ok, I just put in a brand new zz4 350/355 in my 70 rs, and replaced my old carb w/a edelbrock 650 elect. choke thunder avs. it hesitates/cuts out for a second when I hit it down, but otherwise runs perfect. I have put in a new holley 110gph mechanical fuel pump, with dual feed lines, same problem. checked the fuel filter, was dirty, cleaned it, same problem. do I need to mess with the jets or rods to stop the problem? I just had the timing checked at the dealership, it was slightly retarded, but problem still exists. Thanks.

 

It could be a fuel mixture problem. Try swapping a known good Q jet on there and i bet it cures it. My brother and I had the same problem with both an Edelbrock and a Holley ended up rebuilt Qjets back on and have'nt touched them since. A 550 to 650 cfm Qjet will support 355 HP.

 

Have any other mods been made? Sometimes the weights in the distributor are too stiff and won't allow it to advance fast enough.

 

thanks for the advice.
no other mods have been made yet. the engine comes w/an hei distrib from gm performance parts, and a gm alum. intake. i havent adjusted the accelator pump on the carb yet, edelbrock says that might fix it? may have to locate a qjet somewhere, dont have one, but would like to try not to change out the carb, it is brand new w/endurashine. ($430 bucks) and have spent gobs of money already..........

 

Check the setting on the accelerator pump, try a bigger or smaller stroke & see which way the hesitation goes.

 

thanks, I will do that.

 

I've had that problem with a holley carb and backed out the accelerator pump almost all the way and it helped some but I think it still could be the timing. You might want to check both.

 

Read the book that came with the Carb. It tells you how to adjust it. All carbs need to be tuned to each motor it goes on. The Edelbrock Carb is very easy to tune, most of the time its just a rod or spring change, Get a Calibration kit it will come with different power valve springs, rods, and jets
650 is kinda small for your set up, it will work ok but you will get more power from a 750

Where are you located

 

Not necessarily...i think a 650 will be plenty for 355HP. Much better throttle response too.

 

Not necessarily...i think a 650 will be plenty for 355HP. Much better throttle response too.
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It still needs to be adjusted to the motor, yes it will be close, but needs fine tuning