Carb Suggestions for 5.7 Hemi

[Map63Vette]

So I've had my 5.7 swap project done for a few weeks now and back on the road but am still trying to tie up some issues. I got an Indy Mod Man intake (single plane design) for the hemi so I could do a carb setup and am running my old Carter Comp AFB that was on the 318 that was in the car. From what I can tell, the carb is a 625 cfm model with weighted secondaries. The timing is taken care of through an MSD 6 Hemi ignition box (basically an electronic distributor that I can set a vacuum and mechanical curve in). It comes with a canned tuned that is designed for stock engines, which mine is aside from headers and the intake and carb setup.

The car currently has some stumbling issues off of low rpm launch like a stop sign when I drag the engine down a little too much clutching it and has hesitation under hard throttle. I'm not sure if the low rpm is as big a deal because I don't have my tach working yet and I might just really be dragging it down, but the hard throttle hits are annoying. It seems like the problem happens probably right when the mechanical secondary blades are starting to open, but since they are weighted they aren't exactly easy for me to modify to test. If I keep the pedal under half throttle on a hard hit the engine takes off fine, but any more and it starts to stumble and bog before coming back up.

Anyone have any suggestions as to what I might be able to do to fix the problem? I rebuilt the carb and have tried all the accelerator pump settings, but it didn't seem to make much difference. I looked into picking up a different carb at a swap meet, but didn't really know what to look for or if it would even fix the problem. I had heard that on full throttle when all the blades are open that the fuel may not atomize well initially because of the drop in vacuum, but would a different carb fix this?

 

[Johnny Mac]

you spent all that time and money on what sounds like a very badass new hemi build...not sure why you are skimping on the carb..the last thing i'd do is reuse an old carter 625 that was setup for my 318...i think you know the answer to your question before you asked it...a new holley 750 DP sounds alot better to me.

 

[furz4]

I think you could make the carter work but you would be better off with a larger carb. It is most likely too lean if it was set up for a dual plane on a 318 to begin with. I would put a vac gauge on it to assure no vacume leaks. If it was me I would get at least a 750 on it. If your running highway gearing 3.23 or above I would probably use a vac secondary carb. The intake your using has a much larger volume then the one you had on the 318 so it's not surprising you are having some issues.

 

[johnparts]

750 Holley Vacuum secondary 3310

 

[Map63Vette]

It was actually a pretty cheap build to be honest. I was really just trying to get the car back on the road with stock parts to start with and then look into ported heads and performance goodies later. I only reused the carb because I had it and figured it would work for now. The trans is 73 833 (non OD) and I've got a set of 3.55's in the rear axle. I really don't know the first thing about carb selection and tuning aside from how to rebuild them. The car seems to run fine on the low end, doesn't smell too rich and the plugs looked pretty good, so I wanted to make sure the carb was the issues before throwing a lot of money at one. Didn't really think about the plenum volume being so different, that makes some sense. The car is really going to see the street most of its life with an occasional trip to the track maybe once or twice a month if that makes a difference.