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Need some carb help! Running a holly 850 dp on a fresh 496 chevy bb and it has power valves. Am noticing the fresh oil is getting dark. (New motor with 4hrs, static compression is about 180psi). Im thinking the power valves (4.5)are hanging open and loading more fuel then necessary. Am I thinking wrong? I know the pv should stop flowing after a higher vacuum is reached but with the cam I have (571/556-224/234 @50 with a 114 I have about 9 inch lbs running it in the driveway. Im going to run it tomorrow with a vac gauge to see whats what. The pluge are bit on the lean side, running 80's 4 corners so that makes me think it cant be the pv's dumping fuel????????

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Pulled the pv's out and blocked them. Went to 86f 87r and upped the squirts to 45. Throttle response is better. Going to run it tomorrow and see what happens.

FIXX

iTrader: (2)

if the oil is getting dark its not the carb doing it,its most likely the engines oil is getting hot and thats why its changing color..you will need a bigger oil cooler and a oil temperature gauge to determine how hot the oil is getting..when you block off the
pv's your soppose to go up 10 jet sizes..4.5 power valve sounds rite for your vacume range..also check it at 2k and see where its at..

Griff

IMO, you should run a PV in the primaries. Increasing the jet size is just like having the PV open all the time anyway.
A 4.5 PV opens and supplies more fuel when vacuum drops below 4.5 inches.

Have you tuned the air bleeds to attain max vacuum at idle??? What is base and total timing set at???

I also doubt that the dark oil is being caused by the carb.

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Thanks for the info guys. I was wondering about the oil cooler. I picked up a set of 3.5pv yesterday so I'll chk vac in gear today to see whats happening. I never thought of running just one pv on the primary side. The base idle is at 10. Seems to run best there, I had it at 8. Ill check total today.

PatriYacht

180 psi is fairly high for a marine engine. Combined with a lean condition, that could easily lead to detonation and engine failure.I agree with mrfixall, your oil is getting dark from excess heat. Do you have an oil temp gauge? If not, get one. All perf. built engines should have one. Put the sender in the oil pan. Never let the temp go over 280. If you're darkening the oil quickly now you are at 260 already and good posibility much more. Good luck.

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Picked up a gauge and will install soon. Total timing is at 33. going to go back to p/v tomorrow. When in gear its at 7 to 9 inch lbs so I going to go with 3.5 and 80 on all 4 and see how things look. Dose anyone know the factory setting on a Merc 525 carb? Is anyone running a 496 with a 850? whats your carb set up. Thanks.................

Skatermac

Carb is too big. If the oil smells of gasoline change it before you kill the rings. Barrow a 780 or 750 vacuum secondary and see how you like it.

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Have a set of 502 rect port heads, Performer Air gap, 9:25 flat forged pistons, Scat forged steel crank, Scat 638 rods, Crane 553/571-236/246 with a 114, duration 296/306. Ran the boat full throttle yesterday and would not go over 4600. This is the same as my old 496 peanut head, stock intake, 510 lift cam motor! AAAAAAAAAAAAAHHHHHHHHHHHHHHH. So, going to jet it down to 82/80 with a 3.5 pv. Im thinking this set up would have pulled 5500 all day long with a 14 1/4 24 four blade... ugh....

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I am using the same prop from previous set up