jonnyrude 88 and 90hp repower ?'s

[bryanwess2000]

I have a 1982 16' sylvan sportster that i mounted a 1977 merc 850 on
I'm fairly happy with the combo but would like a newer engine after I
restore the boat. The mec 850 has compression as follows 1-130psi, 2-120,
3-138, and 4-140. there is good 1/2'' spark on all plug wires. the motor
has ran great for 4-5 years other than an original starter going out(to be expected) and needing a new wireing harness(which I made, couldn't justify
paying $400-500 dollars for a new one). Also replaced the rotten wireing
on the motor. So just about all of this motors known weaknesses have been
addressed. However I find myself wanting a newer, stronger motor, particularly a 1985-newer johnson/evinrude 88spl or 90hp with tnt which I don't currently have. My boat has a hp rating of 85hp but there aren't any newer motors I like that are rated 85hp.

My question is would a 88hp or 90hp jonnyrude be safe on my boat or would
it be unsafe. My boat is basically the same as a starcraft supersport, or equivalent smokercraft( aluminum deep-v bowrider). The transom has been
replaced by me 3 months ago.

I've read that the 1985-newer jonnyrude 90hp actually put out around 100hp
at the prop, can anyone confirm or deny this ,maybe someone dynod one before. Thanks.

 

[JB]

Re: jonnyrude 88 and 90hp repower ?'s

If it is rated for 85HP max, put 85 or less on it. That boat should perform satisfactorily with anything over about 60HP.

You can only be a little bit overpowered if you can be a little bit dead.

Ignore those myths about certain engines putting out way more or way less than the spec. They aren't true.

 

[Lion hunter]

Re: jonnyrude 88 and 90hp repower ?'s

I'd stick with the rating. And, I'd also run that Merc till it died. I really doubt that your going to notice any increase at all. It may show up on a GPS but the seat of your pants driving will be about the same I bet. Sounds like you've got that Merc where you want it why take on another problem? I run a 60hp on my 16' Aluminum Crestliner. It's rated for 90 but I am more that happy with a 60. The old Johnson has a hole shot you can't beleive but that's where it ends, 0-30 in nothing flat and no faster. Good enough for me.

 

[tashasdaddy]

Re: jonnyrude 88 and 90hp repower ?'s

i would do a decarb on the Merc and run it till it dies, and i do not like Mercs. i agree, it is hard to be the 88 and 90. but i would be looking for a 70hp 3 cylinder Johnnyrude, get the controls with it, as the merc and J/E controls are not compatible.

 

[bryanwess2000]

Re: jonnyrude 88 and 90hp repower ?'s

I decarb it usually 2x a year. The compression numbers have been about the same since I bought it. I pulled the exhaust cover last night to replace the gaskets and noticed the top 3 pistons have some scratches on them. The top 2 cylinders piston rings have a couple deep scratches on them. I'm guessing thats why the top 2 cylinders are reading lower on the compression test. Hopefully it'll last a couple more years, It's ran with these compression numbers for 4-5 years and about 100-150 hours total.

 

[tashasdaddy]

Re: jonnyrude 88 and 90hp repower ?'s

run it till it croaks, start putting $10.00 a week, in a box, to use to replace it. it won't hurt as bad, when the time comes.

 

[dwco5051]

Re: jonnyrude 88 and 90hp repower ?'s

Gotta agree with tashasdaddy. My favorite fishing boat had a '76 850 on it and just went south a year ago. The hobbs meter had about 2700 hours on it when it quit working about 5 years before the motor died. If I had put 10 bucks a week in the cigar box I would have had about $23,000 stashed away.

My top cylinder showed scoring and about 5 psi lower compression for the last 5 years of its life. These motors are known for running the top cylinders lean so pay attention to your fuel filter screen and pump diaphragm. The O-ring on the fuel pump cover is known for drying out over the winter. I have seen two different motors like this with cracked covers where the screw has been over tightened to stop leakage. Replace the ring every year and carry a spare. Cheap insurance.

Some day when the top one or two cylinders only show 10 psi you will know it finally died from in-line merc syndrome.

Stay with the capacity plate rating and stay legal. A few horsepower extra is not that noticible. I once fished with a guy who had a 175 that he had put 150 decals on and could not tell any difference than my buddies identical boat with a 150.

BTW, when mine finally quit I ran into a twenty year newer 20' bass boat with a 175 for about twice what just the parts would cost for a rebuild. Sold the old rig for $500 so I am still $22,500 ahead

 

[bryanwess2000]

Re: jonnyrude 88 and 90hp repower ?'s

I guess it's staying on the boat till it dies. I can't complain too much It's
lasted 5 years with only minor problems and survived a few overheats from
me not seating the water pump base right and quite a few lean runs from a leaking fuel line. I recently did a link and sync on it and was hoping to gain some power from it but the timing was at 30* and I backed off to about 21*
as instructed and lost some power and around 2mph on top end. It should last
longer now, I'm surprised it didn't burn a hole in the piston with so much timing and running lean on top of it, but I ran it like this for over 4 years and who knows before I got it.