Classic AquaSport
General Aquasport Forums => Aquasport Discussion => Topic started by: powersportcomposites on April 05, 2013, 12:37:52 AM
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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
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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
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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.
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I'd agree with Blue, the 70 just isn't enough for the boat.
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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.
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IMO - the boat should still move fine (depending on your definition of "fine" :lol: ) 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. :D
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I will check the prop pitch and get a accurate digital tach to check rpms.
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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
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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.
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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.
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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.
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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?
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It just has low compression in middle cylinder.
Define "low"?...as compared to the other two cylinders which are what??
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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
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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. :shock: 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
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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.
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I would sell both motors, and buy something like this:
http://www.ebay.com/itm/Used-1990-Yamah ... fd&vxp=mtr (http://www.ebay.com/itm/Used-1990-Yamaha-90ETLD-90HP-2-Stroke-Outboard-Boat-Motor-20-Shaft-/400455194621?pt=Boat_Parts_Accessories_Gear&hash=item5d3cfd57fd&vxp=mtr)
As mentioned, the parts to fix the 70 may be cost prohibitive. Just a thought.........
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i have a 115 mercury on mines and im not satisfied i want a 150 lol
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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 :mrgreen: I would like to try a 13x19 but havne't been able to find one cheap yet.
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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
(http://www.classicaquasport.com/gallery/data//500/Fuel_and_Performance_Specs_Card.JPG) (http://www.classicaquasport.com/gallery/showphoto.php?photo=7066&title=fuel-and-performance-specs-card&cat=500)
(http://www.classicaquasport.com/gallery/data//500/1988_17ft_Aquasport_Capacity_Plate.jpg) (http://www.classicaquasport.com/gallery/showphoto.php?photo=7069&title=1988-17ft-aquasport-center-console-osprey&cat=500)
(http://www.classicaquasport.com/gallery/data//500/17ft_Aquasport_with_65qt_Yeti_Cooler_Seat_Original_Aquasport_Seat_Frame.jpg) (http://www.classicaquasport.com/gallery/showphoto.php?photo=7033&title=aquasport-helmsman-seat&cat=500)
(http://www.classicaquasport.com/gallery/data//500/17ft_Aquasport_with_Bow_Mount_Trolling_Motor.JPG) (http://www.classicaquasport.com/gallery/showphoto.php?photo=7072&title=17ft-aquasport-with-bow-mount-trolling-motor&cat=500)
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Coverhill...EXCELLENT post! :thumright:
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?
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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 !
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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?
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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.
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Derail:
All of you guys are relatively new, and you've brought excellent input to the merry band.
Thanks for joining, great job :thumright:
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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.
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The jets are 34's. Inside the carbs....clean as a whistle. Surprisingly so actually...
Pics as requested.... (http://i293.photobucket.com/albums/mm79/nickireson/IMAG0316_zps7d3a2145.jpg) (http://i293.photobucket.com/albums/mm79/nickireson/IMAG0447_zps19291e8e.jpg)
I just recently gave her a lick of of paint
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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! :thumright:
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Thanks I've worked hard on it.
As requested...
#3 is a "28"
#23 is a "54c"
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Where did everybody go? I thought we were gonna get to the bottom of this!
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PSC -
Still with ya. Have been in the field for work all week. No computer time.
I'm a bit scattered trying to provide info for both the 70 and the 100 in one thread. Perhaps dedicate this thread to the 70 HP since it's in the thread title, and start another for tuning the 100? I imagine you'll get more poignant and specific responses. Your jets do appear to be factory original. Need description/photos of spark plugs for each cylinder still. Also, have you been able to speak to any local shops about testing propellers? I'm curious what a slightly steeper pitch prop might do for your ride. The more info you provide, the more people will respond, and while a pain to provide, pics really do encourage others to reply.
Your javelin, does it have the stock "bubbleback" exhaust between the cylinder heads?
Your carbs, what size throat is stamped in the forward face of the aluminum?
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Hey Guys,
I've been watching Georgie maneuver through the details on this with some outstanding information. I just want to make a couple of points. First, all 2 stroke engines have loose pistons when cold. The tightest clearance is in the skirt area below the wrist pin. The skirt is what keeps the piston running square and parallel to the bore. Thats why you will usually see minor scoring show up on the bottom of the piston first. When the engine warms up, the piston will expand to a running clearance of .001-.0015 and the oil film is what keeps the bore and skirt happily almost rubbing against one another and protects the two from coming in physical contact. the upper part of the piston has more clearance and the rings support the piston and are allowed to breathe back and forth (in and out) for compression and exhaust strokes. This breathing is what keeps the ring lands on the piston clean and not jamb with carbon from combustion. Again, the only thing preventing physical contact is a very thin film of oil. OMC called the rings "pressure back" because of their design and the self-cleaning action. As for our V4 fuel economy, I would definately check full advance timing and see if its anywhere near where it is supposed to be. Then go through a meticulous throttle and timing syncronization process exactly per a factory manual. When we did Scotty's 75's on Miss Delmarva, the engines were so far out of time and throttle sync that I cannot understand how they even ran. Some people feel compelled to just start turning screws without any knowledge of what they're doing. My $1.385
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I suppose I should have said this in my last post. I have decided the 70 isnt ever going on the 17. I may fix it and sell it but for our current purposes, disregard the 70 entirely. In light of this would it be appropriate to start yet another thread? I just didnt want to ticdk anyone off by cluttering up the forum. And once again thanks so much for all input so far. Georgie I will provide the info requested in a few hours
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How bout you change the section of title of this thread from "70hp" to "100hp".
That way, you can continue the thread.
Work for you?
Thanks.
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Can I do that? I dont see an edit option
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PSC-
Saw your fuel tank thread and it reminded me to get back to helping dial in your Javelin. Carbs do not appear to be your immediate problem, so we'll need a few answers to some additional questions to keep going.
1) How do your spark plug electrodes and insulators look? Black and sooty or oily? brown/coffee colored? white and ashy? can you send photos, and do all 4 plugs look the same, or is there variation top to bottom or side to side?
2) Do you have a timing light and/or know how to test timing? Fitz has a VERY good point that the timing could be off. If it's retarded or advanced you'll get sub-optimal combustion which means less power to push the boat, poor fuel efficiency, and can even damage the engine in a relatively short amount of time.
3) Still would like info on the RPM's when at WOT, especially the numbers you see using the two different props. RPM's at idle would also be helpful.
4) What's the carb mouth measurement (stamped on the face of the carb)?
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The plugs were VERY brown and oily. Looks super rich to me. I'll post pics tonight. They were all equally brown and oily. I do in fact have a timing light.