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Discussion Starter #1
Hi Guys,

I wanted some advice in order to jet my rochester.

Im rebuilding my 65 GTO in France, so when i order parts i prefer not mistake.

My motor is stock 400ci YS except from 0.060inch + piston size.

My carb is a R4-M4MC

The jets are 97.

Primary metering rods 48K
Secondary CH

From what info i sourced something between 70-76 jet size could be a good start.

I know its difficult to guess it, but perhaps someone could put me on the way.... Of jet size or tips on the metering rods size.

I called butler and some parts dealer and couldnt find any info. Even on the website not much info on jet size.

Of course carb is rebuild and everything is in good shape.

Hope someone could giuve some good advice

Super Moderator
5,741 Posts
+1 on the book recommendation. Cliff is the authority on these carburetors. I'd also recommend installing a good quality wideband/UEGO air-fuel meter so that you'll be able to tell exactly how your mixtures are running without having to guess or read plugs. Reading plugs has gotten a lot more difficult to do since the advent of unleaded fuel and the additives in it.

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