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454 Carburetor question?

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Siddhi

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Hello all,
It has been a while since I have been on. New job and things! Anyway, I have a 335hp 454 and I have been having problems with her loading up and fouling plugs. I orginally posted on here about how the boat would not pull over 4000 rpms a long time ago. For the most part the boat runs great and I have never had a problem, but the fouling plugs and loading up if I let it idle to long is starting to irritate me. So I started asking the previous owner about it and come to find out he put a new carb on it. An automotive carb! I was wondering if there is much difference from automotive to marine and if this is why she loads up on me? If it is can someone give me a couple of options to replace it with. The motor is all stock for now and I plan to put new cam and lifters in it soon. Maybe do the whole thing at once. Also while I am there if upgrading the intake is a good idea can you give me some options for this as well. Basically, since I have to replace the carb (I am guessing). I would like to upgrade so that is why I turn to the gurus here. Any help would be great.
Thanks,
-B
 
Hi siddhi,
Marine carbs should have some sort of baffels in the bowls to restrict the fuel from draining and splashing around and starving the carb. When I was into off road wheeling we used marine carbs for that reson. They worked a lot better on extreme angles and bouncing around.

It sounds like your problem is at an idle so that carb may not be properly adjusted.
 
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what type of carb is it// and yes there is a difference between auto and marine carbs.. basically the vent tubes are different, and a marine carb will have a tygon line connection, that goes back down to the fuel pump..

If the boat used to run right, and now is loading up, i'd say the carb may have some trash in it.. if its never ran right, the jets may be wrong..

its a good idea to go back with a marine carb, the automotive is a fire and explosion hazzard..

what kind of hp are you looking to get when you upgrade your engine.. with that info i can make some suggestions..
 
SIDDHI

If the boat was mine when adding a sall cam I would run a Edelbrock Performer intake good for off idle to 5500 rpms. For the carb I would run a holley 750 double pumper marine.

Just my opinion

Big Red N.C. :cheers
 
As was said, ditch the automotive carb and get a marine carb. The main reason is for the risk of explosions. The shafts of a marine carb are have seal, which keep any over flow of fuel in the venturiis and down the intake. They are metered differently as well. That keeps the fuel curve correct through out the rpm band.

For the record, there are no extra baffles in the bowls. As long as the bowls have the right amount of fuel in them, sloshing it around will have no ill effects.

Dont bother with just changing the intake manifold. There will be no gain at all. Getting an engine to breathe better requires the entire intake system to be upgraded. The manifold is 1 piece to the puzzle. The rest of the puzzle is cam, heads, valves, springs, exhaust system, flame arrestor...
 
Thanks for the info. I will get the exact model for the carb that is on it tonight. I do know it is a Quadrajet. Because when I first got it I rebuit the carb because the boat had setup for about a 8 months. He did go out and crank it but that was about it. It basically has always run like it has since I bought it. The guy I bought it from told me that he use to get around 60mph out of it before he changed the carb. he never took the boat out again after he changed the carb. So I am pretty sure most of my problems are in the carb. Plus I am not sure if the speed number he gave was just to sell the boat or if he used a gps. That could be indicated by the speedo on the boat.

As for what I am looking to get out of it! I would like to get her to run around 60 -65 mph. I would be very happy with that. currently fully trimed I get 48 -49 mph GPS. I am looking to put a cam, lifters, rockers, Carb (sounds like I need this now) and a friend has a stainless gill exhaust risers and headers he will sell me. Any options to get me to this speed would be great.
 
and a friend has a stainless gill exhaust risers and headers he will sell me. Any options to get me to this speed would be great.[/quote]

Gil risers will not fit any headers. Gil risers only fit Gil manifolds. If you are only running 49 mph, you have a serious issue. You have to go over that entire engine before attempting any upgrades. The best place to start is to perform a leak down test on all cylinders. If they test good, then upgrading the heads and induction will be OK to do. If not, its time for a full rebuild.
 
What should be the limit on the leak down test? I am getting my buddy to bring home a leak down tester. What PSI? and What percentage is acceptable?
Thanks,
-B
 
You want less than 10% leakage. However, that is on the optimistic side. The % really depends on how many hours on the engine. An old engine will never have 10% leakage, a fresh one certainly should. Run the test, post the numbers . You will get enough opinions here.
 
Ok I just finished the leak down test and the results are saddening. Here they are:
cylinder 1) 28%
cylinder 2) 72%
cylinder 3) 38%
cylinder 4) 30%
cylinder 5) 16%
cylinder 6) 56%
cylinder 7) 38%
cylinder 8) 30%

I did listen for where it came out and they all seemed to be losing it through the exhaust. So I am wondering if maybe the heads need to be reworked. I did listen in the oil filler cap and the carb but I did not really hear air coming from there. I don't know if that is a accurate diag by listening for the air. I am a motorcycle mechanic and that is how we tell if it is valves or rings. It tends to give us a pretty good idea. So please correct me if I am wrong.

So with that being the results where do I go from here and what upgrades while I am spending the money would be my best bang for the buck? Thanks for the help!
-B
 
Those numbers are terrible. Did you make sure the piston was at TDC when you filled the cylinder with air? If so, and you heard air pumping out of the exhaust, most probable cause are the exhaust valves. Sounds like its time to pull the heads and freshen them up. How many hours are on the lower end of the enigne? maybe its time for a full rebuild?
 
did you do compression as well? i'm curious to see those numbers. those leak down numbers aren't good.
 
:lol: Pull it out, Pull it out, Please pull it out if the top end is tired the bottom end is to. It cost about 250 dollars for some rings bearings and gaskets if the bottom end is not worn bad you can just refresh it. If you just do the heads it will always be on your mind what that bottom end looked like. Last year I had head problems on my dually and I reworked the heads and two weeks later I spun a rod bearing pulling my boat to the lake. I new I should have pulled the motor out and rebuilt the hole thing. You have time 4 months till warm weather.


Big Red N.C. :lol:
 
I am not real sure the hours on the bottom end. The guy I bought it from did not use it that much and he said right before he got it the person before him had the entire engine replaced. New crate motor. I think that was around 2000-2001. But I am not sure how truthful he is either.

I did make sure the cylinder was on TDC compression. The cylinders with the higher numbers I went back after I did them all and rechecked those cylinders. Still cam back with the same numbers. I am very confident the test was done properly and the numbers I got are accurate. I did not do a compression test but I can do that was well to see what the numbers are if you guys need me to.

So with that being said can you give me some recommendations as to what I should upgrade and what I should just freshen up. Thanks for the help!
-B
 
I would pull the engine, If you have the funds rite now. Take it apart and see how every thing looks. If it needs to be bored and the crank needs to be turned, and the heads need a total overhaul I would explore some other options if I wanted more power. You have to figure out if you want to spend 2000 or 8000 in a engine. 2000 if you do all the work yourself that figure is letting the machine shop bore it and turn the crank and resize the rods with average head work. Or for 8000.00 you can buy a GM 502 with 502hp and 567 foot pounds of torque.

Big Red N.C.
 
Dont bother with a compression test. The leak down test is much more accurate. A compression test may still show decent #'s, while the internal leakage was shown to be terrible.
Since you asked for opinions, heres mine.... You have real bad leakage, possibly through your valves, possibly and most probably elsewhere as well. You dont know how many hours are on the engine. You dont know the condition of the lower end or even whats in it. You wanted to make more power but are not sure of how much power you had. You have not mentioned a budget. You have not mentioned what drive you have , tabs, hydraulic steering, fuel system, exhaust, etc etc... That is a short list of what I would need to know before making any recommendations of adding power. Thats if you want it to work safely and efficiently. One good way to go is to search for a complete Mercruiser take out called a bobtail. That will make more power than your present engine and be safe and reliable as well.
I would not simply through a set of heads on that block, at minimum, a full rebuild is in order. I see a can of worms opening there. No rebuild is cheap to do properly. You most likely will have to bore the block, that means new pistons. You may have cast internals, so you can throw all that stuff away. The block may be a 2 bolt main. You can use it, but would you want to? Depends on how much power you want to make.

So, I say state your intentions. Figure out how much power you want. How much power you boat can safely handle, ie: rigging? Your budget? Then we can make a few recommendations.
 
If they put a crate engine in it, that is most likely a car engine and will not have the forged internals neccesary for good power in a boat.
Immagine driving your car up a boat ramp type grade all day and you get some idea of the stress a marine engine has to put up with
 
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