delsol

Does anyone know of a thread on tuning 4500's, or a link to where I can find it on the web?? I've tried a searching but can't seem to find anything relevant. I need to set up my idle circuit amongst other things -- running too rich and fouling plugs. Thanks

Airpacker

One tried and tru method of controlling over fuelling at idle on a 4500 if your main jetting and power valves are correct for midrange and WOT is to drill 4 small vacum relief holes in the throtthe plates very close to the fuel discharge ports in the carb. This reduces the vacum applied to the idle circuit and reduces the amount of fuel drawn into the engine at idle and just off idle. Start at 1/16 inch and move upward as needed.

delsol

Airpacker -- thanks for the reply -- I've heard of this, holding off until i run out of other things before i start drilling. There are no power valves in these carbs -- blocked off-- after talking to a few people they had told me that on a boat i had to have them so i don't load up because of too big of jetting in the idle circuit. On the dyno one carb ended up with 97's on all 4 corners, the other with 100's all 4. On saturday we dropped down to 94's primary and 95's secondary, was better but still way too much fuel especially at 3200 rpm. These have 3 air bleed circuits in them-- is it possible to tune with just the airbleeds or should i just throw in some 5.5 or 6 power valves and drop the jets by 10 and start again??

Airpacker

I always use power valves in 4500's in the primary side. u really need to know what vacum you have to work with before desciding on a valve though.

PatriYacht

I'd drop about 4 jet sizes and put in 4.5 power valves to start. Don't want the power valve to open too early or you'll be over fueling at 3200 again. Standard Holley jetting in these carbs is 88's. Can't see going lower than that.

delsol

After further inspection i realize that the metering blocks are not blocked but not drilled and tapped at all. I tryed a set of 1150's with power valves (6's) and 89 pri and 92 sec. last night -- they idle and ran much better. Unfortunately I didn't get a chance to set the float level before a huge rain came in. As i was trialing them, after a couple of minutes at 4500rpm the 1 motor died flat -- i think it just ran out of fuel in the float as it started right back up. I have to pull the plugs --as soon as it stops raining around here.
I got a price on new metering blocks --$145 each US -- Could I get away with just puting the power valves in the primary side?? or do I need 4 of them?? At that price I'm thinking about buying new carbs and possibly dropping down to 1050's , as when i did the formula for CFM it came out to 1029 cfm. Any ideas???

BenPerfected

Del,
I have great success with the Holley 1150 CFM #7320 2-circuit dominator on 500-509 Ci engines. I just did dyno testing vs. nunerous tricked out Dominators. The box stock #7320 (available at Jegs) made the most power. This carb comes with two power valves. It idles great and when you get the power valve right, it will leave the transom soot free. On my combination I run a 3.5 PV. I would start with a 5.5 PV and and run around at 3000-3500RPM and then reduce the PV size until the soot disappears. Based on your dyno test, you might consider starting with 97's in the secondaries w/o a PV, and then and 89's with a 5.5 PV in the primarys.

mopower

I have 540's with 92's around and no p/vs... I'm sooty. And have even fouled plugs. Going to try 88's this weekend

delsol

Thanks for the reply Benperfected-- Wouldn't you be able to better fine tune a 3 circuit tho? Or just rely on the power valves to fine tune the 2 circuit and keep it simple??
If this is the case, then it looks like i'm going to have to buy another 2 new carbs! Would the 1050 work better or for marine should you have that much more air in the 1150?

BenPerfected

Del,
Getting the three circuits to work is not easy. The #7320 1150 out of the box is a no brainier. There is an old Powerboat Magazine Teague article also that says the 2-circuit is the way to go. The 1150's made 25HP more on my engines than an a Barry Grant modified 1050's in a 1998 dyno test. The same 7320's beat a Sterling modified 3-circuit 1150 #80556 by 3-5HP in a 01/04 dyno resting.You could probably sell your 1050's for $300 ea and buy the 7320's for $739 ea...headaches over.