1979 Mercury Inline 6 115hp

**bestman53** · 07-07-2020, 09:33 PM

I have a 1979 mercury inline 6 115hp and would to pick the brains of this forum about upgrades, performance tweaks, and just general knowledge to make me more knowledgeable of this remarkable engine.

First question, there is a small hose that goes from the top of the carb float to the a fitting on the side of the carb. In the parts breakdown, its called an Economizer hose. I've heard of people removing this hose and plugging the fittings. Do you plug both the float and carb fittings? What do you do with the jet on the side of the float?

Second question, there are three fittings and two hoses that are on the crankcase/cylinder block area, just behind the carbs. In the parts breakdown it is called the Main Bearing Balance Hose. What do these actually do?
My engine did not come with a Enrichener solenoid to help with hard starting, and i heard of people adding one to their engine and tapping into one of these Balance Hoses. Is this true?

As I come up with more questions ill add to this post.

thanks again for any knowledge that is pasted down.

**rhardwick** · 07-08-2020, 06:48 PM

1979 was probably the last year of the choke butterflies. Old trick we would do would be to tilt the engine all the way up, pump the primer bulb until you see gas in the splashwell and trim down and start the engine. The age of the engine and loss of base compression plus the butterflies did a poor job of sealing the air from the carbs. You can adjust the butterflies some to make a better seal.
The enrichener took fuel from the top carb and connected to the balance tubes to help with cold starting. Look up mid 80's 90 or 115 to see how it works.
Not much you can do unless you go into it, ports can be played with both intake and exhaust. With a can block you would have to replace the pistons to help any. Best option would be to find a 1985/1986 115 block that is power ported, those engines are prop shaft rated HP with around a 140 powerhead. Better yet would be to find a 1500XS or 1500 J powerhead and go from there. Those are distributor engines and maybe you can find a T2X timing disc to help the performance. Chris Carson has plastic reeds that would help but the inlines did not have a history of breaking reeds. A 1500XS with 100LL av gas will turn 7K all day!
Good luck

**1978allison** · 07-08-2020, 08:30 PM

Originally Posted by rhardwick

1979 was probably the last year of the choke butterflies. Old trick we would do would be to tilt the engine all the way up, pump the primer bulb until you see gas in the splashwell and trim down and start the engine. The age of the engine and loss of base compression plus the butterflies did a poor job of sealing the air from the carbs. You can adjust the butterflies some to make a better seal.
The enrichener took fuel from the top carb and connected to the balance tubes to help with cold starting. Look up mid 80's 90 or 115 to see how it works.
Not much you can do unless you go into it, ports can be played with both intake and exhaust. With a can block you would have to replace the pistons to help any. Best option would be to find a 1985/1986 115 block that is power ported, those engines are prop shaft rated HP with around a 140 powerhead. Better yet would be to find a 1500XS or 1500 J powerhead and go from there. Those are distributor engines and maybe you can find a T2X timing disc to help the performance. Chris Carson has plastic reeds that would help but the inlines did not have a history of breaking reeds. A 1500XS with 100LL av gas will turn 7K all day!
Good luck

What is the performance gained by using the T2x disc.

**rhardwick** · 07-08-2020, 08:47 PM

The T2X timing disc has larger windows and changes the timing. More suited for the 6 carb setup but a little performance gain on 1500.

**Mark75H** · 07-09-2020, 05:00 PM

How does a larger window change timing? Isn't the trigger activated by the window passing the sensor?

**Mark75H** · 07-09-2020, 05:07 PM

Another question: what is the point of running a motor 1200 rpm above its power peak?

**rhardwick** · 07-09-2020, 06:37 PM

Originally Posted by Mark75H

How does a larger window change timing? Isn't the trigger activated by the window passing the sensor?

The T2X timing disc has balanced timing, if you notice a stock 1500 timing disc the windows are offset. As mentioned above it's more suitable for the 6 carb setup but there is a little performance gain on a stock engine

**rhardwick** · 07-09-2020, 06:45 PM

Originally Posted by Mark75H

Another question: what is the point of running a motor 1200 rpm above its power peak?

Are you serious? I raced a 16' Allison in JP class in the late 70's. I was running 26-28" cleaver propellers (depending on length of course). On that boat I would have to run a 32"+ pitch propeller to keep the RPM to 5800, the boat would be a pig as it would take 2 miles to get it up to top speed.

**Mark75H** · 07-09-2020, 07:20 PM

Yes, for acelleration on a race course, higher than peak rpm is called for. Sacrificing a little top speed for getting off the corners quicker is what wins races. As someone once famously said, its not who's fastest that wins a race, its who's "firstest"