I am running a 468 BBC with 67 L34 heads (oval port, closed chamber), a mild .533 lift .228 duration crane cam (Hydraulic, flat tappet). The carb is a holley 750 DP.

I was running too rich so I leaned the carb out and went from size 72 jets to size 68 jets. I now have a slight hesitation on acceleration. When running the size 72 jets there was no hesitaiton whatsoever. I am running the timing at 16 degrees BTDC.

I also changed from AC Delco 44 to 43 spark plugs. I still think I am running a little rich because the plugs are black and I can see slight black coming from the exhaust when I acclerate the engine in neutral. Otherwise it runs great.

Any ideas on the next step to gettting the tuning correct?
Thanks
Tom

i'd only change one thing at a time, you figure it out. could the power valve be stuck? maybe with leaning it out,now you need to adjust the accererator pump to come in a little sooner?

68 is lean,go back to the 72's and check your powervalve.
You might need a bigger squirter too

Tom, the DP's are a little rich by design. I don't think you will ever get a musclecar especially one with a cam to smell as good as a cat-equipped car. Is it rich at idle, or elsewhere? Jetting has no effect on idle richness. I went down to 68's once and my car stumbled also.

Best thing to do is (for a somewhat cleaner idle) is to make sure you transfer slot setting is correct). Also, try and run the mixure screws in as far as you can - this makes a big difference on the overall richness.

As stated above 72's in the primaries are about right for your motor,68's are too lean.

The rich idle is likely the bad or incorrect power valve for cam idle/low speed vacuum.

Check idle vacuum which should be around 10-12 inches with that cam and is so get a 5.5 or 6.0 power valve to be on the leaner side or 6.5-7.0 to be on the richer side of the power circut when the motor is under a load like when a WOT.

I also ran the Crane 228 deg int dur @.05 cam in a 396 and that cam likes a little more intial timing like 18-20 deg so bump up the initial timing to at least 18 deg btdc before checking your idle vacuum.

Lastly going to a colder heat range plug like the 43's will not help you when your running rich in a street motor. With your motor dialed in correctly (initial timing to 18 deg,jetting to 72 prim,powervalve to 6.0) i would think your motor would like the 45's (plugs) best but if they are too hot which i dont think they will be then go back to 44's.

Have fun dialing your motor in and let us know how you make out.

Scott

Thanks for the response guys. I am going to change the setup this weekend. I will let you know how it turns out.
Thanks
Tom

Thanks for the help all. Here is the final. The Holley is jetted at 70. Timing at 18 TDC. Plugs are R44. The combo works great. The engine is very reactive with no hesitation and has great low and top end.