Mercury 115 Help

[mwinchel]

Hey Everyone,
I have a 1971 11150 mercury inline 6 motor and i have a few questions. First is my wide open throttle is about 3500 rpm does anyone knwo why. When i look in books it says it should be 5500 rpm. My other question is i have a 2 blade prop on it i think that is factory. Should i put a 3 blade and what size and pitch do you recomend?
My last and final question is when i pull away from the dock and get going it seems like the first or second big wave i hit the moter will bog down and we will slow to a stop a then it will cut off. I will then pull my warm up lever up and crank it and go again maybe never to have a problem till later in the day when i crank it after it has been sitting and is cold again. When i am going accross the lake pretty good i get greedy and give it a little more gas and it will pick up and go for 30 sec or so and then bog down and i will have to stop and start again. What does this sound like if i just get at a good cruising speed and maintain it and never give it any more gas i will be fine.

I have replaced all the gaskets in the carbs, the 2 fuel pump diaprams, and the fuel line going from the fuel tank to the front of the motor. Can anyone help with my problems any info would be nice thanks.

 

[Droll]

Re: Mercury 115 Help

Hey Everyone,
I have a 1971 11150 mercury inline 6 motor and i have a few questions. First is my wide open throttle is about 3500 rpm does anyone knwo why. When i look in books it says it should be 5500 rpm. My other question is i have a 2 blade prop on it i think that is factory. Should i put a 3 blade and what size and pitch do you recomend?
**

Is this a new engine/boat ?? ( for you ) if not, did you retch the recommended WOT rpm before .

You need to get the rpm up , or you WILL damage the engine seriously.

If everything are ok and the only problem are the propeller, a propeller with less pitch will help.
To help you more with the estimate we will need more tech data about the boat ( size, weight, type ).
The current propeller size/type should also be provided .

To tune the engine, read this FAQ .



Arne Kjetil

 

[Barnacle_Bill]

Re: Mercury 115 Help

Check for a strong spark at all cylinders. What size prop is it?

 

[mwinchel]

Re: Mercury 115 Help

I am not sure of the size of prop. I do know it is a 2 blade prop and it looks factory to me. The boat is a 1971 manatee 15 foot with a 115 inline on it. The boat goes good but not good enought for me. I read all day long about how this motor is the TOWER OF POWER and i think mine should have some more gitty that is holding it back. When i received this boat i went threw all the carbs before i even hit the water so that may be an issue. I am not sure how it ran before but i was told it could pull 2 skiers out of the water. Let me know what you all think. I put new wires on it but it has a stupid screw in terminals in the distributor. When i changed the wires the terminals were nasty and barley crimped on to the wire so i oreded new ones of those so that may have something to do with it. let me know if there is anything eles you can think of. It is tri hole.

 

[Barnacle_Bill]

Re: Mercury 115 Help

Those wires could be you problem. But still check for a good strong spark at each cylinder after you replace them. That boat should fly with a 115 on it. Look on the prop for any numbers.

 

[Scaaty]

Re: Mercury 115 Help

Did you pull the distrubuter cap? Could be a real funky mess in there..

 

[mwinchel]

Re: Mercury 115 Help

I did take the distributer cap off there is nothing bad in there. I looked that prop tonight and all i seen was a 19 i am assuming that this is a pitch of 19. Like i said before this is a 2 blade prop should i get a 3 blade 19 pitch prop let me know. Earlier in this tread i was talking about when i gave it a little more gas it would go and then die out. I was looking at my engine today and the fuel line going to the top carb is pinched. I rememeber when i got this boat i had to replace that before i even took it out. Stupid question but could that be my problem at wide open throttle. The od of the line is .500 and with it pinched it is probably 3/8 or maybe a little smaller sounds like that could be a problem let me know thanks.

 

[Bt Doctur]

Re: Mercury 115 Help

check the compression on all cylinders
check for spark on all plugs

 

[Barnacle_Bill]

Re: Mercury 115 Help

A pinched fuel line can be bad news. Get it fixed and do a compression check as advised. Sounds like you need to check that motor over very carefully to see what else isn't right.

 

[Lone Duck]

Re: Mercury 115 Help

Check your tank vent.

 

[renny1]

Re: Mercury 115 Help

i would go and check compression as said above and then click on my name and read my "low compression thread" as all the symptoms you are giving is exactly the same as mine started
the rpm dropped to 4500 so i changed fuel lines,diaphragm gaskets new plugs cleaned carbs new gaskets spent ages trying to decipher what the problem was an then rpm went down to 3500 then i did the compression test which revealed number 3 was only 30 psi all the others were 120 and it ended up being a ceased piston ring which broke and killed the piston
anyway just read the thread

 

[mwinchel]

Re: Mercury 115 Help

Hey everyone i was going to let you get up to date on my little problems. Well after i read threw the tread renny and a couple of other people had me worried about my compression. I bought a compression tester yesterday from work and checked it out last night. I have between 120 to 125 psi in each cylinder. I think this is good but i am not sure what they are sopose to have. I also but new ends on my spark plug wires where they screw into the distributor cap. Last year i replaced the wires and i got the universal kit from a local parts store that are 8mm wires and they did not fit in the ends right. So i wedged them in there. But know i have new ends that fit great and a unpinched fuel line. Let me know what you all think. This is a 1971 motor.

 

[Yepblaze]

Re: Mercury 115 Help

I'd suspect that it may be starving for gas, and maybe dropping some cylinders.


Try having someone squeeze the primer bulb while it's acting up and see if the issue goes away.


Even though you changed the gaskets and a couple other fuel system components, it's still quite possible to be having fuel supply problems.

It may require that the carbs, fuel lines, filters, and or pump(s) be removed serviced, and inspected completely.

 

[Chris1956]

Re: Mercury 115 Help

You can pick up some OEM style spark plug wires for about $6 each if you look at either oldmercs.com or vintageoutboards.com(I forget which one) Look for the "Tiger Tails" which are 36" in length, and have the crimped on threaded end.

 

[bazzmaster]

Re: Mercury 115 Help

I've got the same motor, not sure about your fuel problems but I would definitley consider getting a 3 blade prop, you should have no prob running about 55 mph and have a better hole shot.....I would have to check my pitch and get back to ya to make a suggestion but any prop dealer should be able to give you the right specs......

 

[mwinchel]

Re: Mercury 115 Help

Hey there if you can get a free second can you look into that and let me know your pitch on your prop and if it is steel or alum. My 2 blade is a -19 i assume that means a 19 pitch. One other thing this is a little boat buti do most of the time have 5 people on it and a big cooler. So it is pretty weighted down and it is a tri haul boat. Let me know what you think thanks

 

[Yepblaze]

Re: Mercury 115 Help

As I have come to find, lower units from many models and gear ratios can fit on that motor.

confirm your gear ratio

Put it in gear, mark prop and flywheel with a little bit of masking tape, turn flywheel(by hand key off) and count the revolutions required to turn prop one full turn.



Once the ratio is confirmed, appropriate pitch can be addressed.

 

[Chris1956]

Re: Mercury 115 Help

Gear ratios on 115HP inline sixes are most always 2::1. Some inline fours (ie 850) had 2.3::1 gar ratios. A lot of this difference may be made up with a new prop

 

[Yepblaze]

Re: Mercury 115 Help

Not to steal your thread, just some insight.


And the ones from earlier models that fit up, are something like 1.75:1

I know this because after finding a replacement for my 76 1150, (2:1) and finding out the replacement was the higher (1.75:1) ratio, the prop search began all over again. And I'm not real happy about spinning a big dia. low pitch prop on that. A 15P cup is a bit much and a 13P flat slips and wastes gas like crazy.

on another motor...

I just changed out a mid lower on a 67 1100 to find out it was a (2.3) off a 4cyl. Boy that sucker spins nice and easy. I need to get the tach on it.


A lot can change in 30+ years

 

[daveswaves]

Re: Mercury 115 Help

Hey everyone i was going to let you get up to date on my little problems. Well after i read threw the tread renny and a couple of other people had me worried about my compression. I bought a compression tester yesterday from work and checked it out last night. I have between 120 to 125 psi in each cylinder. I think this is good but i am not sure what they are sopose to have. I also but new ends on my spark plug wires where they screw into the distributor cap. Last year i replaced the wires and i got the universal kit from a local parts store that are 8mm wires and they did not fit in the ends right. So i wedged them in there. But know i have new ends that fit great and a unpinched fuel line. Let me know what you all think. This is a 1971 motor.

A couple of things, first of all those 8mm wires are likely resistance wires for reducing EMI That ignition system will not fire those at higher rpm. Get solid wires. If you "went through the carbs" then you are going to have to do a link and sync, I think Arne sent you to the link for that. 19p is fine for that setup, but 5 guys and a beer cooler in a 15 foot trihull is gonna be like an elephant on a skateboard. 120 to 125 is ok on the compression, seafoam will likely perk it up a bit. Get the boat running right with just you in it.