85 to 115 Johnson

(model 85esl75e serial j4308395t) 15' V hull Gasstream bassboat,

Just added bubble back exhaust plate off a 140hp got 200-300 extra rpm from this alone, 5" set back jack plate set at 3" below pad, 4 blade 18p prop, added tell tale and h2o gauge + new tach, hot foot with all new cables.

Can't wait to try it all on the water.

Last upgrade, I am putting on 115 hp carbs and Boydsen reeds this weekend. Two techs at different companies have told me that I do not need to change the jets as the 115 carbs should ritchen it up enough.

Any thoughts.

Re: 85 to 115 Johnson

The 1975 85HP engine is a totally different block from the 1975 115 and 135, so it is hard to guess what the result would be. Displacement, stroke, bore etc are all smaller. Whatever carburetors you use, you should probably try the using the jets that came with the carburetors first.

Re: 85 to 115 Johnson

The 115 is a bigger bore and has bigger ports than the early 85's so the 115 carbs should be plenty rich as is on the 85 for sure.

Re: 85 to 115 Johnson

ezeke's comment parallels my experience. Depending on the 115 carbs you use, you may wind up spending time rejetting. Some early 115 carbs were not the large 1 5/16 throats, some later ones are...The original high speed jets in my 92 cubic inch 1972 85 were .057. I put a set of early 1 5/16 125 carbs on it and it would not run. The high speed jets in the 125 carbs were .072 jets. They flowed too much fuel. I finally went back to the original 85 jets, and then went up from there. I settled on .062 as I recall. Despite all the fiddling, the larger carbs worked great and it was worth the time. Picked up about 300 rpm. I can't speak to any change in the idle jets, as my 125 carbs had adjustable idle jets.

Re: 85 to 115 Johnson

So glad to hear good news. I was sure it would help. I think the jack plate and the 4 blade prop will help a lot. Thanks for the jet guide.