I am planning to change my lifters, springs and rocker arms this winter. Its on 2000 model year carb HP500s with 170 hours. Who has the best price on replacement parts and what tool should I use to compress the springs? I do not plan on removing the heads. JEGS has a few different tools but I don't know which one is better or easier to use.

Thanks

Shawn

Keeping it relatively simple, the problem with overcarburation is that is an engine can't pull the volume of air through it necessary to pull equal amounts or air and fuel, you are going to have raw fuel entering the engine...problem being that gas in it's liquid state does not burn. If fuel went directly to the venturi from the float bowl,it would discharge as large droplets. Since a good air / fuel mixture is important to efficient combustion,large droplets would be a poor way to start things off. The air bleeds allow air to enter the circuits. Through emulsion tubes, the air is mixed with the fuel. So an air / fuel emulsion is what is discharged in the engine, not just fuel. Another function of an air bleed is to prevent a siphoning effect form draining the float bowl into the engine when it is shut off.

Ultimately, what screw's up how a particular carb functions on any given motor, is the ability or capability of the engine to pass air through it with no restriction, and the Emulsion Tubes that mix the fuel and air. The fuel that is discharged from a carburetor is premixed with some air to make an air fuel emulsion. This is done in the emulsion tubes and the air comes from the sir bleeds. The air bleeds connect to the emulsion tubes in the well. The tubes extend down into the fuel well and have small holes to allow air to get pushed in to the fuel as the fuel travels up fuel the well. The amount, size and location of the holes in the emulsion tubes all have an effect of how the air mixes with the fuel.

If you have a carb that can flow 500 CFM in the same application and still properly atomize the fuel, it should make more power than a 400 CFM carb. From this perspective, larger is better. Ideally,a carb would present zero restriction to the intake stroke. Such a carb would have an infinite flow rating. Unfortunately, carbs require a pressure differential to properly mix fuel with air, which is why carb sizing is important. Keep increasing the size of a carb and, at some point, the booster venturis will not properly atomize the fuel/air mixture and droplets of liquid fuel will be pulled into the cylinders. Not only is this bad for performance, it's also hard on the engine. The liquid fuel tends to wash oil off the cylinder walls, increasing ring and bore wear. This is a particular problem with engines using large
overlap cams, since they provide lower vacuum levels. When using a larger carb and cam, proper tuning (carb and ignition) becomes more important.

It's important to understand that the basic sizing formula is just a guideline. It ignores a number of important factors such as manifold design, cam timing, weight,intended usage, load, etc.
Furthermore, it ignores important differences in carb design like venturi efficiency, bore layout, and secondary style and method of actuation. In practice, I have found that the basic formula for carb sizing applies mainly to square bore carbs with non-air valve secondaries (Holleys), and even then it can be conservative for a performance application. It typically yields a compromise of fuel efficiency and power.

Using a dual plane, divided plenum, intake usually allows the use of a carb with a larger CFM rating than with a single plane, open plenum, intake. This is because the divider cuts the effective plenum volume in half, increasing the signal to the boosters. Because of this fact, Edelbrock suggests multiplying the CFM predicted by the basic sizing formula by 1.1 to 1.3 for single plane manifolds and by 1.2 to 1.5 for dual planes.

Also, once you have a carb installed, you can determine how restrictive it is by using a vacuum gauge to measure the difference between atmospheric pressure and the pressure under the carb. With the air cleaner removed, the air above the carb will be essentially atmospheric. If there's any difference between it and the pressure sensed under the carb, it's due to the carb. The higher the difference, the greater the restriction. Measurements should be made at wide open throttle and 0.7 inches of mercury is considered non-restrictive.

This may be a bit confusing, but the jist of my point is, if you bolt a 1100 CFM carb on a motor that is designed to run a 850 CFM to match the mechanics of your motor, such as camshaft selection, intake configuration, exhaust flow and design, volumetric efficiency, max RPM, load, and venturi design, you are going to be passing raw fuel through the motor at some point, killing the power curve, and rinsing down the cyl walls, which not only removes the protective oil film from the cylinder walls promoting premature wear and failure, but you are also diluting the oil with gas, and in turn ruining the bearings and any other chance of longevity your motor needs to live past a couple hundred hours under the demands an Offshore boat operates under (or we put them under) .... and that's a fact!

when doing the math you have to factor in volumetric efficiency.

it's hard to cheat physics! the low pressure created by the downward stroke of the piston and it's volume is X.....at 100% VE it can only be X!...now you can actually bring in more only when inertia is still ramming home the IC when the piston is moving upward....thus VE is>100%....and you can never do this when over carbed!...plus fuel atomization goes to ****..

FindMe:
Nice oratory on carb theory! Pretty deep, but good stuff. And I stand corrected somewhat. The atomization is the key here. If you can get good signal from the boost venturies it could work but makes setup a much more critical with a large carb.

Joe:
Yup, gotcha man. Still, see below.

The thing I wonder about is whether these new dominators have annular boost venturies which are supposed to help increase the signal. I know folks have used these carbs quite successfully but I believe the power level was closer to 600 hp rather than the HP's 470. Like you said, X is X and VE=100% and no more (if all works well), but at the higher volume that can be fed by this size venturi to a 600 hp motor, they work.

Also got into Dennis Moore's Big Block Marine book and checked his info. Carbs over 850 cfm are not recommended on engines under 550 hp.

When we were running it was quite rich but there was no bog and actually the seat-o-the-pants dyno indicated more punch even down at 2000 rpm. However, top end was rather flat. Hmmm, just opposite of what you would expect. Well we'll find out in a couple of weeks when the motors are back up and then the guy working on them gets the fun job of dialing in these beasts. The heads are to get some massaging while they're down for freshening. I still question the returns he'll get without changing cams to get more into the cylinders.

Appreciate the comments. Education never stops. Made me get the books out again.

Thanks, Scott