Am I over carbed??
 

I bought a boat with a rebuilt fresh engine it was supposed to be around 600hp and i dont think it is even close to that. My buddy has an 25' eliminator cat with a 330 hp bbc and he spins a bravo 1 24p at 4200rpm's and i spin the same prop at 5000rpm's in a 26' firehawk cat. I was told it was a 800 cfm holley double pumper dont know that for sure the airhorn has been machined off. The only number is P-32. Boat runs good fires as soon as you hit the key, but when it is in gear at idle about 800rpm's it loads up real bad and you can smell fuel big time. Im wondering if the carb is to big the carb needs rebuilt anyway but might bite the bullet for a new one but dont know what cfm. Any help would be great

well ther's more to it than that. there are a whole barrel of things that will define carb size other than displacement. intake velocity is the key to making the carb work right and thats a function of compression ratio and cam shaft and intake manifold and so on. in my opinion you need to know pretty specifically what the mechanical specs of the motor are before you head off to decision making land. your symptom could be a 100 different things. some very very simple and others as complex as the wrong cam/intake/cr combo.

you need more data.

thats is what im afaid of I'll see if i can find the paper work on the engine

Paper work might be a little vague but here goes
454 bored and honed with torque plate .060-.100
chamfer bottom of clinders
balance assembly
install bronze guides
surface cylinder heads
competion valve job
cut heads for valve stem guides
Crankshaft Eagle cast
connecting rods Eagle H Beam
pistons SRP
rings Sealed power
Camshaft Crane 296-2
lifters Crower6600x3
push rods Jesel/comp
intake valves Ferrera F2114P
exhaust valves Ferrera F2120P
Dart intake and i believe it is 9 to 1 compression runs fine on pump gas
hope this helps a bit
thanks in advance

If you are only spinning a 24 Bravo prop to 5000rpms in a 26' cat then you are no where near 600hp. More like 400hp assuming 1.5 gears in the drive.

I could spin a 26" Bravo to 5300rpms in my straight bottom, 5500#, 28' Pantera with 550hp.

As far as overcarbed, an 800cfm Holley is fine for a 500hp engine. Its a little big for a 400hp engine, but workable.

That is what i thought griff, I was guessing 400-450hp. Do you think a 650-750 cfm would be good

You are NOT over carbed...you just need to have the carb jetted and float bowl levels adjusted....find a knowledgeable mechanic or someone that drag races and have them dial it in for you.

Fixx
 

yake the 2 screws on the side of the metering block and turn them in all the way but count the turns,,if theirs more them 1 turn max then they are out to far..try 3/4 turn out and see how it idles. with holley carbs they like heat,if your rngine is not building enough water temp's then it willl load up..,ake sure the engine temp is up to 140* before massing with the carb..
back to the carb,those small screws are the idle rich or lein screws.turning them out will fatten the idle mixture,turning in will lein the idle out. turn them a tiny bit at a time and let the engine clear its self..
If you have the wrong power valves in the carb that will also make it run rich but thats a whole another wat of tuning a carb..

the info on that paperwork is not what you want. you want the cam specs, installed position and true mechanical cr. but, never the less... you can certainly start twiddling screws and metering blocks and power valves but in my mind you are jumping to conclusions based on no information at all. you have two symptoms... 1) emprically you believe you are way down on power based on observation 2) you have what seems to be an excessive rich condition at idle.

your conclusion is " bad carb" . now... if you had a year or two experience w/ the boat and knew its in's and outs , and knew that last week it ran perfect and had high top speeds etc, them maybe that sort of " conclusion " would be warrented. it would be the most logical deduction. but the fact is that you don't know anything about anything. the timing could be wrong by 30 degrees. the firing order could be wrong, the thing could have 40 pounds of compression in 3 cylinders...

you have to have a reasonable knowledge baseline to start with. do the simple stuff first. track down the engine builder and get the cam , piston and head specs. shoot the timing, confirm the firing order, do a compression and leak down, have the the plugs out and look at them... make sure the ignition is strong and advances properly. if it has an msd of any sort, throw it away... etc etc. make sure all the easy stuff is correct and that you know where you stand on all the rest... THEN at least you have a place to start. and certainly, the easiest thing to do ( and why carb guys love carbs and not efi) BORROW a known good carb from your buddy w/ a similar set up and see if its any better...will take you 15 mins to switch it.

also... if it really is wildly rich, you would be well advised to find that reason before you put a lot of time on it. running a motor rich like that wears the hell out of it quite quickly.

Good advice. :drink:

ck timing at full advance and initial....pop off primary float bowl and mettering block, see if back side of power valve is wet with fuel...blown power valve and not enough initial timing can make it run rich at idle..start there

Thanks for all the info, glad this site is around as i'm not as good with engines as i would like to be, but learn new info off this site on a daily basis Thank you all and Happy Fathers Day to all the fathers out there

A 750-800cfm is the correct carb. I ran an 800cfm carb on a 420hp/454. Its on the large side, but nothing extreme and plenty useable.

well thats the ultimate conundrum, isn't it ? do you want to go boating or do you just like the technical challenge or something in the middle or combination ? none of this is rocket science but not much of it is intuitive or self evident either. . you can shotgun solutions, guess at things , twist wires and and tape things and believe all sorts of voodoo and folklore and waste lots and lots of time and money trying to do things that you simply don't have the knowledge or rxperience to do... or tiy can just find someone that actually knows what they are doing to do the work and train you as necessary to do it yourself in the future. ir all depends on what you ultimately want to accomplish and how you want to spend your money. you can spend it trying to do things you don't know how to do and hope you get lucky and don't screw something up and spend a lot MORE money fixing that... or you can just get the thing sorted professionally the first time and make sure you get the knowledge and training necessary to do it yourself in the future . an example ... before that boat even ended up in your driveway , had you ordered the factory workshop manual for the motor and drive ? i know this all sounds like philosphy rather than how to fix your hardware but without the right mindset going in you may as well just take your money and pile in the backyard and light it on fire and save yourself the time towing the boat to the ramp.

The symptoms of being "over carbed" is no change in performance between 3/4 open throttle and full throttle. It sounds more like you have jetting problems or a stuck power valve. If you have a large cam with a lot of overlap, low RPM response is going to be bad. Part of this is because there is little vacuum at idle in the manifold with a large cam. Carbs, unlike electronic fuel injection have "circuits". There is an idle circuit, an intermediate circuit and a main circuit. The fuel and air have to transition between these circuits as it is being metered. Carbs work using pressure differentials through venturis. If the air flow is moving back and forth in the manifold or intake runner while the engine is loping along at low rpm's, the carb has a hard time metering the air and fuel in proper proportions. Hence..... the "loading up".