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

[powersportcomposites]

Ok guys....I'm looking to replace the 1980 Johnson Javelin 100 I'm currently running on my Osprey 170. At the moment I average 2.3 mpg and its killing me. Top speed cooler and livewell full with two passengers (including myself) is 38 mph.

If I swap to a 1992 Johnson 70 horse 3 cylinder, what top speed can I expect and what kind of fuel consumption? Also what cruising speed?  
Thanks so much

[flounderpounder225]

Just an educated guess, probably 30 mph top speed, maybe a tad less, fuel efficiency will go up considerably, the inline 3 was a great motor, at cruising speeds I could see your mileage double.  The jav is a v4, they were also great motors

[Blue Agave]

IMO you will not see any fuel savings. Although the 70 hp is a newer and more fuel efficient motor, you will have to run the motor at a higher RPM to maintain the same cruise speed.

[Fletch170]

I'd agree with Blue, the 70 just isn't enough for the boat.

[Fletch170]

Honestly, I did a lot of research when hunting for power for my 170. I ended up with a 115 yamaha, but I really feel the perfect power for that boat is a 3 Cyl Yamaha 90. Bulletproof gas sippers.

[Georgie]

IMO - the boat should still move fine (depending on your definition of "fine"   ) with the 70.  Had an '88 'Rude 70 on my father's 17 whaler montauk  that moved the boat at a real nice clip (guessing 35-ish), but not sure about consumption on those 3cyl engines.  Would have to compare some consumption charts to get a realistic idea.   I'm a bit confused as to why your V4 100 is sucking so much fuel, though, as I have a V-4 135 on my 18 wellcraft and I think I get better consumption than that.  Is it original/stock?  Have you considered downsizing the carbs/ jets to reduce consumption if that's your main priority?  Would cost quite a bit less than buying a new motor, but not sure how much you'd gain in the economy end of things.

This iboats discussion may help:http://forums.iboats.com/non-repair-outboard-discussions/fuel-consumption-late-80s-60hp-3cyl-vs-90hp-4cyl-15321.html

I also feel I'd be remiss if I didnt ask how she performs with the 100.  Hole shot?  38 mph sounds a tiny bit slow. unless your boat is waterlogged or otherwise loaded down.  Certain you have the best prop for your rig?  Do you have a tachometer, b/c max RPM should land at about 5500 for that engine if it's propped correctly.

Let us know a few more details!

Also,  I think fletch is dead-on with the Yammi 90.  

[powersportcomposites]

I will check the prop pitch and get a accurate digital tach to check rpms.

[powersportcomposites]

The holeshot right now is great, and it is plenty fast for my needs, but spending $70 on fuel for a 34 mile round trip is just crazy to me

[jdupree]

I can't add any fuel burn numbers, but I did have a 1986 170 with a early 90's Johnson.  I guess it might have been the crossflow??  If I recall, she was great on gas.

I found the 90HP to be the perfect setup for mine.  Hole shot was great and so was top end.  If I remember correctly my top end was around 42mph.  I know that the size prop needs to be figured into the equasion, but just giving you my experience with my 170.

[Fletch170]

As mentioned, I got the 115 for a song, so that's what I went with. I removed all the water logged foam, and used 4LB foam in the stringers. She should be back to factory weight (around). From what I've heard, light on fuel and trimmed up with one guy, I'm looking at upper 40's. Full of fuel and beer, she'll likely see 40.

I believe they are rated to a 130 HP, which seems insane to me. unless you are pulling a skier, the 90 seems like the way to go.

[powersportcomposites]

Kicker is I already have the 92' Johnson 70 hp.
It just has low compression in middle cylinder. Debating on spending the couple hundred bucks in parts to drop a piston in it and give her a try.

[Georgie]

The holeshot right now is great, and it is plenty fast for my needs, but spending $70 on fuel for a 34 mile round trip is just crazy to me

If that's the case, then there's a very good chance you can rob from your hole shot to improve cruising efficiency by slightly increasing prop pitch.  I'm by no means a guru in this art/science and you'd definitely want to educate yourself first, but in concept it's honestly no different than shifting to a higher gear on your bicycle.  The key is making sure you don't decrease your top end RPM below the 5400-5500 range by overloading the engine. Some shops will allow you to try out test props until you can dial in on the right match for you engine/boat/water type combo.

Also, double check the carbs and jets as I mentioned earlier.  Unless you bought your boat all new, a prior owner may have tweaked the mixture for various reasons.  you can likely just swap out some jets for those that come stock in the 90HP and you'll save some fuel that way.  Farley will probably have some input on this one.  Do you have a model number for your Javelin so I can research specs?

[Georgie]

It just has low compression in middle cylinder.

Define "low"?...as compared to the other two cylinders which are what??

[powersportcomposites]

Low as in 110/60/110.   Pulled the head. Cylinder is scored. Definitely needs a piston. I would much prefer to just get decent mileage out of the javelin and I'm willing to play with jets and pitch with a little guidance. This is far from my area of expertise.  Thanks for the help, ill post serial number tomorrow

[Georgie]

Hmmmm...How deep are the gouges in the cylinder?  Did you take any photos?  I imagine at 60 PSI the block probably needs to be resleeved in that middle cylinder before rebuilding which is another chunk of $$.  This question of yours has become a bit of a conundrum.  If you already own both engines, and economy is your priority, then perhaps rebuilding the 70 is a better long term option, but since the 70 has already had a serious failure it would have to be done carefully or you're just throwing away $$ and labor.  And would you be paying for the rebuild or doing it yourself?  

Another almost random question, but are you paying extra for ethanol free fuel?  If so, stop.  It's not necessary for these old crossflows.  Just make sure you have good filtration, resistant hoses, and treat your fuel if it's gonna sit for extended periods.  Factory manual even says these engines are fine up to 10% ethanol.

Lastly, regarding the jets, look at the linked schematic below and find out what you have for jets (aka orifice plugs) indicated as part # 3, 7, and 23.  You will probably need to customize an existing screwdriver you already have (using a bench grinder) so it fits into the holes without binding on the threads.  You also MUST make sure the screwdriver you use has a larger diameter handle for torque, and a very sharp/square tip for optimal "bite" on the jets.  If you strip a jet you either are stuck with what you have or pretty much have to buy a new carb.   You may even want to squirt some PB Blaster or similar penetrant lube into the ports before trying to remove the jets if they've never been touched.  The jet numbers are stamped in the brass either on the top of the head of the jet, or on the side.  They can be hard to read so I hope you have good eyes. :| ...and keep a safe bin or ziploc handy so they don't get lost.

On a personal note, I don't know your finances or priorities, but as a hands on boat owner I'd be more inclined to tweak a properly running engine regardless of age than try and rebuild AND tweak a busted one...  2 cents.

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