How do I tell if I am running too lean?

[Jeeptruck]

Recently rebuilt my carter BBD and worried that I might be running too lean. How do I tell? Right now the mixture screws are out about 2.25 to 2.5 turns. Maybe just nervous because my J10 never ran this smooth....

[ March 24, 2003, 06:39 AM: Message edited by: Jeeptruck ]

[JeepFreak]

If you are running too lean you will know it in a hurry. I just finished with a 360 with a 2150 carb that was running way lean. Anytime I would give it part throttle it would start pinging. If I gave it full throttle it would go away. I just drilled the jets and the problem is solved.

[Stuka]

Another way to check is to pull some plugs. If they are al white you are running lean. Tan = just right, back = rich/oily.

Also the engine will run hot.

[Serious Johnson]

JT:

Good advice above. Some further details:

To check plug color, run the thing on the road for a good while in the speed range of most interest. Arrange to shut the motor off immediately, with no signicant idle time.

Also, lean detonation can partially melt the electrodes, and often results in little baked-on spots on the ceramic around the center electrode. Really bad detonation can crack that insulator, but by then the pistons likely ain't real happy either.

And, bear in mind that the idle mixture screws affect only the idle. Above maybe 1,500 RPM, you could take them out and plug the holes with mud to no effect on the mixture.

One last thing:
Lean cruise mixture can cause an annoying "surge" at constant throttle, and a sag in power on throttle tip-in. Problem is, other stuff can give the same symptoms.

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