new motor backfires
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Senior User
Joined: Nov 2004
Posts: 131
Likes: 1
From: springstead
new motor backfires
i just built up my 351m and put a new cam, the summit 5200, and edelbrock intake and a rebuild carter afb, all done by myself. it is also bored out .030, high volume oil pump, heads surfaced and redone. yadayada. my question is to you is the timing and the backfiring. i ran my timing straight up, 0 degrees, and i timed it to 0. its always backfires, sputters and then quits. so i figured its the bigger cam and i advanced it 10 degrees and still did it, advanced it to about 18 and it doesnt do it as bad as before. i am just wondering what the problem might be.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Backfire can mean mixture problems. Exhaust backfire is usually from unburned fuel in the exhaust which is ignited by a hot exhaust valve. Intake bakefire can be from too rich or too lean mixture.
So before you go ripping the motor apart looking for timing problems, check your carb for flooding or vacuum leaks.
So before you go ripping the motor apart looking for timing problems, check your carb for flooding or vacuum leaks.
Junior User
Joined: Nov 2003
Posts: 58
Likes: 0
From: saint petersburg,florida
Backfire problem too.
I have a 400 bored .060 over with 265 cam-edelbrock 650w/weiand dual plane manifold,new timing chain 0 straight up,headers and ford ignition. I took compression test, checked plug wires etc.
I have the same backfire problem. I also need help but will advise if I get it figured out.
Thanks,Seneca
I have the same backfire problem. I also need help but will advise if I get it figured out.
Thanks,Seneca
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Elder User
Joined: Jan 2004
Posts: 867
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From: Eastern Pa
Always start with the easiest and overlooked. I would check wires for right order and cracks. Next check for vacuum leaks using carb cleaner or starter fluid. Next if you can run it long enough to get a read pull the plugs and see if they are soaked or white. This could tell you if it's a fuel problem. Then your cap and rotor. If all the easy externals check out then you may have to look deeper like the valve train geometry.
Junior User
Joined: Nov 2003
Posts: 58
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From: saint petersburg,florida
[B]Using a straight edge across the top of the head when at top dead center I scribed a mark across each pushrod and turned the ingine over until the pushrod was at dead bottom.
I then scribed each one once again. The difference was .040. I was told to do this by the shop that sold me the pushrods and lifters.
Seneca
I then scribed each one once again. The difference was .040. I was told to do this by the shop that sold me the pushrods and lifters.
Seneca
Elder User
Joined: Jan 2004
Posts: 867
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From: Eastern Pa
I have never heard of that method for checking preload. Try to do it the way that Crane suggests. You should not be turning the engine at all between your measurements. When you do that your changing where the lifter is on the cam.http://www.cranecams.com/?show=techa...638aaad3696991
Junior User
Joined: Nov 2003
Posts: 58
Likes: 0
From: saint petersburg,florida
Fixed backfire problem in my rebuilt 400.
Took everyone's advice. checked wiring, valve train, compression check, went 3 steps leaner on the edelbrock 600 and finally after several frustrating hours that turned into days, I reluctantly took the unwanted advise from a mechanic friend.
He said-" Lose those new Champion spark plugs and put in new Autolite 26 plugs-set @.044.
Well, I did, and that engine instantly went from a backfiring monster to music to my ears. I runs perfect. Thanks to all . Seneca
Took everyone's advice. checked wiring, valve train, compression check, went 3 steps leaner on the edelbrock 600 and finally after several frustrating hours that turned into days, I reluctantly took the unwanted advise from a mechanic friend.
He said-" Lose those new Champion spark plugs and put in new Autolite 26 plugs-set @.044.
Well, I did, and that engine instantly went from a backfiring monster to music to my ears. I runs perfect. Thanks to all . Seneca