Tune up for 5.7L Carburated Mercruiser

scarpint

Petty Officer 3rd Class
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Aug 25, 2008
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I've got a '88 Sea-Ray Sorrento (21' with Alpha One Outdrive). I've owned the boat 10 years and have never touched the plugs, wires, cap and/or rotor.. Up until this weekend, the boat has been parked next to the garage (appropriately covered and winterized). Given some other cooling challenges I've had with the boat over the weekend, and the fact that the motor simply stopped while I was out on Fridayn night past (wouldn't start after this happened, but when I got it in the garage a couple of hours later, it did fire up and also ran for 15 minutes in the driveway today).

I have no idea why it quit running, but I thought it best to do a "tune up". I've got several questions.

  • Should I stick with all Mercruiser OEM pieces/parts for all the components I referenced above?
  • If not, any thoughts on suitable replacement
  • I have a new fuel filler, so I wonder what else I should look at for a tune up?
  • Once I've replaced everything, does this motor required a timing adjustment?

I'm addressing some running hot issues in another thread, but I'm curious if I should be looking at anything else since I'm into it this far?

Thanks!
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
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19,084
Re: Tune up for 5.7L Carburated Mercruiser

what about the impeller, manifolds , thermostat, risers?
 

scarpint

Petty Officer 3rd Class
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Re: Tune up for 5.7L Carburated Mercruiser

Addressing the overheating issue in another thread. Thought it best to keep them seperate.
 

Failproof

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Re: Tune up for 5.7L Carburated Mercruiser

Mercruiser stuff is nice, but i use sierra tune up kits that I-Boats or west marine offer. If its been 10 years, do the plugs (carefully as 10 years of rust is a lot) wires, cap, rotor, and rebuild the carb. New fuel lines are also a good idea if you have ethanol blended fuel and lines are that old. All the filters (in carb too if it has them) and clean the intake arrestor. Another thing to look at would be exhaust flappers. How long since outdrive has been off?
 

Silly Seville

Senior Chief Petty Officer
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Dec 5, 2009
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Re: Tune up for 5.7L Carburated Mercruiser

Your plugs are AC Delco MR43T. DO NOT be talked into Champion, Bosch, Motorcraft or any other nonsense. Trust me! Wires are anything that is 8mm double/triple silicon jacketed (heavy duty), Cap and rotor definitely use Merc/Sierra. If your carb is a Rochester Q-jet, don't forget the tiny cylindrical fuel filter that is in the body of the carb. As Failproof said, definitely get new (marine approved) fuel lines, and DOUBLE CLAMP!

It may also be time for a new ignition coil. That may very well be your stalling issue, among the obvious above mentioned items. I personally think your distributor cap contact points are corroded or pitted/burned out, along with the rotor tip.
 

Oshkosh1

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Jun 8, 2009
Messages
968
Re: Tune up for 5.7L Carburated Mercruiser

It may also be time for a new ignition coil...I personally think your distributor cap contact points are corroded or pitted/burned
Plugs/cap/rotor...I don't think that motor HAS points.

CHECK your wires using a meter. You should see approx 1k resistance per inch of wire. If they're close...they're good. Give the terminal ends a coat of dielectric grease prior to reassembly.

Coils usually either work or they don't...probably not an issue to worry about. The stalling is probably a maintenance(or lack of) issue, not a part failure...in the true sense.

If it's been that long, I'd consider taking a good look inside the carb too.

Set the the timing. After that, idle mixture and idle speed.

The double clamping is a must...

Handle the cooling issue, and back to sea!
 

Silly Seville

Senior Chief Petty Officer
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Messages
798
Re: Tune up for 5.7L Carburated Mercruiser

I don't wish to start an argument with you Oshkosh, but the OP stated that the engine has not been tuned up in ten years. While testing the wires may be a great money saving endeavor...replacing them with brand new has its merits as well. I would also like to state that it is an incontrovertible fact that an ignition coil CAN go bad slowly over time...I have experienced this on two of my old cars, and more recently on my bowrider. The windings of the coil begin to crack and lose continuity, and as such increase in their resistance until spark is reduced to the point of stalling the engine. Coil cools off, windings relax/contract and you're off and running for a time until things get hot again. I'm not saying that it IS the coil, only suggesting that again, for a few dollars, why not consider replacing potentially decades old parts with new when it is easier to do than be towed back to port?

BTW, to address what you said about his engine not having points...I was referring to the brass points of contact inside the distributor cap that the leading metallic edge of the rotor hits as it passes around inside the cap. Sorry for those who may have misunderstood. Maybe I should have called them contact terminals.

Anyway, carry on!
 

Failproof

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Re: Tune up for 5.7L Carburated Mercruiser

As far as plug wires are concerned; my view is this. We spend extra on all the spark arresting junk on starters, alternators, and blowers, and trim pumps. Here are the plug wires, carrying 30,000 to 50,000+ volts of SPARK! Sure they may meter out, but one slight cut or crack in the housing, and you have a potential source of ignition in the one place we spend extra trying to prevent it. 10 year old silicon or extruded rubber wires are gonna be more prone to arching. Same with the coil, at its vintage, its more likely to have an arch line, micro cracks, and such. Just one dudes oppinion.
 
Joined
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Re: Tune up for 5.7L Carburated Mercruiser

Here is a page from the manual with the 2-different kind of distributors. The Mallory with points, and Thunderbolt lV which is electronic.

Pull off one of the wires and see which type of cap you have.
 

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Oshkosh1

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Re: Tune up for 5.7L Carburated Mercruiser

I don't wish to start an argument with you Oshkosh

Hey...no worries

I personally have never had a coil that was "going bad", I've had them "go bad" in sleds/cars, as in NO spark. And the wires, same thing. The only "bad" ones I've had were tested, and either tested waaay out of spec, or lit up like a christmas tree in the dark so were replaced. The wires/coils on my 40 year old snowmobile are original...(along with everything but the plugs/points)never saw the need to replace them(you can't...without replacing the coil too) just for their age.

Everyone's got their own "method to the madness":D
 
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