Then the second thing we need to do is marry the max power timing number to the idle timing number. For instance if the max number is 36 degrees and the idle timing is 14 degrees, then this is called 36-14= 22* in the dizzy. If you have that or close to it we are in good shape. Then we just have to modify the springs to achieve the curve.But if your Dizzy does not have a range that you need, then we have to make it so.The slanty range is often considerably larger to accommodate the low spec idle-timing and yet generate enough power timing.Modification is by stripping the dizzy down and limiting the flyweight travel.
This may sound like a lotta work, but every hot-rodder who ever lived either had to go thru this, or his combo was never optimized.
Once the flyweight cam has been limited, then,the curb idle speed can be slowed down by the exact number of turns you previously cranked it up by, (you did right it down right?) ,and the power timing cranked up to whatever you previously established as "maximum",and the bypass air can be added. If you did it right,the idle timing will now match the graph.
> If the curve has a kink in it;
And the very first curve you made also has a kink in it, then we are in good shape.
>But if the target curve is more or less a straight line;
then we may have to get a spring kit.
At this point all we have to do is slow the curve down to match the graph.This is done by mixing and matching springs or lightening up the flyweights until you get a match to the graph or at least the "pinging" goes away,lol. Building a match to the graph is a worthy endeavor, but many times it is either impossible, or the hours just take too long. Most times we just try to hit the most often used bases, like WOT, and freedom from ping at PT. You just do the best you can with the parts we have, in the time the customer is willing to allocate to the job. So I wish you all the best.
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Now I might as well tell you;
We are doing all this work with 91 in the tank.
If you switch to another grade gas, you get to do it all over.
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And we still have not looked at the vacuum advance. We cannot do that until the centrifugal is set.
to be continued
