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Am I over carbed??

Old 06-18-2011, 03:56 PM
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Default 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
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Old 06-18-2011, 04:40 PM
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Originally Posted by firehawkcat View Post
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.
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Old 06-18-2011, 04:46 PM
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thats is what im afaid of I'll see if i can find the paper work on the engine
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Old 06-18-2011, 05:06 PM
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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
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Old 06-18-2011, 06:41 PM
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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.
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Old 06-18-2011, 06:53 PM
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That is what i thought griff, I was guessing 400-450hp. Do you think a 650-750 cfm would be good
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Old 06-18-2011, 07:13 PM
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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.
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Old 06-19-2011, 12:26 AM
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Originally Posted by searaycer View Post
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.
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..
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Old 06-19-2011, 04:39 AM
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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.

Last edited by stevesxm; 06-19-2011 at 04:45 AM. Reason: sp
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Old 06-19-2011, 07:28 AM
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Originally Posted by stevesxm View Post
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.
Good advice.
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