Max RPM's and Care for the In-line 6 Cylinder Mercurys

[David CVX-16]

This advice from Thom "Dr. Frankenmerc" an expert Mercury mechanic, posted on the FiberGlassics Mercury Outpost:

"I run my '77 1500 at a constant 6000 with max timing at 20 BTDC with ethynol 92 octane and 50:1 AMSoil.
I run my '87 115 to 6300 constant - BUT no,...I don't recommend it.
My formal recommendation for both would be 57-5800 with a maximum wide open throttle timing set at 20 BTDC on any inline-6 built after 1970. (or in other words,...Any with direct charge pistons)
Proper oil and the best gas you can find at a proper ratio with periodic use of a de-carbonizing agent to keep the rings and domes clean is critical.
If you compression readings aren't good or you don't know the true condition of your rings and domes I would red-line at 56-5700 and mix 40:1 AMS or Quicksilver semi-synthetic.
I strongly recommend installing a fuel filter/water separator with a clear bottom section and petcock and monitor it very frequently when running today's ethynol.
Install the filter between the prime bulb and the engine.
(others may suggest install between the tank and the prime bulb, but between the prime bulb and the engine is what was recommended to me by several CMTs. (Certified Marine Technicians)
I also recommend use of Star-Tron or Stabil Marine and a decarb agent like Sea Foam or OMC Engine Tuner.
Star-Tron or Stabil Marine (blue fluid not red) every tank and de-carb every other tank of fuel mix.
These old beasts will perform very well when properly cared for.
Impeller replacement every year or two max is critical due to the crummy design of the impeller."
        

[badgercarlson]

I've never used Sea Foam in my '77 1150.  What is it?  What does it do?  Should I use it?  What difference will I notice in the performance of the motor?  I guess I'm a dummy when it comes to understanding the effects of carbon build-up.

[Jason]

Is this the Amsoil he is talking about?

http://www.amsoil.com/storefront/ato.aspx

[David CVX-16]

Jason, if you go to this website, Amsoil makes four different marine oils, one appears to be for 2 cycle snowmobiles, motorcycles, personal watercraft, ATVs and jet boats, one for racing for short periods of times, another for DFI outboards, and the last is Saber, which is their standby 2 cycle outboard motor oil. I have never used Amsoil because my RPMs have been limited to 5,300 to 5,400 for short periods of time. Dr. Frankenmerc does not say which type of Amsoil he means, but I bet it is the Saber. Amsoil says that Saber can be used in 100 to 1 ratio, but Dr. Frankenmerc would use it at 50 to 1 or 40 to 1. He also mentions Mercury semi sythethic, which is the Mercury Premium Plus, which I use in a ratio of one pint to 5 3/4 gallons of gas.

http://www.amsoil.com/storefront/synthetic-powersports-boat-oil.aspx

It is interesting that he recommends only timing of 20 degrees before top dead center, as my Mercury's decal on the motor says 23 degrees. The thought is that with aging motors with carbon deposits, worn rings, crummy gas, to error on the conservative side -  20 degrees BTDC. A blow to performance but a plus to the engine's life.

Seafoam is a solvent that can be added to the oil, gas, and sprayed into the combustion chamber to dissolve carbon deposits, which build up on the top of the pistons and in the rings and cause damage because carbon retains heat and can prevent the rings from expanding.

[Hyperacme]

At the end of the season I change oil in LU and dump some Sea Foam in tank, depends how much gas/oil is left in tank but put a pretty good amount in.
I pull the plugs and tilt motor all the way up, turn flywheel until top piston is at TDC and spray Deep Creep ( which is Sea Foam in a spray can ) into and around edges and down in to ring lands, let sit a min. or two then bring down piston and squirt into exhast ports.
I do the same with the next two cyls. ports & pistons.  Let sit about an hour then do it again.  Let sit another half an hour to hour.
Put plugs back in and start it up ....Filling neighborhood with white smoke ... LOL

What ever is the main ingredient in Sea foam it is a solvant that softens up carbon on your piston, around your rings and in your exhust ports and crap in your fuel system.
I think oil injection would run your oil mix at 100 to 1 at idle and about 50 to 1 at WOT, but with pre-mix your running it at 50 to 1 all the time so you get more carbon build up ... maybe ...

If your motor has never been done, as my motor had never been done when I got it ... you might want to do it twice, making sure to get lots in exhast ports.
Ya should get lotsa googy black stuff coming out your prop exhast with bilowing white smoke to impress your neighbors ... LOL

Carbon can create hot spot on pistons and make sticky rings.

[MarkS]

Photo originally posted on CGOA;
Photo courtesy MarkS' Starflite  But just for "the record", if Dr. Frankenmerc says 20* is plenty, that's where I'd set mine.    That man KNOWS his Mercs!

[badgercarlson]

Just looked at the Sea Foam website.  Some good info about Sea Foam and what it does.  Says it also stabilizes fuel for 2 years.  I'm going to try it. 

[David CVX-16]

Mark, great picture of the water separator. Becomes more critical the longer the gas sits in the tank.

The First Baptist Church sign arrow has it as "prop for greater than 5,500 wide open throttle", whereas the arrow should point the other way meaning "less than".
  

[Jason]

There are not to many magic "fixes in a can" but Seafoam is one of them. Took a lifter tick out of an old Pontiac i had and Transtune took a slip out of the tranny in my dodge truck.

[MarkS]

Yup David, they got the "<" sign backwards on the church sign, good eye.  I know some guys run 'em up to around 6000 too, but I think Doc was talking about max longevity in his statement, not fulfilling the "need for speed" quest.   

I had heard so many horror stories about the methanol in our gas, I thought the separator would be a good idea.  I don't let my gas get "stale" very often, more of a preventive measure than anything.  Plus I like the idea of 1 micron spin on easy access filter before the gas ever gets to the motor.  I still use the StarTron in every tank, and just started using SeaFoam recently.  I figure any help you can give the old girls will pay off in the long run...........?

[Glastron_GT160]

That sign ">" is correct.  I believe, the intention there is not to over-prop the motor which does a lot of damage.  I guess the point is you want to have WOT RPM above 5500rpm, but not necessarily run at that rpm all the time.   Lugging an inline motor with too much prop pitch makes piston sized paperweights

[Jason]

I wonder if he would recommend the same settings for a 1967 950SS inline 6...........

[David CVX-16]

Jason, here are the specs for a 1967 950SS, although they are said to be unverified:

http://www.piranha.com/motor_specs.php?id=3855

Manufacturer: Mercury
Model: "Merc 950SS; Model 950SS"
Year: 1967
Horsepower: 95.0
Cylinders: 4
Type: 2 stroke
Gear Ratio: 1.78:1
Min WOT RPM: 4800
Max WOT RPM: 5200
Spline Count: 15
Drive Type: Outboard

******* Note *******
Double check values In Red as they have not been verified on this model.

In general, the Max WOT RPM's for a 150 HP Merc are higher than that of the 95 and 115 HP. The recommended Max on my 1974 115 HP is 5,300, and 5,500 for the 1988 115 HP.

[Jason]

I thought that is what I saw before. Around 5200. Glad I didn't bring her up to 6000!