Ignition timing
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Lead Driver
Joined: Aug 2003
Posts: 6,305
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From: Boulder Creek, Ca
Ignition timing
Have basic understanding of ignition system. 65 390ci in a 65 f100. Engine rebuilt approx. 4 yrs ago, .060 over, 4 barrel carb. Just converted from points to electronic ignition. Used 76 f100 w/ 390 as reference for selecting the electronic dizzy, and duraspark module. The spec manual i have only goes up to 74, which list settings for 390 ranging from 10 1/2 and 15 1/2 degrees depending upon dizzy. If set timing at the max. spec of 15 degress, the vac guage is pulling around 15". Not sure if using the vac gauge correctly. Can get about 20" but timing is around 28-30 degrees. If retard to around 18-19", in the range gauge indicates normal, the timing is around 24 to 26 degress. Starts right up at this setting. Seems like quite a descrepancy between spec's and vac gauge, and the 28 degrees awfully high. Not sure if electronic ign. timing on 76 is higher. Does not seem to be over heating this far advanced.
Any suggestions, or information would be appreciated.
thank you,
dave
Any suggestions, or information would be appreciated.
thank you,
dave
Last edited by daveengelson; Jul 12, 2004 at 05:05 PM.
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Joined: Jan 2001
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From: Virginia
Best way to set the timing is by ear. There are too many variables, especially on a motor modified from stock. There is also the possibility the harmonic balancer ring with the timing marks on it has slipped.
If you are curious about the timing marks, you can see if they are right by making a little test jig. Bust the guts out of an old sparkplug and weld a piece of rod sticking out the end.
Make sure the #1 piston is down the hole, and screw the modified sparkplug in the sparkplug hole.
Slowly turn the engine by hand one direction till the #1 piston hits the rod on the sparkplug. Make a mark on the harmonic balancer at this spot.
Slowly turn the engine the opposite direction by hand till the piston hits the rod again. Make another mark on the harmonic balancer.
You will notice the two marks are spaced apart on the balancer. Carefully measure and mark a line exactly between the first two marks. This is TDC 0 degrees of the engine. See how far this mark is off compared to the factory marks.
If you are curious about the timing marks, you can see if they are right by making a little test jig. Bust the guts out of an old sparkplug and weld a piece of rod sticking out the end.
Make sure the #1 piston is down the hole, and screw the modified sparkplug in the sparkplug hole.
Slowly turn the engine by hand one direction till the #1 piston hits the rod on the sparkplug. Make a mark on the harmonic balancer at this spot.
Slowly turn the engine the opposite direction by hand till the piston hits the rod again. Make another mark on the harmonic balancer.
You will notice the two marks are spaced apart on the balancer. Carefully measure and mark a line exactly between the first two marks. This is TDC 0 degrees of the engine. See how far this mark is off compared to the factory marks.
Thread Starter
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Lead Driver
Joined: Aug 2003
Posts: 6,305
Likes: 18
From: Boulder Creek, Ca
Dave, pretty much decided to go with your rec., set at optimum and let it be. The vac gauge starts around 16" until it warms up then stabilizes at around 19", with timing around 26 degress. And yes, am curious about the timing pully. Just came back from infamous test run and seems engine is responding well in all respects. May be different story when try and start in a.m. Thought would measure with piston at TDC then weld rod little longer.
thank you for input,
dave
thank you for input,
dave
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Joined: Jan 2001
Posts: 56,999
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From: Virginia
The only starting problem you may have is on a restart on a hot day. If the timing is too advanced, it will sound as if the battery is dead. Let it cool off, and everything will be fine. If this happens, turn the timing back a little bit. Also what helps this situation is the white wire on the duraspark ignition module. If you wired it up correctly, this wire will have 12 volts on it during cranking. This tells the module to retard the timing a set amount during cranking to make the engine easier to turn over on a hot day.
Thread Starter
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Lead Driver
Joined: Aug 2003
Posts: 6,305
Likes: 18
From: Boulder Creek, Ca
Should be able to test starts on hot days, suppose to get close to 100 degress next couple of days. Have white wire going directly to the ign. side of starter relay, and red to the run, or resistor side of the ignition switch. Seems to be working okay. Did same on other 65 f100 w/ the 302. Both fire right up.
thanks again,
dave
thanks again,
dave
