Main Jets-115 Johnson

[walleyehed]

I have a 115 Johnson that I recently O/H'd, and when I got to the carbs, it had 68C main jets. This engine came from Florida with #4 stuck....I found the pistons to be wisco's-20 over and the bore was only .018 over standard. Anyway, I opened the bore on all 4 to .021 over standard and installed new Wiscos. I also installed a set of Boyesen reeds.<br /> I'm very unhappy with the performance of this engine, as It replaced a 1977, 115hp Johnson-which hp was rated at crank-and the "newer" 97 model gives the same performance with the same props.<br /> A big factor to all of this is I operate this engine at 3600ft above sealevel.<br /> Can anyone tell me what jets came standard, and how far can I go with the timing-this is not the OIS ignition.<br />Eng. Mod#J115TSLEUA, SER# G 04217749.<br />It's a 90deg., crossflow.<br />Thanks for any help!

 

[Dhadley]

Re: Main Jets-115 Johnson

68C is correct. What is the wot timing set at?<br /><br />Good luck!

 

[walleyehed]

Re: Main Jets-115 Johnson

Timing is set at 29deg. max advance

 

[walleyehed]

Re: Main Jets-115 Johnson

I also forgot to mention, I have been doing the W.O.T.kill check on plug color, and after about 20hrs on the eng., I went to 67C jets, and have determined I'm still slightly on the rich side, but noticed no increase in RPM with Jet change....am I over-looking something else?????

 

[Dhadley]

Re: Main Jets-115 Johnson

Thats really pushing it. Be very careful. Max recommended is 28, after break in. I definately would not go to leaner jets. Remember when you do the "kill motor - inspect plugs" thing that this is a two stroke, not a four stroke.<br /><br />What is the top rpm and how does that compare to the older motor's rpm? I wouldnt expect a great deal of difference - especially if the top rpm is 5500 or so. remember - you have the same bore, same stroke and same gear ratio on the two motors.<br /><br />Good luck!

 

[walleyehed]

Re: Main Jets-115 Johnson

My boat is a Starcraft 1800 fisherman (alum).<br />The 1977, 115Johnson was rated at the crankshaft, which has been calculated to 92hp, propshaft hp. I'm at 3600ft. and the loss of power is 3%per1000ft-10.8% powerloss, which puts me at about 82 actual hp. With anything newer than '85, they were for the most part, rated at the propshaft, which the output at my alltitude would be approx. 102hp of my 1997 115. So why is 20 years technology and 20 more hp not turning the same prop more RPM.<br /> Another question I have is if the bore and stroke are the same, which means nothing until you add carbs, why does the newer engine use .011 bigger jets (from the factory) if all else is the same??????

 

[Dhadley]

Re: Main Jets-115 Johnson

Carbs can, and do, have dramatically different size jets according to other calibrations and the way they are built even though they appear the same. <br /><br />Without knowing you rpm its difficult to make assumptions. If you are in the low 5000 range both motors may be making very close to the same power. Once you get into the upper range then you may see some difference.<br /><br />Good luck!

 

[walleyehed]

Re: Main Jets-115 Johnson

Thanks for your thoughts and advice! I think I'm going to set the timing back to 28 and maybe even put the sealevel jets back in....Bad part is, I bought 4 or 5 different props that I thought would work on this and I've got a couple of SS props to unload if someones' lookin'.<br />Thanks again,

 

[G DANE]

Re: Main Jets-115 Johnson

walleyehed please e-mail me salg@romantiskbad.dk

 

[ledgefinder]

Re: Main Jets-115 Johnson

What rpm are you maxing out at?<br /><br />The '97 115 is a 'bubble-back' motor, more like the '77 140, than your '77 115. The '97 115's power will be up higher in the rpm range than your older 115's was, and the '97s powerband may not be as fat. <br /><br />Prop is so you let the '97 spin at least 6000 rpm with just you in the boat...then decide how it pulls compared to the '77. I'd borrow and try a 15" pitch prop (if you haven't already)particularly at your altitude.

 

[walleyehed]

Re: Main Jets-115 Johnson

I've ran this several more times since the original post, and with my timing at 29deg., and 67C jets, 13-3/4X15 prop, eng. raised to second hole, stingray on the cav. plate-WOT with trim for max performance, I get 5600rpm and about 36 MPH.

 

[bassnmamma]

Re: Main Jets-115 Johnson

Now I know why you are being so helpful, having just gone through the same set up headaches yourself that I am currently having! So you tried advancing the timing too? I have got to get my boat all set up by August 3 as I'm going to Flaming Gorge with church youth group and I am the official smallmouth fishing guide! Gulp. So much to do, so little time.

 

[walleyehed]

Re: Main Jets-115 Johnson

Ledgefinder, If I put a prop that will go to 6000, I will be laughed at terribly by the good ole' boys, cause that would be a 13" pitch, commonly known as a pontoon prop. I've got a friend here with a simular starcraft, 17'6"...mine is 18', he has a 110 jonny and runs an 11" pitch on it just for the slower troll and it will just get on plane at 5900-6000, and 17MPH. a 13" will add just a tad of speed but still go to 6000, but stay on plane at 5600-I don't want to run more than a few seconds over 5600-5700.....mine is 4500-5500 max, but I too, like to set them up for 6000.<br />We've always had great success with the 13.25X17" props on the 115's on 17'6" boats, and I think mine is heavy enough, I may not get what I want with the 17". This may sound strange but My best overall performance prop with 2 people is my 13.5X18" RAKER. Top rpm is around 5350, but this prop holds better at higher trim and I get about 43 MPH with it. The hub is vented, so I get a good hole shot too, I just wish I could find the 5500 mark with a good SS 17", and 2 people in the boat. Maybe if I lifted the engine, it would fall off and I could just put a new 150 on it..........