Convereting 115 hp Johnson to 135hp-NEW ???

[jaf65]

This also reply posted on previous 1974 115 conversion to 135 hp'
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Default Re: 1974 Johnson 115HP conversion to 135HP

This is a request for DHADLEY and/or IWOMBAT for a candid reply post to the following. Don't hold back -I respect your expertise!
In looking for a 90-140 hp motor for a 24ft. Pontoon I ran across (have not seen or heard it yet) that is reported to be a 1977 110hp Johnson (I think really a 115hp and a 1978 yr). The story is the owner (he taught shop tech) had his class under his super. take this motor and do a conversion by boring cyls. to .064 over, new Sierra Pistons, rings, bearings, seals and gaskets. rebuilt carbs off of a V6 Johnson with 1.75 bore. "Bell" Exhaust and one new coil. No mention as to new or replacement heads. This man died before it was even run and his friend got it from wife and then sold it to the man who is now trying to sell it. This conversion was 6 yrs. ago and it has been upright on a rack inside since. Was started by seller in 1999 foe 2 minutes and reportedly ran strong and peed water. Reportedly T/T had worked when purchased by seller but now does not operate but makes a sound. Pics show a bubble looking back and a metal front where the 4 carb . throats are visible (no cover over front). The carb throats are two on top and two lower each set of two horizontal to each other. Neither seller nor myself are particularly adept at this level of marine mechanics. So, the questions dor yhour comment are:
1. Does this sound like a proper conversion
2. If purchased would you expect additional work/parts needed?
3. for general use on pontoon boat is this a good motor?
4. If I go to inspect motor for possible purchase, what tests/visible condition should I look for?
5. Should there be some sort of cover in front of the metal part where the carb throats appear.
6. should there be one or more power packs on motor or can electrical be converted so as to not use coils
7. Would you recommend this to a basically non-mechanic?
8. Does the resale or part-out value of motor worth the sale price of
$700.00
9. If better to discuss over phone reply here and I will give my number.

Sorry this is so long but am at a confused decision point

 

[Faztbullet]

Re: Convereting 115 hp Johnson to 135hp-NEW ???

Several issues noted as 1) Sierra does not make a .064 piston only Wiseco (2) No difference between V-4 & V-6 carbs except throat size and I dont know of a 1 3/4 carb made. The "bubble exhaust" if it was just added (bolted on) without the deflectors and exhaust web in block cut it wont add much hp(maybe 5HP) as boring to max oversize also did not add any noticable hp to engine.
1. Does this sound like a proper conversion...............maybe
2. If purchased would you expect additional work/parts needed?........yes carbs/impeller
3. for general use on pontoon boat is this a good motor?............yes but it will like gas
4. If I go to inspect motor for possible purchase, what tests/visible condition should I look for?...compression,spark,condition of lube in lower unit,why trim doent work,if high speed jets were increased due to boring.
5. Should there be some sort of cover in front of the metal part where the carb throats appear..........yes
6. should there be one or more power packs on motor or can electrical be converted so as to not use coils... 1977 will have single pack and 1978 will have 2 packs, you got to have coils
7. Would you recommend this to a basically non-mechanic?...........on if he has a mechanical minded friend that works for "cold ones"
8. Does the resale or part-out value of motor worth the sale price of
$700.00............................if it checks out its worth that but not much more.

 

[iwombat]

Re: Convereting 115 hp Johnson to 135hp-NEW ???

Honestly, if buying new, I'd be looking for a 80s model 115hp crossflow, or better yet a later model looper. The latter will be more spendy, but easier on fuel and have better hole shot. (assuming a 115 is big enough to push your rig.)

Replacement parts are just that much easier to come by on the '78 and later crossflow models. So, unless you get a screaming deal on a GOOD RUNNING '75-'77. Keep looking for a later model.

 

[jaf65]

Re: Convereting 115 hp Johnson to 135hp-NEW ???

THANKS-THANKS & THANKS to IWOMBAT and FATZBULLET- You guys are great and have saved me some valuable $$$$$ and a whole lot of most likely misery both to myself and from my wonderful wife!! I have just found IBOATS and this is the best source site for so many marine ????? and thank you again for your willingness to take your time to help us mentally challenged in these areas.

Now, another question- notwithstanding IWOMBAT's comment on the 80s Loopers, what are your thoughts on a late 1980s 115 hp Inline 6 ($1500) in good running, fresh water condition? I've read a littlle about gas guzzling and piston burning but am more concerned about not being able to run the motor (on the pontoon boat) in the recommended rpm range. Am really leaning toward IWOMBAT's recommendation of the 80s 115 cross or looper.

 

[iwombat]

Re: Convereting 115 hp Johnson to 135hp-NEW ???

I think you already answered your own question. Hold out for what your gut says is the right purchase.

 

[Faztbullet]

Re: Convereting 115 hp Johnson to 135hp-NEW ???

It really doesnt matter what brand engine you purchase, they all need to run in their recommended rpm range. The I-6 Mercury is a great motor with plenty of low in torque and pretty decent fuel usage. I myself would try to find a mid 90's 115 60? as more compact and get power to weigh ratio and good on fuel.