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TOPIC: 5.7 in a 2452 - Carb setting - is there an easy way?

5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 14:58 #1

  • TerryW
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Hi,

I did ask this ages ago and there was nothing around at the time but things move on . . .

When tuning a car you can get an exhaust sniffer (o2 meter) to help adjust your mixture. I just wondered if there was anything that will work on a boat with raw water cooling I.e water from the engine block is thrown out with the exhaust. I have a 5.7 sbc with a Edelbrock 1409. I just love that carb. I used it to replace my old Rochester 4bbl. I have "leaned out" the mixture 4% using the next needle down the 1409 range. They provide a chat. This got rid of a lot of the unburnt fuel smell which I personally don't notice but the wife hates. I am pretty sure that the mixture is about right and that I'd need a little bit of tek to improve on the mixture.

Thanks in advance.

Terry

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Terry (Retired Diving Instructor and Part Time IT Consultant)
1998 Bayliner 2452. 5.7l V8 - Edelbrock 1409 4bbl - Alpha1Gen2 - Solent UK.
MMSI 235061726

5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 17:14 #2

  • builderdude
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Good question Terry, if it was me I'd go old school and run it then read the plug color.

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Dave
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5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 19:16 #3

  • CptCrunchie
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builderdude wrote: Good question Terry, if it was me I'd go old school and run it then read the plug color.


Plug color? *blink-blink* As in, spark plugs? I'm just about to replace my Rochester with what the OP has. You mean I could set this carb myself?

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"B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
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5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 19:53 #4

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Yep, spark plug color, the ceramic sourounding the electrode.
Dark to black running to rich, lighter to white to lean. Should look somewhere around the color of cardboard.

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Dave
Edmonds, WA
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'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
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www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 19:56 #5

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Should get ya close.

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556
Last Edit: by builderdude.

5.7 in a 2452 - Carb setting - is there an easy way? 10 Sep 2017 22:34 #6

  • CptCrunchie
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builderdude wrote: Should get ya close.


Wow! Thanks!

Didn't mean to hi-jack the thread, but I'm sure this is info the OP could use.

What does too hot or too cold mean? I thought heat involved the thermostat. But how can it be too cold?

Now, I haven't really looked at the old one, and the new one has yet to arrive. This has 4 barrels, but is there just one set screw to set? And does it set everything; idle and fully open?

I'm guessing the choke will need to be set too, right? It already has an electric choke, so I'll be swapping the wires, but is there anything else I need to know?

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"B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
MMSI: 367637220
HAM: KE7TTR
TDI tech diver
BoD, North Olympic Peninsula Puget Sound Anglers, Sequim, WA
Kevin
Last Edit: by CptCrunchie.

5.7 in a 2452 - Carb setting - is there an easy way? 11 Sep 2017 16:02 #7

  • Centerline2
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CptCrunchie wrote:

builderdude wrote: Should get ya close.


Wow! Thanks!

Didn't mean to hi-jack the thread, but I'm sure this is info the OP could use.

What does too hot or too cold mean? I thought heat involved the thermostat. But how can it be too cold?

Now, I haven't really looked at the old one, and the new one has yet to arrive. This has 4 barrels, but is there just one set screw to set? And does it set everything; idle and fully open?

I'm guessing the choke will need to be set too, right? It already has an electric choke, so I'll be swapping the wires, but is there anything else I need to know?


too hot or too cold, is in reference to the spark plug itself... the plug may be a hot burning plug or a cold burning plug...
if one was to really get into a study of it to dial it in perfectly, you can lean or richen the burn of the air/idle mixture slightly by changing the heat range of the plug... you can change the mixture more by changing the jets or adjusting the rods in the carb...
the thermostat has a lot to do with the heat within the combustion chamber as well, which is why the specific specs for the particular engine and how its set up are so important... but to use as a guideline more than hard numbers that have to be used.

in my opinon, the real advantage of the AFB carb (edlebrock) is that the jets and rods are so much easier to change than in the quadrajet carbs.. but you will still have two air/idle mixture screws to adjust and one screw to set the idle of the engine... and they are much easier to get at than the one in the quadrajet carbs..

the quadrajets are good strong running carbs once you get them dialed in, and if one doesnt tune the AFB to the engine it has the potential to be even worse than what you have now.... but the AFB carbs are good carbs and much simpler. other than the additional cost, the only solid argument that can be made for not replacing the quadrajet with an AFB is that, if you take the time to dial it in, in our sport boats the quadrajet will perform as well as the AFB... (its just that the AFB is easier to make changes to, and so it usually gets dialed in closer than the quadrajet ever does, so they have a reputation of performing better than the quadrajet )

the problem to look for in any carb to see if it needs to be replaced, rather than dialed in, is to check for any fore/aft or up/down play in the throttle shaft... if it has play in it, it leaks air at the shaft and may not allow the carb to be adjusted as it was designed... and make sure it is a MARINE carb, as they are designed to prevent fuel vapors from escaping (if dialed in correctly), whereas an automotive performance carb almost always vents to the atmosphere (engine bay)...
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1989 Bayliner 2556, 5.7 OMC Cobra
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5.7 in a 2452 - Carb setting - is there an easy way? 11 Sep 2017 16:48 #8

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to answer the question that has been asked by the OP,
finding/choosing the correct jets and rod settings on a carb is an involved process and can be a much different process on different brands of carburetors, but the procedure for adjusting the idle circuit on any brand of carb is nearly the same..

the initial setting for the air/idle screws on a quadrajet is about 3 turns out...
on an AFB it is 2-1/4....

then start the engine and let it warm up completely and idling about 600-650rpm..... then turn the screws in or out to get maximum engine rpm.... turn one screw then match the amount with the other screw....
when both screws get adjusted without any more noticeable increase in rpm, turn the rpm back down to where it was before adjusting the mixture screws... and then adjust the mixture screws again the same way....

do this 2 or 3 times, turning the idle down each time afterward.... and there will be a time when turning either mixture screw wont increase the idle any more.... it is now adjusted to its very cleanest burning setting, but it may stumble during a hole shot due to it being lean at idle..
if this happens, then you need to turn the screws to the left an eighth of a turn, to a quarter turn to richen the idle circuit so the transition to WOT can be made without a hiccup..

a digital tach helps a lot with this, and sometimes the screws may be slightly in or out a bit from one another, but more than a quarter turn out of sync means there is an obstruction somewhere in the air idle circuit....

and yes, there are other and more expensive tools to make the job go quicker (easier?), but in the end, for top performance, its the man that makes the adjustments.. the machines just get it close.
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Last Edit: by Centerline2.

5.7 in a 2452 - Carb setting - is there an easy way? 11 Sep 2017 17:38 #9

  • dktool
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TerryW wrote: Hi,

I did ask this ages ago and there was nothing around at the time but things move on . . .

When tuning a car you can get an exhaust sniffer (o2 meter) to help adjust your mixture. I just wondered if there was anything that will work on a boat with raw water cooling I.e water from the engine block is thrown out with the exhaust.Terry


If you have the skill level and access to a mill, there is a very good solution available for AFR tuning in marine applications.
I have installed this ARF gauge in a few vehicles although not in a boat yet, but it is on my back burner list for my boat.
It is a very good unit. It's nice to see someone came out with an adapter for old school marine applications.

howellefi.com/general-motors/gm-tbi-prod...nsor-for-marine-use/

www.amazon.com/gp/product/B01F46VJ4U/ref...06_s00?ie=UTF8&psc=1

This would be the best choice for an in dash mount, same gauge without the cup mounting.

www.amazon.com/AEM-30-0300-Wideband-Sens...7R7WSWHKPNAH58JAP7ST


There is also this if you have the vertical clearance and can work around the exhaust hose alignment issue that may occur.

www.ebay.com/itm/like/161830008582?chn=ps&dispItem=1

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1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
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5.7 in a 2452 - Carb setting - is there an easy way? 12 Sep 2017 06:50 #10

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Centerline2 wrote: the problem to look for in any carb to see if it needs to be replaced, rather than dialed in, is to check for any fore/aft or up/down play in the throttle shaft... if it has play in it, it leaks air at the shaft and may not allow the carb to be adjusted as it was designed... and make sure it is a MARINE carb, as they are designed to prevent fuel vapors from escaping (if dialed in correctly), whereas an automotive performance carb almost always vents to the atmosphere (engine bay)...


As pointed out here , the fuel was leaking a steady stream onto the manifold from the throttle shaft. That's why I need a new carb. Besides that, the butterfly valves are corroded and the smaller ones are rusted. It was time.

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"B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
MMSI: 367637220
HAM: KE7TTR
TDI tech diver
BoD, North Olympic Peninsula Puget Sound Anglers, Sequim, WA
Kevin
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