Because the burn requires a fixed time, spark must start earlier as engine speed increases due to less available combustion time. It seems like it runs worse through the rpm range. No vac at idle, so you can set your initial timing and idle speed without any vac intterference. All of them have an adjusting screw inside the vacuum canister. You will be rewarded with excellent throttle response and a clean buring engine. No noticeable difference in running between the two cars, but then the '71 and '69 dizzys may be different. Each provided a specific amount of spark lead—usually 20 to 25 degrees—with unique vacuum activation points.
It would have been on the top of the front carb, located similar to where the vacant threaded hole is on your rear carb. Both types are controlled in the throttle position and provide an accurate determination of the engine load. I am sure there have been some changes due to the engine change out and I am not sure whether or not the new brake system has anything to do with it. Is the application for street car automatic or 4 speed car? And connecting a line to each venturi vacuum takeoff of a dual set up will not increase the vacuum---such a practice is just a waste of copper tubing. I've looked at my own dissassembly photos, Moss, Bently, Hayes, and Closanger. I like High Static timing, it works best with mech totaling out.
One big variable is how much distributor advance you are running and how much initial. It is only active when the rpms are below 1100 and it was more or less a concession to emission requirements. The result included a strong, stable idle and seamless transitions without any effect on economy. Although Holley employees will take part in answering questions from time to time, your questions may or may not be answered by Holley personnel. I also agree the vacuum advance is a worthwhile feature. Once installed and connected to manifold vacuum, idle speed increased as soon as the engine fired. What we did discover, though, was a smoother transition when reapplying the throttle after coasting at speed, likely caused by the spark lead that manifold vacuum advance maintains while coasting and decelerating.
A few pumps of a manually operated vacuum tester should provide a full advance, and the sliding plate should stay in place until you remove the vacuum from the port. Once the base timing is set to the correct position, you can connect a hand-operated vacuum pump to the diaphragm, give it a few pumps, and then watch the timing mark on the crankshaft harmonic balancer advance on the timing scale with the timing light. When you rev it through the gears, it continues to misfire, and barely pulls at all. Remember the guy that gets the most work done with the least amount of timing is better off. I've continued tweaking my tune to see if I can get better performance or mileage out of this. Then you click on Private Messages to read my reply.
This way there is no effect on the initial timing setting. Ken - yes you make a fair point! There is no venturi vacuum available to advance the spark as the speed picks up and it remains retarded until the throttle is let up. Driveability or maximum racing power. It would help to know just what distributor you have, too, of course. After the preliminary adjustments, idle quality noticeably improved, and vacuum jumped roughly 1. I've built a zillion combos over the years and they all wanted something a little different in the ignition curve.
Plus that tubing can easily bend and break leading to it getting pitched out. I tried attaching the hose there. Hose coming off vacuum advance assy. But on the road at moderate acceleration it will stumble and buck, then go. These are several open ports on switched that are not being used. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. Subsequent road tests proved that the engine was largely unaffected by clutch engagement, and acceleration was extremely smooth and effortless.
The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance 10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance at steady-state cruise it only takes about 40 horsepower to cruise at 50mph. Nail the throttle and that extra 20º timing drops away and a bog will probably occur. Sorry but this is what I was told. . I have work to do this weekend Under light-load conditions small throttle opening, high manifold vacuum you have a slower-burning, leaner mixture so starting the ignition burn sooner allows all the fuel to ignite.
The exhaust pipes seem to be very black and sooty, but the plugs appear normal Given the above, do you have any suggestions as to what it could be? To accomplish this, a load-sensing device is mounted to the distributor body. Well informed engineers wish that the problem really was that simple. Vacuum hose coming from vacuum advance will not reach. I know on my '99 Z28 that at about 50mph while under light throttle it will register pinging on the Knock Sensor and it's only pulling about 24 degrees of advance at that point. Just remember, that any given way of doing the - 1. I'd have to look to see what the distributor is on the 71 engine, but it's 5 miles away. If you take it at the manifold, just make sure you disconnect and plug the port when timing the engine.
Ported Vacuum advance is for cruising around at partial throttle settings where maximum economy is important as throttled operation has a less dense mixture that takes longer to burn, hence the extra timing from the vacuum advance. In the back of the intake where the brake booster will be hooked up to? The motor would be pretty sluggish without any type of advance other than initial. Even adding a few degrees at part throttle will improve mileage and responsiveness. As an engine revs up, we need to allow even more of a head start for the spark plug in order for complete combustion to occur. I think the same way- especially after reading this artical. Is it the yellow-arrowed nipple by chance? This is mainly to improve fuel economy at steady-state speeds when you are getting far less than optimal cylinder filling due to a mostly-closed throttle plate.
But Please explain your knowledge so this orginal question can be answered for him. Basically, engines require some means of advancing spark timing as rpm increases since the pistons, in effect, try to get ahead of the burning speed of fuel charges. Now, switch the vacuum advance to a direct source of vacuum and again check the idle rpm? Low cylinder pressure engines typically like lots of advance at idle and light throttle to make them responsive. Here is a close up of the mechanical advance system. Thanks for the photo and advice.