I'm running a holley 4bbl on a 383 stroker and it's stumbling a bit at 600 r's... tried bumping up the idle a bit and it runs/sounds much better at 800 r's but, then it diesels when shutting her down. Any suggestions on how I can troubleshoot/fix this? I'm definitely a novice when it comes to tuning carbs...

Here's a pic of the carb to help ID the carb as I'm not sure exactly which size it is.

 

A couple things you can do:
1. Remove the plug from the air inlet tube, the brass plug just above the fuel line. This air passage is inlet air for the choke pull off behind the black cap. Holley has a filter for it.
2. You have ported vacuum going into the hard line and to the rear of the eng compartment. You should blank/cap off this nipple and tee into the full manifold vacuum, the same line going to the dist.
3. You can open the secondary plates by screwing in, or screwing, the stop screw in the base plate under the sec diaphram. Best to remove the carb, screw the stop screw through the base, then turn the setscrew over and thread it from the top for better adjustment.
4. Use a vacuum gauge to tune the idle circuit, idle mixture screws, initial timing, and adjust for best vacuum reading, highest indication on the gauge.

The idea is to close the primary throttle plates further preventing dieseling.
If the camshaft is other than stock, you will need a little bypass air, meaning open the secondaries alittle, then you can lower the priimaries.
Also, you can adjust inital timing for best vacuum, but, you don't want too much as to kick back against the starter when engine has sat and heat soaked.
Using full manifold vacuum on the distributor is a trial & error call. Try it both ways and compare the results of each method.

 

Aftermarket distributors are designed to work on "smog era" engines, which means advance hooked up to ported vacuum. Unless your vacuum advance on the distributor has been "tuned" to work on full manifold (different vac can, w/a travel limiter on the plate), your engine won't run right. The way you have vacuum connected, you're pulling full advance at idle. I'm figuring that other vacuum hose is going to the modulator on the trans. Swap where the vacuum hoses are connected at the carb, and while the hoses are off, check the ignition timing. Your initial timing is likely set way retarded to compensate for the manifold vacuum pulling advance at idle.
Leave that brass cap and plug on the choke housing the way it is. That's for sucking in warm radiant air from the intake manifold to operate a choke pull off. But, your choke is electric instead, and doesn't have the warm air setup, which is why the plug is there. Without the plug, you have an open vacuum leak.

 

...WHAT WAS the outcome on your problem ...
Thanks

 

I put a new 750 Holley on this spring and now it starts right up every time and no more dieseling,,,,