Ping/detonation?
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Ping/detonation?
Guys,
I have a rebuilt 1969 lincoln 460 block with 73 heads in my 1986 f250. compression is about 9.5-1 I am getting a ping/detonation at 2000 rpm with part throttle application on hills. When throttle opened up more rattle goes away. I have retarded the timing (6 degree initial, 32 total). I have an Edelbrock 1411 750 cfm carb (This model is for gas milage not hi-po)which I have installed the stiffest step up spring and gone up 2 metering rods (+8% rich) on both cruise and power mode. Still have a ping. This tank of gas I used 89oct and added oct boost (oct 104 brand). Is the octane the issue? Too lean? (Plugs have a light tan color) What is the minimum timing adv I could get away with. The motor has maybe 300 miles on itand I really don't want to hurt it Any knowledgable comment would be appreciated. Thanks.
I have a rebuilt 1969 lincoln 460 block with 73 heads in my 1986 f250. compression is about 9.5-1 I am getting a ping/detonation at 2000 rpm with part throttle application on hills. When throttle opened up more rattle goes away. I have retarded the timing (6 degree initial, 32 total). I have an Edelbrock 1411 750 cfm carb (This model is for gas milage not hi-po)which I have installed the stiffest step up spring and gone up 2 metering rods (+8% rich) on both cruise and power mode. Still have a ping. This tank of gas I used 89oct and added oct boost (oct 104 brand). Is the octane the issue? Too lean? (Plugs have a light tan color) What is the minimum timing adv I could get away with. The motor has maybe 300 miles on itand I really don't want to hurt it Any knowledgable comment would be appreciated. Thanks.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Yes, you adjust it by inserting an Allen wrench into the vacuum port of the advance can. I can't remember the size off the top of my head. If memory serves me correctly, clockwise gives more advance and counter-clockwise gives less advance.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Since you are getting pinging, that means your timing is over-advanced. I would try backing it out a half-turn at a time until the pinging goes away. Have you tried richer jets in the carb too? Basically anything that causes the air\fuel to ignite before the piston is close to top dead center causes pinging. That can be overly advanced timing, high compression with too low octane, or overly hot combustion chamber temperature which is caused by a lean condition. Since you seem to have a handle on most of that stuff, the timing is what I would try but now that I re-read your post I didn't see anything about jets.
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I haven't tried jets yet just the metering rods and step up spring. Would you recomment one size at a time or a couple? Thanks again.
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From: Virginia
I too think it's the timing, and the vacuum advance would be the thing to check first. If you want a quick check, just unplug it, and try and see if it will ping. If it goes away, you know that 10 degrees added in is just a little bit too much.
The reason I think it's the vacuum advance, is because you said when you go ahead and push the gas pedal down, it goes away. When you are doing this, you are reducing the vacuum the engine produces, then the vacuum advance is relaxing and reducing the timing.
The reason I think it's the vacuum advance, is because you said when you go ahead and push the gas pedal down, it goes away. When you are doing this, you are reducing the vacuum the engine produces, then the vacuum advance is relaxing and reducing the timing.
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I tried disconnecting and capping off the line from the vacuum adv and shore nuff ping/rattle went away. Adjusted the screw in vacuum can ccw one full turn and it helped some. Reduced initial timing even more to around 4 degrees and the combination appeared to do the trick. No Ping. It was cool out today so I guess the real test will be when it gets hot out. Looked at a spark plug and it was a nice light brown. Crossing my fingers but with you guy's help I think this issue may be behind me. Thanks a bunch!
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