4.9 bored over
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From: Western Washington
4.9 bored over
I have a reman 4.9 in a 1974 F-250 that I have been working on for the past few months. I have been having trouble getting it running consistantly and can not figure out why. I pulled the plugs to check for fouling and looked at the Piston through the hole with a light and noticed a ".040" on top and I'm guessing that means it is bored over .040??
If so would that change things like spark plug gap, points gap, or timing? I have set everything to factory specs and I am starting to think that's my problem. It bogs and bucks when I try to accelerate especially in 2nd gear. after some research it seemed like possible spark knock so I set the timing at 6 btdc and it helped some but did not cure it I was wondering if any one here would know more than I can find anywhere.
Thank y'all in advance Hopefully someone has some info!
If so would that change things like spark plug gap, points gap, or timing? I have set everything to factory specs and I am starting to think that's my problem. It bogs and bucks when I try to accelerate especially in 2nd gear. after some research it seemed like possible spark knock so I set the timing at 6 btdc and it helped some but did not cure it I was wondering if any one here would know more than I can find anywhere.
Thank y'all in advance Hopefully someone has some info!
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Joined: Apr 2004
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The .040 over won't change anything.
What transmission, what gears, what tire and what speed are you trying to accelerate from in 2nd?
Have you gone through the carb and adjusted it to spec?
What ignition do you have?
What transmission, what gears, what tire and what speed are you trying to accelerate from in 2nd?
Have you gone through the carb and adjusted it to spec?
What ignition do you have?
Thread Starter
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New User
Joined: Apr 2019
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From: Western Washington
It has a new points distributor and a newer coil
Tuned
Joined: May 2013
Posts: 396
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From: Ottawa, Canada
6 degress of timing is a bit low. I think the factory on my 85 is 10 degrees. If its bored 0.040 it won't make a difference other than its now a 306 cubic inch engine. I'd look for carburetor problems, vacuum leaks, poor wiring and grounds.
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From: Western Washington
I finally got it smoothed out after a LOT of trial and error I narrowed it down to a breathing problem. I changed the pcv valve on the front of the valve cover and now the problem goes away once it's warmed up. It still has a little problem with vacuum and I think it's my whistling brake booster but it runs and drives good now. Thanks everyone for the info!
