302 Running Rough

Evilfox · Dec 9, 2008

Hey guys. I'm honestly out of ideas here. I can't figure out why my 5-8 cylinder plugs are bone white.

1-4 look just fine, maybe a little rich. I get great vacuum readings. Compression test was inline with the other side of the block's cylinders. Maybe even a little higher. Slight popping out the driver side exhaust over 2k RPM.

The car bogs down and has a hard time recovering unless you either pedal the gas or give it more gas. I don't see any smoke out the exhaust. My oil doesn't look contaminated with water.

It runs very much like a blown head gasket but I can't just put my finger on what is wrong with it. Figured I would turn here for advice.

Thanks! =)

More info about my engine:
Crane Cams 13006 Cam. 228 int./228 exh. @ 050 .512" Lift
Edelbrock Performer RPM Air-Gap intake
AFR 165cc Heads.
Crane 1.6 Roller Rockers,
Stock crank/rods. Pistons are .030 over.
Mallory HEI ignition
Holley 600cfm 4 Barrel

Firing order is fine.
1-5-4-2-6-3-7-8

Timing is fine, 12BTDC. I've tried advancing and retarding it slightly to no avail.

My plugs are gapped at .035

2nd Mustang · Dec 9, 2008

Looking down into the carb, is there equal amounts of gas squirting into the intake through the primary bores of the carb when manually opening the throttle?

Evilfox · Dec 9, 2008

2nd Mustang said:
Looking down into the carb, is there equal amounts of gas squirting into the intake through the primary bores of the carb when manually opening the throttle?

Yes.

68dustin · Dec 10, 2008

how are you checking your plugs??? at idle or under acceleration? i would try to bump up the jets in the carburator on the primary side. it kinda sounds like you have a vacum leak with the poping out the exhaust. get some carburator cleaner and spray around the carb, brake booster, and intake. listen for engine changes.... rev up

BornInAFord · Dec 10, 2008

You have something wrong that is affecting only one side. I wouldn't suspect the carburetor/intake first. Since you are running the airgap dual plane, if the carburetor would be at fault, both sides of the engine would be affected. If it was a jetting issue only, alternating cylinders would be affected, not one bank or the other. You have one bank running lean and the other rich, so the first thing I'd check would be for header leaks on the driver's side. That's one of the few things in your setup that would affect all cylinders in that bank. Another thing would be the intake gasket and you can spray carb cleaner at the intake/head junction so see if your intake gasket may be leaking. Also run a leakdown and/or cylinder pressure check and get back to us. It may be a head gasket, but most I've encountered with the symptoms you describe would affect one or two cylinders, not the whole bank.

Evilfox · Dec 10, 2008

Today I went out for a drive around the block to get it warmed up and it started spewing anti-freeze out the side of the suspect head. Plugs look the same and my oil doesn't look like it has water contamination in it still but the gasket is most certainly blown. I had a very bad feeling I detonated the other night on the way home.

Thanks for the help everyone. =)

BornInAFord · Dec 11, 2008

Bummer! Sorry about that. It figures it was just on one side. Are you going to replace both head gaskets or just that side?

Thanks for the update, though. Now I can file away more blown HG symptoms in my memory. Let us know if you get it fixed.

Evilfox · Dec 11, 2008

Probably just going to replace both and go with a slightly thicker gasket.

oz · Dec 12, 2008

Are you sure it's the head gasket and not the intake manifold gasket? Usually a head gasket only effects one or possibly 2 side by side cylinders. Rarely does it effect all 4 on one bank. The intake should have a water passage in it as well so just because it's leaking water doesn't mean it's the head gasket - it could be the intake gasket.
Just make sure the geometry between the intake and the heads is correct. If you put a thicker head gasket on, that will push the intake ports further apart. This could effect the seal to the intake and valley...

D.Hearne · Dec 12, 2008

oz said:
Are you sure it's the head gasket and not the intake manifold gasket? Usually a head gasket only effects one or possibly 2 side by side cylinders. Rarely does it effect all 4 on one bank. The intake should have a water passage in it as well so just because it's leaking water doesn't mean it's the head gasket - it could be the intake gasket.
Just make sure the geometry between the intake and the heads is correct. If you put a thicker head gasket on, that will push the intake ports further apart. This could effect the seal to the intake and valley...

Sounds to me like you've got it pegged. He might get it fixed just by simply tightening the intake bolts.

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