I have a 305 that I just put an LT1 cam in. RHS stock replacement heads, headers, rpm intake. Holley 600 dp. Car ran well yet lean before the cam change with 64 pri and 70 sec. Now it is hard to start and backfires severely on acceleration through the carb, sometimes even lighting it on fire. Changed the primaries to 66 and no change. Power valve is a 6.5. I have an air/fuel gauge and it reads rich everywhere with a slow constant throttle, yet drops to dead lean on accel. I am putting a supercharger in it and am waiting on the belts, so I really dont want to mess with the jetting too much since then, but I know that this lean on accel is a bad start. Timing is 12 initial. I have some pump cams on the way. Does anyone have any suggestions to make this a little smoother for me? Would that cam make that big of a difference?

 

How long does it stay lean for on accel? How long are you planning on running before you get your supercharger? 64 was too lean and 66 is too rich, sounds like a tempermental engine, has the weather changed much recently, like in between jet changes? If not see how a 65 works out for ya.

 

ON a Holley carb, 1 jet size is undetectable; 2 jet sizes is the smallest detectable change, usually considered the final tweak adjustment after tuning; 3 sizes is a standard step; 4 sizes is a large step.

In your case I'd try 4 sizes, and a 10.5 PV. That should get the primaries close. Then tune the sec jets for best mph in the 1320. You'll probably end up with about 73s in the sec when you're done.

If this is some POS like a 1850, it's not as tuneable as a better carb, and won't be as crisp on tip-in or get as good gas mileage, because of the inferior cheeepie boosters in it; but you should easily be able to get it not to backfire.

There's no reason to be scared of tuning a Holley, it's ESSENTIAL. Do have a new set of gaskets on hand though, and put a smear of NON-FIBER grease (white lithium or similar) on them when you put it together. Not so much that it gets into any of the air or vacuum passages though.

 

Are you using a standard Holley, or a blower version?

Out of curiosity, where are you in Germany (assuming you're still stationed there like your info says).

 

Its a standard 4776, not sure what specific one though. I changed the floats and milled the choke horn, so I cant play with the choke anymore.....I'm still in Germany, down near Trier. I have to really ease into the throttle for it not to die/backfire and it shoots to dead lean on the gauge. If I ease into it it reads rich at the richest of the spectrum.