Carb tuning
 

Ok boys I have a 477 BBC with cast iron rectangle port hi-performance gm heads. Pretty mild motor 4" stroke, 6.135 rods with flat top forged pistons. The compression ratio comes up to about 8.25:1 on the engine. The cam is a crane 168731. So it has a b&m 250 blower and super chiller intercooler on top running about 8psi boost. The issue I haveis the idling of the boat and when shifting into gear, the engine is constantly surging at idle and in gear. This is a Dean Nickerson carb but it wasn't originally set up for my engine. So if I wanna fix these issues myself what's the best route to go? Carb is set up with 96 jets all the way around and has 3.5PV in front and rear. Carb is also nor boost referenced.

Also this is a 1050 dominator carb.

fixx
 

you can correct a little bit by turning the air fuel mixture screws on all 4 corners..it could be lein or it could be rich,depends on what the exhaust smells like..it its burning your eyes at idle then turn all of them in equal but only a tiny bit at a tine until the idle stabilizes.it also depends on what internal has been done to the carb but try this first..

+1 also an engine balancer would help, start cutting cylinders out should give you a very good idea which corners are richer/leaner. With four corner idle you can really dial in the idle of a carb. Another thing to think about is a locked out distributor, cleaner idling is a huge advantage to that setup; the more advance you run at idle the smoother it will run

Dist is locked out at 30deg. I've worked on the idle screws every way possible with no luck on the idle surge. If you set the idle at a 1000rpm or higher it's smooth but going below 1000rpm it's surging constantly.

fixx
 

start out with a 1/2 turn on all 4 screws no more then 3/4 turn..if your too high on the idle screws then you will bypass the air fuel mixture circuit in the carb and turning the screws wont do anything..also dont expect the carberator to react rite away,it may take up to a minute for the cylinders to clear..give all 4 a tiny turn and walk around your front yard lol...

What is the position of the throttle blades to the transfer slot? What is the proportion of the front to rear throttle blade opening?

I've tried settin them with up to .020 of the slot showing past the blade to the blades being fully shut. I can even back the idle screws all the way off. I'm thinking the idle circuit is just way off for my motor.

Plus I'm figuring it's been altered a good bit by Nickerson performance since it was built for a blower and isn't boost referenced.

30 deg total timing is not enough,espically with the low compression ratio,merc ran 35 deg with the sc 525,i recomend 34 or 35 deg with your setup,it will also clean up your idle somewhat.