Calling all 170 owners with a 70/100 hp motor....

[alandry100]

I have a 70 2 stroke on my 170. I top out at around 28 (30 down wind) mph with two adults two kids a dog and full fuel, with 5 adults around 26mph at 5200 RPM. Fast enough for me and not bad out of the hole - would be great with tabs. Cruise at 24 at 4400. Can run all day on 15 gallons. Don't have precise burn numbers.  I'm definitely not looking for a new engine.

[Fletch170]

I would sell both motors, and buy something like this:

http://www.ebay.com/itm/Used-1990-Yamah ... fd&vxp=mtr

As mentioned, the parts to fix the 70 may be cost prohibitive. Just a thought.........

[aquasportbeezy]

i have a 115 mercury on mines and im not satisfied i want a 150 lol

[pzart]

I have a 1989 Evinrude 110 that weighs about 320 lbs, tops out around 43 mph with a 13x17 prop with more power than I need, 2 men with beer and gear. I could easily go to a 13x 19 for more speed. The front gets slightly bouncy above 40 mph on smooth water so I put 3 bags of softner salt in the nose, ride perfect now and brought my scuppers above water level. In one way it's like having the little woman sitting up there.....but no bitchin I would like to try a 13x19 but havne't been able to find one cheap yet.

[Coverhill]

Here is some info that may be of help on the subject of what HP for a 17 foot Aquasport.

I have a 1988 17' Aquasport that I've owned since "new". Originally the boat came with a
90hp Yamaha carbureted engine, which was very reliable but which gave me only about
3.5 statute miles per gallon at 3400 RPM and a speed of roughly 22 statute miles per hour.
I know that these figures are accurate because I kept a record of this info.

In January 2012, I repowered my boat, mainly because the new fuel injected motors are
SO MUCH more fuel efficient. My main goal was to obtain maximum fuel efficiency.
After looking at all the manufacturers and technologies I decided to go with 2-stroke fuel
injected technology, rather than 4-stroke technology. Dusky Sport Center in Hallandale,
Florida gave me an excellent price on a 90hp Evenrude "E-tec" engine (model E90DSL)
and did the engine change out. I got $1,500 for my old Yamaha and its controls, which
they help me sell to someone who buys motors. Dusky did an excellent job rigging the
new motor to my boat, which included Evinrude's digital "I-Command" multifunction
gage that shows (1) GPS speed, (2) Gallons per hour fuel burn to the tenth of a gallon,
(3) Miles per gallon, (4) RPMs, (5) Engine temp, (6) Battery voltage, etc.

I also considered going down to a 70hp E-tec, which in my opinion is adequate power
for my 17' Aquasport. Ultimately I chose the 90hp E-tec since it is built on the same
block as the 70hp and the weight of both engines is about the same.

Because my highest priority is fuel efficiency I specified that when "propping" the
engine that I wanted to turn less than 5000 RPM at Wide Open Throttle. My new engine
turns up 4860 RPM at WOT. fully loaded for fishing. I cruise it now at 3100 RPM which
gives me a solid 20 statute miles per hour and 6.5 statute miles per gallon of gas.
That's a good 80% better fuel efficiency than the old 90hp Yamaha. My new top
speed is 38 statute miles per hour, faster than water conditions will allow 90% of
the time.

Below is a photo of the new "Performance Specs" card that I made up last month
on this new combination. All those RPM/GPS SPEEDS were done in slack water that
had only a light chop. The card also shows the boat weight during these tests as
well as the exact prop thats on my new motor.

Hope this will be of help to others.

Coverhill
North Palm Beach, FL

[Georgie]

Coverhill...EXCELLENT post!    

Valuable and detailed information for the OP to consider.  My one and only question has to do with the RPM's.  I know nothing about the new E-tec's, but I do know that most engines are designed with an optimal RPM range and intentionally reducing that range by increasing prop pitch puts added strain on the drive train that it's not necessarily engineered to handle over long periods of time.  That said, I did just advise another poster the other day that prop changes can conceivably help cruising fuel economy as long as top end RPM's aren't reduced excessively.  What is factory recommended top end for the E-tec you bought?

[Coverhill]

Ryan,

Evinrude specifies in writing that the "Full Throttle RPM Range" (their language) for
both my 90hp E-tec (as well as for the 75hp E-tec, which is built on the same block)
as "4500 - 5500 RPM".

As you can see this isn't a tight range span and allows for quite a bit of flexibility in
"propping" a specific installation. Within the stated RPM range one might choose to
prop for quick acceleration (hole shot), top end speed, etc.  I have chosen to prop
for fuel economy at a modest cruise speed. I did the "speed thing" decades ago,
competitively raced boats back then, but now my Aquasport is about exploring and
tarpon fishing and just enjoying being on the water in a well designed, well crafted
boat.

I do know from years experience that when selecting a prop this theory is applicable.
The lighter the boat the higher the prop pitch; the heavier the boat the lower the prop
pitch. Work boats should have lower pitched props than runabout boats. For a quick
"hole shot" use lower pitch; for max top end speed use more pitch. To get the
"perfect" prop for a specific installation takes lots of experimentation, both in the
style of the blade as well as the pitch of the blade. Prop diameter is much less
flexible since it's limited to what will swing without contacting the motor's lower unit.
Most current manufacture outboards seem to have about a 1,000 RPM spread for
their recommended "Full Throttle RPM Range", although a few may have about half
that amount.

P.S. - I don't want to leave without thanking you for telling me how to easily move photos
from my "Photo Gallery" to a post in these forums. Your "control C" and "control V", and
the explanation of what they did were the magic words I needed. Good Show !

[powersportcomposites]

Ok update here guys. I have started to rebuild the 70 because its not going to do anyone any good in its current state. Hoping to just replace one piston, but the other two feel pretty darn loose in the cylinders. I may just replace all three pistons
As for prop pitch , its currently a 13/18. Jetting I haven't looked at yet. I would be happy to cruise at 25-30 ish if the 70 can swing it, would much rather have efficiency than speed.
It does baffle me a bit though that the 100 is so dang thirsty. I would love to get the darn thing  dialed in a bit more...but I feel like its not going to change too much. Here is what I really don't understand....in theory, 1 gph for every 10hp  at WOT....right. I currently have a top speed of 38mph....so at a theoretical 10gph at 38mph that's 3.8mpg. So how is it that I manage to average 2-2.7 mpg on a trip where I spend less that half of the running time at WOT?

[powersportcomposites]

Also I would like to thank all thread contributors for the helpful and detailed responses I certainly appreciate you all taking the time to reply.

[gran398]

Derail:

All of you guys are relatively new, and you've brought excellent input to the merry band.

Thanks for joining, great job

[Georgie]

PSC -  How far have you gone tearing apart the 70?  Before you go replacing pistons just because they seem loose, see what you have in each cylinder (your original compression readings would not really indicate "loose" pistons).  The pistons may or may not be scored (i.e. might be perfectly reusable, you could have stuck vs blown rings, and if you blew rings in the middle cylinder, depending on the depth of the gouges in the cylinder wall, you may be able to overbore or may need to replace the sleeve entirely.  measure the piston/cylinder clearance to see how close it is to factory spec (there is a very specific tolerance here).  I don't have a manual for the 3 cyl OMC's but I know my V-4 manuals has the correct clearance range in the specs pages.  Also, if you're going so far as to rebuild this one, at the very least you should use all new piston rings and spend the $$ to have the shop hone the cylinders true and get the block and cylinder head squared again so the surfaces mate properly when you replace the head gasket and put her all back together.  Always spend the extra money on all new soft parts too (Gaskets and O-rings).  They don't cost a ton, but certainly help you avoid premature failure due to cracking or other wear.

RE: the Javelin, I don't really know why your numbers are so low.  I have to imagine it's just poor/inefficient mixture.  What do your plugs show? any fouling?  Any unburned fuel/oil dripping from underneath the propeller hub?  Something is definitely off though, so work with us and maybe we can get her dialed in before you swap to the 70 so you can either store or sell her as a properly running engine.  See if you can read the exact prop size in the face of the prop hub.  Also, finding out what size jets you have will help too.  The more pics the better.

[powersportcomposites]

The jets are 34's. Inside the carbs....clean as a whistle. Surprisingly so actually...
Pics as requested....


I just recently gave her a lick of of paint

[Georgie]

Ok, now we're getting somewhere.  8)  The carbs look pretty good, and those 34 jets are probably stock but you need to check the high and low speed jets (aka orifice plugs) in the carburetor bowl to be sure.  Look at part numbers 3 and 23 in the linked schematic.  I believe you posted the size for the jets labeled as part No. 7?

http://www.boats.net/parts/search/BRP/JOHNSON/1980/J100TRXCSC/CARBURETOR/parts.html

Couple more things while you're at it.  I don't know what you're using for cleaner/solvent, but I use B12 chemtool since it does a great job cleaning and comes with a narrow straw and LOTS of aerosol pressure so it works real well to blow out any gunk from every single port, venturi, jet and feeder tube in the carbs.  WEAR GLASSES AND GLOVES!!!!!!!! Try to also send some photos of the electrodes from all 4 spark plugs, and make sure to remember which plug comes from which cylinder (important to not confuse cylinders during diagnostics).

oh, and by the way....like the boat!!  nice and clean and very original from what I can see!  

[powersportcomposites]

Thanks I've worked hard on it.
As requested...
#3 is a "28"
#23 is a "54c"

[powersportcomposites]

Where did everybody go? I thought we were gonna get to the bottom of this!