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Merc 50L Spark advance

S

S. Wiley

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"Merc 5.0L vintage 2001 engine

"Merc 5.0L vintage 2001 engine w/ Rochester 4 bbl.

I think I have a problem with the spark advance. II have not looked, but believe this has a mechanical advance? If so, can I visually inspect the distributor to determine if it is working?

Symptoms - The boat has a hard time getting up on plane, and the engine does not seem to rev appropriately when the the throttle is openned up (Prop pitch is correct = 18). If this were my V-8 in my Cuda, I would be suspecting a vacuum leak, spark advance, or timing (carb seems to function appropriately).

Any diagnostic tips would be greatly appreciated."
 
"You should check your timing

"You should check your timing since guessing won't work. If you want to test the advance, run the motor with a timing light on it and watch for advance to increase with RPM increase. I doubt it's a mechanical advance but I don't have one in front of me. You have the Thunderbolt ignition and IIRC, that's a vacuum advance.

What kind of boat is it, what is the RPM at WOT and what is your top speed? When was the last tune-up, was it a full tune-up or did you omit things like plug wires, cap, rotor, plugs (because they looked fine), clean flame arrestor, etc?"
 
"if its a vac advance, you may

"if its a vac advance, you may want to put a vacuum pump on the advance tube as you watch the timing light. Dont know, but would expect 2001 to be all electronic."
 
"Yes - Thunderbolt ignition. S

"Yes - Thunderbolt ignition. So if vaccum advance, where does the Merc setup have the vacuum hose running? (From port at the base of Distributor to a vacuum port located.....where?? Or is this totally off base?)

WOT has RPM of around 4300 and speedometer reads around 35-40 mph. Last tuneup was plugs only. Flame arrestor is clean as a whistle.

The boat is up at our camp, so I will need to be armed with as much info as possible before traveling."
 
"If it has vac advance, the li

"If it has vac advance, the line will generally go from the disrtibutor to a port on/under the carb, below (after) the throttle plate. If it's mechanical advance, it's internal. Check the timing while increasing the RPM or we're just guessing.

Did you hit anything with the prop?

What kind of boat is it?

Plugs only is NOT a tune-up. Your boat is about 5 years old and plug wires are good for about three. Cap and rotor are good for about the same unless it was run under high load a lot or if it is stored in a high humidity environment.

First thing I would do is take a fuel sample. If it sits for long periods and you use gas with ethanol, the gas has water in it, maybe worse. If it's old gas, it will have a distinctive odor, totally unlike fresh gas. The octane will also be lower than it should be and this will contribute to the loss of power."
 
Boat = Celebrity 20 ft.

Not

Boat = Celebrity 20 ft.

Nothing hit with prop.
No ethanol. New gas too.

Another post thought this engine w/ Thunderbolt ignition would not be mechanical advance????
 
Are the plug wires for Marine

Are the plug wires for Marine application different from high end automotive wires?
 
"Don't know the official a

"Don't know the official answer but I wouldn't hesitate to put automotive wires on a boat engine. Just so you, some wires are junk. Stay away from Beck Arnly or cheap aftermarket. NGK, Taylor makes great wires."
 
"I like the 8mm Taylor silicon

"I like the 8mm Taylor silicone wires. I worked on Mastercraft boats for quite a while and they have used them for a long time. Never had a problem with them. I like the NGK plugs when applicable but haven't used their wires. Always used NGK plugs on outboards, PWC, some sterndrives and inboards.

I agree- cheap wires aren't worth the trash can they go into. If you want to stay with Mercruiser or AC Delco wires, you should be fine. I wouldn't recommend the make-'em-yourself kit, though. Mark the distributor cap for #1, write the firing order and rotor rotation direction down, label the plug wires and take them in so you can get a direct match. When you put the new wires on, mark them so you know which goes where and if the new cap is marked for #1, you'll have less trouble with the firing order (which should be cast into the intake manifold) in the future."
 
If you find a vacuum advance o

If you find a vacuum advance on the boat please take a picture and post it.
I've never seen one in a boat made after the 70s unless someone put a automotive distributor in it.
 
"I'm still wondering why t

"I'm still wondering why there's debate about the advance when it hasn't been checked yet. I would hold off on any repairs until the diagnostics have been done. This could be a fuel quality/flow issue, spark intensity, cap/rotor/plugs/wires issue, etc. First thing I would do is verify base timing and go from there.

If the distributor was replaced with an automotive one, it needs to be changed back to marine- marine is made to not cause any kind of spark and when there are combustible fumes (as there are most of the time) in the bilge, an explosion is prevented."
 
"ok.....So I have to know how

"ok.....So I have to know how to determine what I am really dealing with here. What can I look at on the distributor, on this marine application, to identify the type of ignition advance?

There are posts here that say both it can't be vacuum, and it's not mechanical.

thanks everyone."
 
It's mechanical.
There a

It's mechanical.
There are flyweights under the pick up plate in the distributor. Check that all parts are moving free.
 
Thanks Charli - that makes se

Thanks Charli - that makes sense from what less than expert knowledge I have. You don't happen to know the timing/rpm settings for this engine?

Thanks.
 
Are you at sea level? If so ti

Are you at sea level? If so timing 8 BTDC. RPM- idle 650-700 but 600 is ok. 4200-4600 top RPM.
Myself I try for 4500 RPM at wide open with small load(full of fuel two people).
 
"You might want to call a deal

"You might want to call a dealer and find out how much total advance you should see and what the advance should be at various RPM. If base timing is good but the advance at 2000 RPM is excessive, the springs may have relaxed and should probably be replaced. If you pick their brain, you should be able to get some additional info about your distributor. Make sure you have the motor serial number handy because they'll almost always ask for that in the beginning of the conversation."
 
"1st, Tbolt IV and Tbolt V do

"1st, Tbolt IV and Tbolt V do not have vacuum or mechanical advance. There is a Hall Effect switch in the dist. Advance is controlled by the ignition module. The lead timing is set at idle Normally 8 degrees. The engine specs listed on the engine will tell lead timing. Advance on tbolt ign. is normally all in by 2500 rpm. usually 26 degrees.

I recommend a timing check at 2500 rpm and a compression test."
 
""All in"? are you a p

""All in"? are you a professional gambler?

Thanks for the reference to the Hall effect sensor- I had forgotten about that even though I was talking about timing a Mercruiser and how the IC module receives the RPM info, not long ago. DOH!"
 
Actually no. The term "al

Actually no. The term "all in" in reference to total timing has been around longer than no limit hold em has been popular on tv.
 
"Might be a regional thing- I

"Might be a regional thing- I have only heard it called "total advance", but I guess it depends on who is talking about it."
 
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