Also, the tried and true method of static initial setting works very well. Then rev the engine and watch to ensure that this vacuum, as well as mechanical advance. Set the called for engine rpm, use your strobe timing light, and get the pointer to indicate midway between the two balls on the harmonic balancer. First, clean the points, filing only if necessary. Since it is combined with centrifugal advance, but is a set amount of advance (20* in this case IIRC), there is going to be some problem RPM that limits how much total vacuum advance you can have.ĭespite "Common Knowledge" about plugging and disconnecting vacuum from engine to your distributor, both your manual, as well as w the one for my 1954 Cadillac, make no mention of disconnecting, and are in fact steel, rather than rubber hose lines. Just like centrifugal advance, too much vacuum advance will make the engine ping, rattle, or try to kick back on itself. This is what vacuum advance is for, additional advance for part throttle operation. There is no vacuum at full throttle, so no vacuum advance.Īt part throttle, the fuel charges burn slower, and the engine would like the fuel lit sooner to get the maximum good out of it. Ideally, the centrifugal advance should track what the engine wants for maximum power at full throttle at any RPM. If less timing makes it smooth out, too much timing (at that particular speed and load) is probably the issue. It might detonate, ping, or just try to kick back on some firing impulses. If it should go too far for the compression, or the fuel, or the engine speed, or just too early altogether (piston isn't all the way up when the pressure wave hits) the engine will rattle or run rough. If it is way off, distributor work is necessary to correct. If it is wrong at the high end, and you reset it so it is right, it will be wrong at the low end. You can't compensate by just setting the timing if it is wrong at high RPM, at least no more than a couple of degrees. Make a real quick check and let it back down. Then you can see advance with a regular timing light (no dialback).Īs mentioned by Joe, the best way is a distributor machine, but not many people have those.ĭon't hold it at 3700rpm all day with no load on the engine. MSD makes a kit with a bunch of different sizes. The tape has to be the right diameter for the crank pulley or harmonic balancer. Subtract your second number from the first. Now run the RPM up to the same level without vacuum. OR- To check vacuum you could pull a bunch of vaccuum at idle with your pump and see how much the timing changes. Should add about 20 degrees to your reading in this case. To check vacuum, you would make a second run with a hand vacuum pump and put a whole bunch of vacuum on the vacuum advance. More likely you would use the buttons on the dialback timing light to line the mark up to TDC, and then read the actual number afterward off of the timing light. Vacuum should be disconnected and plugged. To check total you would add the initial timing (whatever it is currently set to, as checked with your light) to the 30 degrees, and check that at 3700rpm. You CAN do this on the engine, but it requires a degreed balancer or a dial-back timing light to check performance. If mods to the engine or the use of less-than-optimum octane fuel require changes to the advance curve, your best bet is to do this on a distributor machine. You don't adjust this out, you fix the worn parts. Note that any wear in the distributor bushings, advance weights, or timing chain will alter total timing. If the distributor is in good shape, the total timing will match that factory spec (within manufacturing tolerances). You set the INITIAL timing per the service manual. Normally this is set at the factory when the distributor is built and is not changed in the field unless you have modified the car and need a different advance curve. You "set" total advance by modifying the springs and stops on the centrifugal advance weights in the distributor. So my main question is that to set the total advance.should I rev the engine to 3700 rpm, set the timing light to 30* and then turn the distributor so that the pointer is between the two tabs on the balancer?
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