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Very Strange Phenomena - Need Advise

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Hi all;
I have a strange phenomena happening. We are working on a 302 (bored to a 306) Ford motor. Fast! At idle, you can put your hand on the #7 cylinder and its cold and also at steady rpm it seems to be misfiring as well out of #7. Here are all the things we've tried so far and none of them have remedied the problem:

1. Checked/switched around plugs and wires - no change.
2. Switched with a new distributor - no change.
3. Messed around with different carb settings and jets (its a 670 Holley) - no change.
4. Ran a compression check in the cylinder - no problem.

Now under acceleration, the tube starts to get hot and when you are on it, it runs like a dream. However, it is misfiring under no load. WHY? At this point we are thinking its something with the manifold. Here is the manifold that is being used:

http://cgi.ebay.com/ebaymotors/Typh...tegoryZ36474QQihZ008QQitemZ180086917676QQrdZ1

What else is there to check? Any thoughts??? :confused ;shrug
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Valve adjustment,(Some 302's are adjustable,Depending on year)Weak Valve spring,Bent valve,Cracked head,Vacuum leak at intake runner!!:upthumbs
Hi all;
I have a strange phenomena happening. We are working on a 302 (bored to a 306) Ford motor. Fast! At idle, you can put your hand on the #7 cylinder and its cold and also at steady rpm it seems to be misfiring as well out of #7. Here are all the things we've tried so far and none of them have remedied the problem:

1. Checked/switched around plugs and wires - no change.
2. Switched with a new distributor - no change.
3. Messed around with different carb settings and jets (its a 670 Holley) - no change.
4. Ran a compression check in the cylinder - no problem.

Now under acceleration, the tube starts to get hot and when you are on it, it runs like a dream. However, it is misfiring under no load. WHY? At this point we are thinking its something with the manifold. Here is the manifold that is being used:

http://cgi.ebay.com/ebaymotors/Typh...tegoryZ36474QQihZ008QQitemZ180086917676QQrdZ1

What else is there to check? Any thoughts??? :confused ;shrug
 

chevyaddict

Well-known member
Joined
Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Valve adjustment,(Some 302's are adjustable,Depending on year)Weak Valve spring,Bent valve,Cracked head,Vacuum leak at intake runner!!:upthumbs

Well, the motor only has about 6000 miles on it (or less) and was professionally built. Wouldn't a weak valve spring or bent valve show up in the compression check? We've checked the vacuum - seems to be fine and I doubt its a cracked head... the car runs too good and fast under load.........
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Well, the motor only has about 6000 miles on it (or less) and was professionally built. Wouldn't a weak valve spring or bent valve show up in the compression check? We've checked the vacuum - seems to be fine and I doubt its a cracked head... the car runs too good and fast under load.........
It should!!! It could have a Casting Flaw in the Intake on #7 runner, or the Intake gasket it self at head!! Depending on where the crack in a head might be would determine if it would change compression or not!! :upthumbs
 

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