Mercruiser Timing

[ekeef01]

I was hoping someone could give me the correct timing for my mercruiser. It is a '94 5.7L with a 4 barrel Holley 650 carburetor. My father in law and I have rebuilt the entire engine and are finally to the fine tuning. We have the timing set at 0 now and it is okay out of the hole but the engine still sounds like it is laboring, also under a load it tends to ping around 20mph. I have been told that I need my octane close to 100 could this be part of the problem? Thanks

 

[Don S]

Re: Mercruiser Timing

Do you have a Thunderbolt 4 or 5 ignition system. Makes a big difference. Neither one are set at 0?. Usually around 8 or 10? BTDC at idle rpm. But with a TB5 system, you have to put it into base timing mode to set the timing and adjust the carb.

PS: A Merc SN from the engine would help.

 

[mkast]

Re: Mercruiser Timing

I have been told that I need my octane close to 100 could this be part of the problem? Thanks

Why? Is the compression in the engine 12.5:1?

 

[maxxman04]

Re: Mercruiser Timing

octane rating usually dosn't matter unless your motor runs 9.75:1 compression. however the brand of gas and how long it's been sitting can affect it. and Don S. is 100% right. ignition type is a HUGE factor.

 

[Don S]

Re: Mercruiser Timing

I have been told that I need my octane close to 100 could this be part of the problem?

Be very careful of everything you hear or read. You just never know who is right and who is wrong.

I have always smiled at the saying "THEY SAID" ........ Yeah, but who is THEY and what are their credentials to say things.

 

[Bondo]

Re: Mercruiser Timing

Yeah, but who is THEY and what are their credentials to say things.

Ayuh,.... I didn't say THAT,... but I am one of THEM....

Credentials,..??..?? a 'puter,+ an Internet connection,..... What more does it take,..??

 

[Don S]

Re: Mercruiser Timing

Ayuh,.... I didn't say THAT,... but I am one of THEM....

Credentials,..??..?? a 'puter,+ an Internet connection,..... What more does it take,..??

And it comes back to us too.
But how many times have you heard on this forum when some one says "I heard" or "They said" and when the repeat it, it's just pure crap.?
I hear it at work every day.

 

[mkast]

Re: Mercruiser Timing

a 'puter

What does a golf club have to do with this?

I know, "You're rude!"

 

[Bondo]

Re: Mercruiser Timing

But how many times have you heard on this forum when some one says "I heard" or "They said" and when they repeat it, it's just pure crap.?

Ayuh,... "They" are just somethingelse,....
They know everything,...
They're everywhere,..
They've done everything,..
I know somedays,. I'd like to kick Their Azz....

I know, "You're rude!"

Heeeyy,.... I resemble that remark,...??...

 

[stevesoule1]

Re: Mercruiser Timing

I have set mine at 6-7 degrees BTDC AT IDLE . I have a 5.7L mercruiser with Edelbrock 600 cfm 4bbl double pumper. I have a heavy boat @4500lbs. Put your drive all of the way down when you set the timing. bring a friend who can safely steer the vessel, and a timing light, and play with it until you feel like it is operating to the fullest capacity. DO NOT GO MORE THAN 12 DEGREES BTDC!!!!! Also keep in mind that you want to tune the motor to stay in the torque band 3200-3850 RPM. I recommend running 93 octane because it stops predetonation, and burns more efficiently. SPEND THE EXTRA FEW DOLLARS AT THE PUMP, AND YOU'LL NOTICE THE DIFFERENCE. You might need to upgrade your ignition. Check the coil as well. I wouldn't worry too much about 100 octane unless your compression is over 11:1. Make sure your cylinders cancel when you drop them 1 by 1. check your wires, cap, rotor. you may need hotter or colder spark plugs according to engine operating temp.

 

[mkast]

Re: Mercruiser Timing

and play with it until you feel like it is operating to the fullest capacity. DO NOT GO MORE THAN 12 DEGREES BTDC!!!!! I recommend running 93 octane because it stops
predetonation,

Can you show me where in a Mercruiser maintenance manual this information is stated?
I have heard of pre ignition, an I have heard of detonation,
what is "predetonation"?

 

[Don S]

Re: Mercruiser Timing

I have set mine at 6-7 degrees BTDC AT IDLE . I have a 5.7L mercruiser with Edelbrock 600 cfm 4bbl double pumper. I have a heavy boat @4500lbs. Put your drive all of the way down when you set the timing. bring a friend who can safely steer the vessel, and a timing light, and play with it until you feel like it is operating to the fullest capacity. DO NOT GO MORE THAN 12 DEGREES BTDC!!!!! Also keep in mind that you want to tune the motor to stay in the torque band 3200-3850 RPM. I recommend running 93 octane because it stops predetonation, and burns more efficiently. SPEND THE EXTRA FEW DOLLARS AT THE PUMP, AND YOU'LL NOTICE THE DIFFERENCE. You might need to upgrade your ignition. Check the coil as well. I wouldn't worry too much about 100 octane unless your compression is over 11:1. Make sure your cylinders cancel when you drop them 1 by 1. check your wires, cap, rotor. you may need hotter or colder spark plugs according to engine operating temp.

Sundays are wonderful, all the newbe experts register and come out of the woodwork with all this wonderful, over the top information

 

[cannonford57]

Re: Mercruiser Timing

yep,the type ign would be helpful....it determines if a shunt needs to be used or not....can be helpful.and if 6 or 8 or 0 degrees is needed.shoot,i've hung off the fender of a buddys truck "twisting' dist.while he barreled down the road till the manifolds achievied the proper shade of cherry red,but t hats another story........and another time.heck its the 90's,I mean the 2000's......right.and of course we're talking marine applications.sorry,had a moment.......

 

[Searay23]

Re: Mercruiser Timing

Do you have a Thunderbolt 4 or 5 ignition system. Makes a big difference. Neither one are set at 0?. Usually around 8 or 10? BTDC at idle rpm. But with a TB5 system, you have to put it into base timing mode to set the timing and adjust the carb.

PS: A Merc SN from the engine would help.

Newbie here to the forum.. Question: How do you tell what kind of ignition you have.. I have '93 Searay, 5.0LX GM, 4 barrel, mercruiser. I want to check my 8* timing and been reading here about jumper wires, etc.. Also, on the notched timing tab, is each of the notches 4*? Need a procedure to follow.. thanks.. Clint
PS: Eng S/N: OF013756

 

[Don S]

Re: Mercruiser Timing

Starting a new thread is the first thing you need to do.
Don't start your question at the end of someone elses old thread.