1989 Evinrude 70 HP / Running Vibrations / Fuel Economy

[petkovski]

Yesterday I noticed some bad vibrations on this motor at around 4000 rpms. It doesn't mean that they aren't there at lower or higher rpms, but at 4000, I can tell that they are there, they even transfer to the hull and I can feel the whole boat vibrating. Ordinary people will not notice them, but I definitely do and it's driving me mad. I know that there are lots of things that can go wrong, but I'm asking for just a suggestion for the usual things that I should inspect. (My dad suggested that maybe is got something to do with the lower unit oil, as we haven't changed it recently, and maybe it got 100 - 150 hours on it).

Also, I want to ask about the fuel economy for this kind of engine. It's fitted on a 15 foot - 1060 pound boat. I'm getting approx. 5 to 6 gallons per hour if i cruize at a constant speed of about 3800 - 4200 rpms (17 - 19 mph). If I go at full speed 5000+ rpms, then the consumption is 7 to 8 gallons. The boat load is 2 persons + equipment. Is this normal? I know that older 2 strokes engine can drink alot of fuel. I use 95 octane unleaded fuel.

If the fuel consumption is high, what are the appropriate actions one must take? Clean carbs, fuel lines, filters, etc?

Thanks.

 

[petkovski]

Update:

I've changed the lower unit oil. No water in it or metal particles. It was black and smelt awfull. I made a test ride with the boat, but the vibrations still occured, most notably at 4000 rpms. Still don't know what's causing them. I've checked for loosen screws and parts, steering mechanism and the propeller. No problems whatsoever.

Also, can someone tell me why my trim gauge is not working? I've checked for disconnected wires and bad contacts, but everything seemed to be in place.

 

[petkovski]

One more thing. Why the alarm buzzer goes on everytime I cold start the engine? It beeps (beep beep beep beep beep) - fast, then a short delay then again and again, until I put it into gear. The next time I will start it up, it starts right away with no alarm. This happens ocassionally, and not everytime I start the engine. I don't think it's the VRO alarm since the VRO it's working and the oil tank it's full.

 

[WernerF]

Fuel consumption sounds not too bad. Rule of thumb for two-strokes: 1/10 of hp rating is fuel consumption (gal/h) at WOT. Cruising speed (boat planing?) seems a little slow for a 70hp 15' boat. My 17' can't plane that slow.

I had this occasional alarm sound at engine start on my 1989 60hp (same engine except carbs). It is the VRO alarm circuit which fails to reset at power-on. You can verify the VRO causing the alarm by pulling its 3-pole connector when it happens again. The problem can be solved, but experience on electronics is required. But it's not really necessary as the alarm reliably stops with the first oil pump stroke. Actually you can let this behaviour work for you as an additional test of the VRO alarm. For the complete story look here: http://forums.iboats.com/johnson-evinrude-outboards/vro2-question-about-no-oil-flow-alarm-538948.html

It's almost always the trim sending unit that is bad if the trim gauge fails. Unfortunately the trim sender is not available anymore. It's located in the bracket on the port side and has a lever that "feels" the trim angle. If you are lucky it's just stuck and you can free it with WD40/grease etc. Essentially it's a 600 Ohms potentiometer, but only the part between 0 and 93 Ohms is used. In my engine the pot had a crack, so I scratched out the potting and replaced the potentiomenter with a 500 Ohms 4W 280° wire-wound type. Well most people would say: Trim by feeling!

I have no idea about the vibrations. It's almost impossible to find any unbalancy other than the propeller. Maybe your boat exhibits a resonance at 4000rpm (67Hz). The rubber mounts could have been hardened. Are you sure all cylinders a firing over the whole trottle range? Do all three spark plugs look the same (after some time cruising)?

 

[petkovski]

Fuel consumption sounds not too bad. Rule of thumb for two-strokes: 1/10 of hp rating is fuel consumption (gal/h) at WOT. Cruising speed (boat planing?) seems a little slow for a 70hp 15' boat. My 17' can't plane that slow.

Cruising speed is definitely 17 - 19 mph, 3800 - 4200 rpms. Max speed is around 30 mph, with the trim set just at the right angle.

I had this occasional alarm sound at engine start on my 1989 60hp (same engine except carbs). It is the VRO alarm circuit which fails to reset at power-on. You can verify the VRO causing the alarm by pulling its 3-pole connector when it happens again. The problem can be solved, but experience on electronics is required. But it's not really necessary as the alarm reliably stops with the first oil pump stroke. Actually you can let this behaviour work for you as an additional test of the VRO alarm. For the complete story look here: http://forums.iboats.com/johnson-ev...-question-about-no-oil-flow-alarm-538948.html

Yes, I thought so also. It's not a problem. Let it stay like this

It's almost always the trim sending unit that is bad if the trim gauge fails. Unfortunately the trim sender is not available anymore. It's located in the bracket on the port side and has a lever that "feels" the trim angle. If you are lucky it's just stuck and you can free it with WD40/grease etc. Essentially it's a 600 Ohms potentiometer, but only the part between 0 and 93 Ohms is used. In my engine the pot had a crack, so I scratched out the potting and replaced the potentiomenter with a 500 Ohms 4W 280° wire-wound type. Well most people would say: Trim by feeling!

Well, it's not a big problem, but I was just wondering why it's not working. I think i'm going to replace the gauge with one of Faria's fuel flow meters.

I have no idea about the vibrations. It's almost impossible to find any unbalancy other than the propeller. Maybe your boat exhibits a resonance at 4000rpm (67Hz). The rubber mounts could have been hardened. Are you sure all cylinders a firing over the whole trottle range? Do all three spark plugs look the same (after some time cruising)?

I will definitely check out the spark plugs, since they are new, I can tell if there's a problem with the firing sequence on all 3 cyls. Thank you for your reply, it's been very helpfull.

Since you have a very similar engine, can you tell me what kind of problems you have run into using it? I know that they are very reliable engines if you take proper care of them. I was hoping by the end of the season to clean the carbs and buy some seafoam to do a decarb.

Cheers.

 

[WernerF]

What pitch propeller do you use? I have a 15" pitch prop on my 17' open cabin boat, so I expect a 17" pitch prop on your 70hp 15' combination. Thinking about theoretical speed and prop slippage...

I got my motor 4 years ago and have cought up on the work the previous owner neglected. The motor had been run in saltwater for ten years, but I'm running in fresh water again. This is my history:
1. Bought a factory service manual here on marineengine.com
2. Water pump (of course) and thermostat.
3. Rebuilt the carbs, but they were clean; it didn't improve anything. I guess, way too many carbs are rebuilt.
4. Trim/Tilt keys on the starboard side of the lower cowling. This thing is really overpriced. But it can be cut apart, contacts cleaned/greased and glued together again with 2-component epoxy glue. Works perfect and nothing can be seen from the outside.
5. Rebuilt the trim motor. No brush/seal kit available for the BOSCH trim motor. I found a company in Germany selling all kinds of carbon brushes. Another company cut the gaskets. Getting the tilt pin out of the saltwater engine was really hard.
6. Trim sender.
7. Replaced the reeds with Chris Carson reeds. Wasn't really necessary, but I was trying to fix a top carb fuel spitback issue. Now I know it's pretty normal for this engine. The reeds did make idle a little better.
8. Replaced the power pack. Had an intermittent miss on all three cylinders at high rpm. Maybe false SLOW mode. Was really tough to find, took me half a year.
9. Replaced control cables, key switch (didn't spring back from start position) and buzzer (weak tone, sometimes none). Repaired the broken plastic domes (for the trim/tilt switch) in the throttle lever with some pieces of aluminum tube and epoxy glue.
10. Repaired the VRO alarm circuit. The new buzzer made the false alarm issue really bad. Some ratchet clamps around the VRO oil hoses were broken.
11. Relocated the tell tale hose fitting to the top of the exhaust box. There is a OMC service bulletin recommending that, because of air that might be trapped in the cooling system.
12. Replaced the rectifier with a rectifier/regulator, because my VHF radio complained about overvoltage.
13. Lower unit reseal. I haven't got the special tools for pulling out the bearing housing, so I have that done by a mechanic.

All in all the engine runs pretty good. Plenty of power, good hole shot. Idle could be more stable. Idle rpm depends a little on the outside temperature.

Some steaming out of the exhaust relief ports is pretty normal. It depends on the weather and exhaust temperature.

 

[Jerryjerry05]

Start the motor on the hose. Then put it in gear and see if there is a wobble. Oh yea take off the prop first. It should turn with NO wobble at all. Then put the prop on and see if it turns true. Do a compression test. To see if the prop is the right one, run it at wot and check the rpms. I think 52-5500 is the max you should be running.Post your results.

 

[petkovski]

What pitch propeller do you use? I have a 15" pitch prop on my 17' open cabin boat, so I expect a 17" pitch prop on your 70hp 15' combination. Thinking about theoretical speed and prop slippage...

I got my motor 4 years ago and have cought up on the work the previous owner neglected. The motor had been run in saltwater for ten years, but I'm running in fresh water again. This is my history:
1. Bought a factory service manual here on marineengine.com
2. Water pump (of course) and thermostat.
3. Rebuilt the carbs, but they were clean; it didn't improve anything. I guess, way too many carbs are rebuilt.
4. Trim/Tilt keys on the starboard side of the lower cowling. This thing is really overpriced. But it can be cut apart, contacts cleaned/greased and glued together again with 2-component epoxy glue. Works perfect and nothing can be seen from the outside.
5. Rebuilt the trim motor. No brush/seal kit available for the BOSCH trim motor. I found a company in Germany selling all kinds of carbon brushes. Another company cut the gaskets. Getting the tilt pin out of the saltwater engine was really hard.
6. Trim sender.
7. Replaced the reeds with Chris Carson reeds. Wasn't really necessary, but I was trying to fix a top carb fuel spitback issue. Now I know it's pretty normal for this engine. The reeds did make idle a little better.
8. Replaced the power pack. Had an intermittent miss on all three cylinders at high rpm. Maybe false SLOW mode. Was really tough to find, took me half a year.
9. Replaced control cables, key switch (didn't spring back from start position) and buzzer (weak tone, sometimes none). Repaired the broken plastic domes (for the trim/tilt switch) in the throttle lever with some pieces of aluminum tube and epoxy glue.
10. Repaired the VRO alarm circuit. The new buzzer made the false alarm issue really bad. Some ratchet clamps around the VRO oil hoses were broken.
11. Relocated the tell tale hose fitting to the top of the exhaust box. There is a OMC service bulletin recommending that, because of air that might be trapped in the cooling system.
12. Replaced the rectifier with a rectifier/regulator, because my VHF radio complained about overvoltage.
13. Lower unit reseal. I haven't got the special tools for pulling out the bearing housing, so I have that done by a mechanic.

All in all the engine runs pretty good. Plenty of power, good hole shot. Idle could be more stable. Idle rpm depends a little on the outside temperature.

Some steaming out of the exhaust relief ports is pretty normal. It depends on the weather and exhaust temperature.

I bought the boat from Germany 5 years ago. Campion Allante 160 with a 70 Evinrude, but only got the opportunity to drive it now. I know that the old man drove it only one week every year on the Adriatic. He's the first owner. The usual maintanance has been done. Gear oil, spark plugs and preparation for winter. I've noticed that the engine has been preserved in some kind of wax / grease, but don't know when.

Everything seems to be working as should. I've changed the lower gear oil, no water or other debris in it. Changed the spark plugs. First time starting was a little hard. Had to put alot of fuel additive to get it into perferct running condition. Now it starts right away, even when cold. I've noticed that at low RPM it's a little shaky. Idle is around 1000 - 1100 RPM, and when you put into gear it's 700 - 800 RPM. I always let it run for about 5 minutes to warm it up before going WOT. Haven't checked the compression, but I think it's fine since it's not driven more than 200 hours.

I'm planning to rebuild the carbs, and reseal them. I've noticed small fuel leakage, 1 - 2 drops of fuel everytime I drive it. Also do the decarb thing with the SeaFoam. Once this is done, I think that the idle will be more smooth.

I've also noticed small oil leakage beneath the VRO. It's VRO2. There's a small white filter beneath it. Do you happen to know how often this filter should be replaced?

Here's a picture of mine. I did a custom paint job couple of days ago. The old one was scratched and lost it's shine



Cheers

 

[petkovski]

One more thought about the vibrations. When I did the paintjob on this thing, I've removed the foam that covered the inside. This foam used as an sound silencer, and now without it, at 4000 rpms there are vibrations caused by sound bouncing off and on inside. Definitely the cause!

 

[WernerF]

I've noticed that at low RPM it's a little shaky. Idle is around 1000 - 1100 RPM, and when you put into gear it's 700 - 800 RPM.

That's ok, my engine does the same. Idle is worse when the weather is hot. If the engine stalls in gear, there is some work to do.

I've noticed small fuel leakage, 1 - 2 drops of fuel everytime I drive it.

Most likely the fuel comes out of the air silencer. This plastic thing and its gaskets are never perfectly tight. The carbs spit back a little fuel, that's normal. Most of it is recirculated into the bottom crankcase. But a little drips out.

I've also noticed small oil leakage beneath the VRO.

It could be mix fuel that vaporizes and you see the residual oil. Check the hose clamps on the oil hoses. Some of them were broken on my engine. OMC demands to use special ratchet clamps, because tie straps are not reliably tight and metal worm clamps can damage the hoses. It's important that the oil supply is air tight since oil is thick and the VRO would suck air much easier than oil.

Do you happen to know how often this filter should be replaced?

The manual calls for replacement once a year. But many boats have installed another water separator/fuel filter. If so the inline fuel filter isn't that important. It just shouldn't dissolve in fuel due to age.

Happy boating!