leaner mixture at cyklinders 3 and 4

[johnbuckley]

Took the plugs out today for routine service- number 3 and especially 4 seem to be getting a leaner mixture than 1 and 2. Any ideas why? stock engine with zenith. Could it be a leak in the manifold?

[farmputzer]

Yes, definitly, either the gasket or cracked/broken manifold.

[Patrick L.]

Yep,, I agree.. The rear intake runner only feeds 3 and 4.. Could be a bad gasket, warped, broken or misaligned manifolds..

[johnbuckley]

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Thanks both of you. Just taken manifold off now. Manifold looks ok . Gasket warped and obviously failed also about a 1/16 inch discrepancy between inlet and exhaust facings on manifold (so hardly surprising)- time to get it machined like everybody recommends!