1984 115 hp compression ????

[caldog101]

just bought a 20 foot seacraft,with a 1984 115 hp mercury,I was really interested in the boat only and did not pay much attention to the motor turns out the motor is in great shape seems like low hours "no rust" Nd runs great But i would like to know what the compression should be for this motor it is a straight 6 thank you alos it does not have a tach so what maximun rpm should i get from this thanks again

 

[timmathis]

Re: 1984 115 hp compression ????

Test and post the compression. You would like to be in the 125 - 135LB range I would say. Tim

 

[andy6374]

Re: 1984 115 hp compression ????

Those numbers would be great, but it is more important that they are in the same range. No more than 10% difference between any of the compression valves. Make sure you take the compression after the motor is warm. Take notice of how many cranks it takes to get a certain compression value. In other words, if takes one cylinder 3-4 revs to reach 115 and it takes another 8-9 revs to reach 115, then you might have a problem and a leak down test is in order.<br /><br />But all in all, get it warm, do the same amount of revs per cylinder and make sure the are within 10%.

 

[caldog101]

Re: 1984 115 hp compression ????

Thanks guys,I will do the compression test this weekend and post the numbers the last time i did a com. test on an evinrude 4 cyl. i removed all the spark plugs wires from the spark plugs and then took one plug out a time to do this test i gather it's still the same also any idea what the max. rpm range for this motor thanks again

 

[andy6374]

Re: 1984 115 hp compression ????

I was always told to take out all spark plugs before taking a compression reading. I was told it could damage the gauge and I always just accepted that. Now, thinking about it, I can't think how it could damage the gauge.

 

[Clams Canino]

Re: 1984 115 hp compression ????

It'll spin over better with all the plugs out. If you don;t know it's history de-carb it ASAP and make sure you perform the full annual maintenance on it before running it. Those are a great outboard - if properly set-up and maintained.<br /><br />-W

 

[caldog101]

Re: 1984 115 hp compression ????

Thanks guys<br /> I will test it this motning with all the plugs out ,i bought the seacraft just for the boat and only glanced at the motor,but after taking it home and opening the cowling,I noticed the great condition of the motor,apparently the older gentleman "92"i bought it from had not put it in the water in 6 years but would start it every month religously until about 8 months ago was the last time he started it ,there is no rust and it looks like the lower unit was never taken off,i have taken it out 2 times and after a small hickup after a mile out for a minute or 2 it has run great,first run got up to 23 mph after adjusting the trottle cable got up to 27 but i think the prop is spinning " Clams " why do you consider them great outboards?

 

[Clams Canino]

Re: 1984 115 hp compression ????

Originally posted by caldog101:<br /> " Clams " why do you consider them great outboards?

Mercury marine built it's empire on the strength of two outboarbs: The 44ci "Super thunderbolt" and the 99ci "Tower of Power". You have the latter, at the final stage of it's evolution. Properly treated, that motor (in fresh water) outta outlive you.<br /><br />-W

 

[caldog101]

Re: 1984 115 hp compression ????

COMPRESION TEST RESULTS from top cyl.down<br />120<br />120<br />128<br />128<br />128<br />127<br />I was by myself so these are pretty close to within a couple of pounds"had to turn key and try to observe the gauge myself"<br />I would like to know what my next step should be. <br /> Right now the 20 ft seacraft will do 27 mph with this motor,But according to the spec. sheet with this set up i should be close to 40 mph,It did not come with a tach so i don't know what rpm it is turning,but i also know that the motor is not winding all the way out,please let me know how the compr. # look and if it worth spending time and money on it,such as carb,rebuild or decarb, etc...

 

[timmathis]

Re: 1984 115 hp compression ????

Compression is good. I would do a decarb it cost just a few dollars and a tune up. Just run it a few hrs with some seafoam and you may be lucky and not have to do a carb job . You can make a mark on the prop and hub with a marker to see if it is slipping. Sounds like you have a good old merc. Tim

 

[Clams Canino]

Re: 1984 115 hp compression ????

Yep..<br /><br />-W

 

[caldog101]

Re: 1984 115 hp compression ????

thanks guys <br /> ? about the seafoam. is it a liquid that you put into the gas or a spray can like the " omc engine tuner " that you spray into the carbs and if it is a liquid how much should i put per gal. of gas.I have cleaned out the gas tank "gas sat for about 8 months" smelled a little bad but i thought it would have been worst. so it is empty right now. thanks again for all your help and i will post a follow up on the performance OF this MERC. this is great forum i can sit here all night reading all this valuable imformation you people bring to this site.We all that ask for help from the more knowlegable people in this forum appreciate it greatly

 

[andy6374]

Re: 1984 115 hp compression ????

Get the aerosol can. Actually called Seafoam "Deep Creep", OMC engine tuner and Merc. Power Tune are similar products. FAQ decarb, tons of posts.<br /><br />The liquid is for maintenance purposes. With it, you can go much longer w/out a decarb and carb cleaning (assuming your carbs are clean from the begining).

 

[timmathis]

Re: 1984 115 hp compression ????

To clean out the fuel system tank,carb's, lines,Etc you will need the seafoam liquid in a can. The deep creep is more for the decarb Job.<br />I would use both to it at first and it is a good idea to use a little seafoam all the time to help keep it clean and stable. Tim

 

[caldog101]

Re: 1984 115 hp compression ????

Thanks Tim<br /> I looked up the"decarbing" in the engine FAQ section,I already bought the seafoam, deep throat and for the gas tank,and will do it this weekend,It looks like the engine has not been run at all.The gentleman i bought it off is in his 90's he is the original owner of the motor and boat,It looks like the " stop rod" where the throttle cable is attached was moved from it's original position as if to governed the speed "so it won't go that fast,Am i right to assume that there would be more carbon build up on a motor that has been pampered as opposed to a motor that has been run hard ? also would i see a major increase in speed? my first run with the boat was 23 mph, second run i moved the "stop rod " a little to gain more on my shifter "it was hitting the center console" and i got up to 28 mph thanks for all the help,i will let you know how it goes after the decarb.

 

[caldog101]

Re: 1984 115 hp compression ????

Well Guys,Did the decarb. the other day "LOTS OF SMOKE" Took it out in the bay, It ran great,only problem is it only got up to 28 mph at 4000 top rpm,I used an old tach from my 1991 evenrude 4 cylinder, this is a 6 cylinder,I was told after that i should have changed the dial on the back of the rpm guage,it was idling at about 1000 rpm according to the gauge,but then again not sure if that is right. i do know that i am not winding out at my top rpm. can anyone give me advice on the tack thanks

 

[caldog101]

Re: 1984 115 hp compression ????

Well,I think I am having carb problems,motor will only do 4000 rpm's. When motor is not running,and i squeeze the primer bulb gas pours out the middle carb,was wondering what this may be and what to do to remedy it thanks<br />p.s. i squited engine tuner through every orifice that i saw

 

[caldog101]

Re: 1984 115 hp compression ????

well it's been a while since my last post and would like to update everybody,rebuilt the 3 carbs, the middle carb float was full of gas so i think that was my problem,I was out yesterday and whats the term i am looking for "IT RAN LIKE A SCOALDED DOG!!!" Top speed was 38 mph it's a 20 foot boat and my top rpm was 5750,which comes to my next ? i am using a 13 1/4 X 17 prop and getting 5750 which i think is to high.I was thinking of putting a 13 1/4 x 19 prop and was wondering what you guys think,I am also impressed by the quick excelleration this motor has the first time i hit it full throttle almost got thrown out of the boat p.s. thanks to everybody that gave me help on this

 

[andy6374]

Re: 1984 115 hp compression ????

That is good WOT RPM for that engine, you wouldn't want to go any higher with the pitch as you'd start lugging the motor (not enough WOT RPMs). Sounds like things are coming together, glad to hear it!<br /><br />Good luck

 

[Clams Canino]

Re: 1984 115 hp compression ????

That's good WOT RPM, that doesn't mean to RUN it there all day. Ever try driving your car at WOT?<br /><br />Cruise it at 4200 all day and it'll love you. You might get away with a 19p stainless but that's it. You're good now - treat it nicely and it'll serve you well. <br /><br />-W