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The Accel #31035, #31035 Instructions is an adjustable vacuum advance can for GM HEI that is said to allow infinite adjustment to both the amount and rate of advance. If the vacuum advance you have comes in OK but gives too much advance, you will need to physically limit the vacuum advance can's travel w/a vacuum advance limiter plate like the Crane #99619-1, #99619 Instructions.Ĭrane has an adjustable vacuum advance can kit- Crane #99600-1, #99600-1 Instructions. After getting the static timing pointed to No 1 and close enough to get th engine running I timed it at around 12 degrees using a Gunsons advanced timing light. Using the vacuum advance should help bring up the idle vacuum as well. You may well need an adjustable vacuum advance to get the advance at a low enough vacuum, given the lack of idle vacuum you now have. If the blades are opened too far, the idle quality and off idle response will not be good. This will help keep the carb primary blades from being opened too far to get the idle speed where it needs to be. It should be limited to around 10° of added advance. I would recommend that you use the vacuum advance, hooked to manifold vacuum. HERE'S an exploded view of an HEI distributor. If you use a mechanical advance, be sure the advance plate is free to move, w/o binding or friction. The problem is if you have a different diameter damper than what the timing tape is made for. Timing advance means that the spark plugs are firing earlier in the compression stroke. Spark plugs need to fire at the right time, which can be achieved by advancing or retarding the timing of the engine. The way we do it is to set the timing at 30 degrees total. Ignition timing is measured in degrees of a crankshaft rotation before top dead center (BDTC). You can also buy a timing tape, they're not very expensive. When the engine is together and running, we like to check the distributor to see if each cylinder has the same amount of ignition timing. MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You should verify that what you are seeing at the damper and timing tab for TDC is actually TDC.ĭETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC. Using a Timing Light: A timing light is a handy tool for checking and adjusting ignition timing.
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