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  1. #1

    Default 5.7 mercruiser timing

    I have a 1995 5.7 mercruiser straight inboard. I want to check the timing. It seems that that some distributers need to be grounded and others do not. How can I tell what ignition system I have. There are two wires (nut and bolt terminals) on the distributer, no other electronic goodies. It is a quadrajet carbed engine. Thanks.

  2. #2
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 5.7 mercruiser timing

    You have a Thunderbolt IV ignition. You do not have to put it in base timing mode. Just hook up your timing light and look at the timing.
    Go up to the adults only sticky, and go to the Merc service manual link and download manual #17. Has all the info you need.
    Don S.


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  3. #3

    Default Re: 5.7 mercruiser timing

    Thanks for the adults only area. Great resource! Went to the boat this morning timing light in hand and gave it a shot. Runs like absolute crap at 8*BTDC. When I set timing by ear, motor runs great More RPM's, starts quicker, sounds more confident.However, according to the timing light I am at +-10*ATDC. I say again though, that is where the engine runs absolutley fantastic. I am using the dash tach at 650 rpm's.

  4. #4
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    Default Re: 5.7 mercruiser timing

    the reason it runs like crap at 8 BTDC and good at the 10 ATDC is no timing it i probably it has been so long since you have done a tune up or... your fuel delivery is off.

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  5. #5
    Supreme Mariner bruceb58's Avatar
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    Default Re: 5.7 mercruiser timing

    Are you sure you are on #1? Looking at the engine, which wire did you put it on?
    1998 Wellcraft Eclipse 24 Cuddy
    Volvo Penta Duo-Prop 7.4L "LK"

    2006 Sun Tracker Party Barge 21
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    "Common sense is not very common"
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  6. #6

    Default Re: 5.7 mercruiser timing

    Gentlemen I'm pretty religious with maintainence. Two spin on fuel filters and the carb filter are new. Plugs cap rotor this year. Fuel pressure/pump bad?
    That I dont know, haven't guaged that. Runs strong at "wrong" timing. Last season and this season had a dieseling problem that yard mechanics couldn't work out. They said timing was right on and i didn't pursue it because a shot of fuel treatment made the dieseling go away. Now I'm the yard mechanic (well kinda sort of) and I can also say timing was right on, but its like a new engine at 10* ATDC. It's a fishing boat and I dont speed in it. However I know timing is important and dont want to hurt anything. Carb rebuilt this year also. Thanks.

  7. #7

    Default Re: 5.7 mercruiser timing

    If I manually line up the mark on harmonic balancer with O* on tab and then remove distributer cap the rotor should be pointing to #1 plug. If it's pointing elsewhere how much trouble am I in. Thanks and enjoy the weekend.

  8. #8
    Supreme Mariner bruceb58's Avatar
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    Default Re: 5.7 mercruiser timing

    You have a 50/50 chance that it is aiming at the right plug. Turn the crankshaft amother 360 degrees and report back. Remember, you have a 4 stroke engine. Crank rotates twice for every revolution of the distributor.
    1998 Wellcraft Eclipse 24 Cuddy
    Volvo Penta Duo-Prop 7.4L "LK"

    2006 Sun Tracker Party Barge 21
    Mercury 90 4-Stroke FI
    "Common sense is not very common"
    "Failing to prepare is preparing to fail." -- John Wooden

  9. #9
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 5.7 mercruiser timing

    If you time an engine by ear, thinking that the faster the idle and smoother it runs, you are WAY OFF THE MARK.
    Put the timing at 8 BTDC at 650 to 700 rpm. Then adjust the carb for best idle. It's usually done after replacing the spark plugs, cap and rotor during the seasonal tuneup.
    You should also be doing a yearly compression check just to make sure the engine is actually tunable.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  10. #10

    Default Re: 5.7 mercruiser timing

    Still working on my timing issue. I have verified top dead center on compression stroke with a wooden dowel in #1 spark plug hole. The mark on harmonic balancer lines up with 0 on timing marker. Rotor is pointing to #1 wire on distributer. Can"t get any happiness at 8*BTDC but at 10* ATDC runs good at idle and up. Any other suggestions? Thanks.

  11. #11
    Rear Admiral 180shabah's Avatar
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    Default Re: 5.7 mercruiser timing

    is it tbiv or tbv?

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