timing adjustment question 390fe
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timing adjustment question 390fe
i own a 1976 f250 custom with a 390 4v engine. when i bought it, all the smog equipment and the oil bath air filter was taken off and replaced with edlebrock air filter. i was led to believe that with out the smog parts it would breath easier and should be retarded more than the specs called for. prior to being told that my friend had it hooked up to a timing light and found that they had advanced it quite a bit. he said that was why i was burning through spark plugs. so we set it back to the stock setting, and now im wondering if i should retard it further. any suggestions would b great. oh and i dont know if it will make a difference but it has a 4bbl holley and dual pipes.
Lead Driver
Joined: Jan 2003
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From: Ohio
Welcome to the board.
Timing? Stock was probably about 6 degrees? Depending on condition of motor, quality of fuel and how you drive it you can probably move it up to 10-12 degrees. It will really perk up the low end grunt. The smog equipment does not really affect what the timing should be now(in basic terms). I'm not really sure what those trucks had on them? Probably some kind of timing retard control on dizzy, air pump, EGR?
What do the plugs look like? Black, sooty? That is carb issue, and needs addressed. Which carb? Numbers on the air horn will tell us exactly what it is.
Timing? Stock was probably about 6 degrees? Depending on condition of motor, quality of fuel and how you drive it you can probably move it up to 10-12 degrees. It will really perk up the low end grunt. The smog equipment does not really affect what the timing should be now(in basic terms). I'm not really sure what those trucks had on them? Probably some kind of timing retard control on dizzy, air pump, EGR?
What do the plugs look like? Black, sooty? That is carb issue, and needs addressed. Which carb? Numbers on the air horn will tell us exactly what it is.
Post Fiend
Joined: Apr 2008
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From: Big Sky Country
My 390 loves 12 degrees btdc, you can run more initial depending on where your mechanical is set but i wouldn't recommend it.
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If they removed the EGR, it can be prone to pinging more at light-to-mid throttle.
If it's not pinging, don't worry about it.
The rest of the "pollution stuff" back then was air-injection (doesn't do anything to the way the engine runs), some funky timing advance setups (more for cold start than emissions), and that's about it.
If it's not pinging, don't worry about it.
The rest of the "pollution stuff" back then was air-injection (doesn't do anything to the way the engine runs), some funky timing advance setups (more for cold start than emissions), and that's about it.
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i dont have the numbers in front of me and its raining like hell out but i know that the carb is a holley 4bbl. im going to have to go over to my buddies to check on the plugs but when i went into my haynes book and looked in the back, they look like the WORN plugs. electrodes were gone. i have adjusted the carbs, their was way to much fuel in the bowls, took the screw out to check the levels and it came pouring out. also, i talked to my buddy, and apparently he neglected to remove and block off the vacuum hose. figures, never trust a self proclaimed chevy man around a real truck. ill have to do the timing over again. i have the sticker with the specs still on the valve cover but its really not legible at this point so thanks for the info guys
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I've always set mine by the pinging.....just advance it until it pings and retard it just a bit. Different fuels and setups on your engine make it so no one setting is perfect...advancing it till it pings and then back off slightly and it's perfect for your setup, fuel, and driving style.
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I've always set mine by the pinging.....just advance it until it pings and retard it just a bit. Different fuels and setups on your engine make it so no one setting is perfect...advancing it till it pings and then back off slightly and it's perfect for your setup, fuel, and driving style.
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Actually, accelerating by lightly pressing on the throttle while already moving, say from 40 or 50mph, or adding a little power when pulling a hill seems to always be the limiting factor. Occassionally the starter kicking back would be the limiting factor. You can't hear the pinging at full throttle, at least as loud as my exhaust always is!! But you are correct, not at idle, it must be done while driving.
Post Fiend
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Actually, accelerating by lightly pressing on the throttle while already moving, say from 40 or 50mph, or adding a little power when pulling a hill seems to always be the limiting factor. Occassionally the starter kicking back would be the limiting factor. You can't hear the pinging at full throttle, at least as loud as my exhaust always is!! But you are correct, not at idle, it must be done while driving.
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