Post Rebuild Issue

[gjames]

I completed the rebuild, 20 minute break-in, first test drive to 5k and yesterday I ran my first track test consisting of 8-10 laps, Power was good 7500 rpm.

Issue: Popping through exhaust under deceleration. When the engine ran good before it needed a rebuild there was little or no popping.

Engine: 2.7L, 10:5 compression, duel plug, Elgin Race Cams , Weber 46s, Electro-motive ignition. 110 octane fuel.

This morning I pulled the top plugs: #1 + #4 were moist. #2 +#3 light gray. #5+#6 darker than #2/3.

Recommendations?

[Bigtoe32067]

Exhaust leak around the headers?
How bad is the popping?
What are the cam specs?
Tony

[gjames]

The popping is consistent during decel. Not horrible, but different than before.

Specs: 314/3 200 set lift and lap 6.2mm cet@ 5.9

[Trackrash]

Lean idle mixture or air leaks under the manifolds, or throttle shafts.

[stownsen914]

What are the plugs moist with - oil or fuel? To diagnose a possible lean running condition, you probably need to do a hot plug check - shut off under power and coast into the pits. Or in your case maybe shut off immediately after a deceleration event where it's popping. But not on a cool off lap. A cool off lap will change what you see on the plug. A wideband O2 to measure the AFR would be very helpful to diagnose a lean condition if you have access to one.

[faapgar]

What are you running for headers & muffler?Quite a variety of exhaust manifold gaskets available as well.Some are thicker with asbestos sandwiched inbetween where others are just thinner metal to be squished.If you drop the headers and check you will see black marks where the exhaust has escaped.Fred

[gjames]

I fixed the problem by going the Carb Synchonization process. The mixture adjustment screws were the key.

Thanks for all the input.