I have a holley 750 with vacumm secondaries on a zz430 motor. The primary's are 73 jets and the secondaries 71's. It has a hiccup when you drop your foot. Then it will miss when your pulling hard. What should I do first?

 

1st, give us the part number of your carb. There is more than one type of 750 vacuum secondary Holley out there. Is this carb new or used?

Next, "typically" the secondary jets are larger than the primaries (but not necessarily). It sounds like you have two problems: 1) The secondary mixture is too lean, and 2) the secondaries are opening before the engine can use the extra flow. Both are tuning issues. I'd suggest richening the secondary jets until the missing under heavy load goes away, then tune out the bog with progressively heavier secondary springs.

This assumes that your ignition is in good shape and you have the timing set correctly. If you're not sure about those things, get the ignition up to snuff before trying to tune the carb.

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Thanks five7kid

The Holley is a 0-80508s with a secondary metering block. I bought it new with the zz430 it only has about 500 miles of use. The Hei also came with the motor and was recurved for the engine by salle-chevrolet. Im pretty sure the the HEi is Ok. Salle chevrolet also put the lightest spring in the Carb the the secondaries would come open sooner. Thanks for the info Ill see what happens with the richer jets and stiffer spring

 

I told you backwards 71 in primary 73 in the secondary. Could I still be to lean on the secondary side?

 

check your float levels also.

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