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Evinrude 1977 70hp - Throttle Issues


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Posted - 06 Feb 2007 : 11:25:54 AM


Hi All,

I bought a Nautiglass Deep V Cuddy Cab over the weekend with a Evinrude 1977 70HP outboard. Its a good boat around 1987, and the outboard is an oldie 1977 model. It seems to be in good nick.

Took it out yesterday, and is stared first go. Let it idle for 5 mins to warm up and took it out onto the Georges River. It flew and got onto the plane quite quickly and comfortablly. After a few minutes i slowed down to turn back, it would not pick up speed. The throttle was put to the extreme, but it barely went more then 10km and hour. Went back to shore, and checked fuel lines which seemed ok. Mixture was fine 50 / 1 . Added a bit more outboard oil to tank and went back out. Again it flew, but a few mins later it slowed down again. Rang the owner who i bout it off and he said he has not had any issues with it when he last took it out a week ago.

Can anyone please assist me with this issue. Maybe you have experience in this. The outboard sounded ok, pumped water fine. Looks good under the cover, no leak, no heat staining marks., etc. Thank you.

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It sounds like blocked carby jets, i'd replace the fuel filter and spray some carby cleaner into the chokes, then give it a few good revs... if that fails to unblock them then unblocking them gets slightly more technical and involves revving and blocking the chokes with your hand on the over run, otherwise you could just take it to your local marine mechanic

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I have been told that it maybe a tank breather problem. As the plastic tank i have does not seem to have a breather. If it is a breather issue, would it affect the throttle and power all the time or only when it warms up?

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if it is a tank breathing problem what is happening is that the tank needs possitive pressure in it. what it sounds like is that the tank is being sucked dry of all the air in it, which will affect the amount of fuel being drawn out of the tank.

this is maybe on problem

try running it with the filler cap slightly unscrewed this may help.

cheers T-Man

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Mate in all honesty in could be one of many issues causing the problem.

something small like Sammy said or possibly something major.

Or it could be something small that you could make bigger but continuing to drive it.

A simalr issue happened to me a while back on my first boat which had a Johno 140 1980 model.

It would run first off then after a while it would not go past 5 kms.....after cleaning carbi's, changing plugs etc i finally took it too a mechanic.

It turned out that the pistons were chipped and by continuing to drive it i had also damaged the crankshaft.

Now this is an extreme issue and hopefully is not what is happening to your motor but i think you should get a marine mechanic to take a look at it, or better still have one meet you at the ramp and have him jump on board....my marine mechanic met me at Picnic point ramp and found the problem.

Edited by netic
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From your description , it does sound as though the breather ( or lack of ) is the culprit. With any outboard newly purchased 2nd hand , it is always a good idea to have a marine mechanic check it out . I have a 76 55HP Evinrude , it runs like a champ , not bad for a 30 year old motor eh? :)


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Hi Majed,

Being a veteran user of 70's and 80's model OMC motors I have found that usually when it

appears something major has gone wrong it nearly always turns out to be something minor.

Your problem with it running then suddenly slowing down is almost certainly to do with not having

a air vent on the tank. On a warm day a sealed tank swells and creates presure that helps push the fuel out

once this pressure is gone the tank starts to cave in and eventually there not enough suction from the motor

to suck through fuel.

Was the bulb on the fuel line still full of petrol? Thats a dead give away that the tank needs to be vented it should always feel firm and fullof fuel. If the tank is vented and it still goes soft or empty theres an airleak somewhere in the fuel hose or bulb and it needs to be replaced

Also get the mechanic to replace the thermostat. If its never been changed or has ever been serviced by a non "oldschool" OMC mechanic they would have disabled, removed or tampered with the original thermostat thinking it was

running too hot. Unlike some other brands, the older OMC motors need to run very hot at idle to burn off the excess oil. If your motor occasionally stalls while idling or slow maneuvering, is then hard to start and blows lots of smoke when it does its running to cold.

Some tips on your style of motor - that have always got me out of trouble.

If using premix, when flushing the motor pull the fuel line clip off the motor

and run it until it stalls. If premix fuel is left to sit in the fuel bowl the petrol evaporates and leaves the oil behind making it harder to start and smoky. Oil injection motors dont need to do this as they run very little oil like 150-200:1 at idle whereas pre-mix is always 50:1

Ask your mechanic to give you back your old spark plugs from the service. This way you will have 3 know to be working spark plugs on your boat in case your out on the water and you think one may have failed. Also get a proper sized spark spanner thats suits your motor. Every second or third trip take the plugs out check if they are wet and give them a good clean with a petrol or aerostart socked rag.

Ask the mechanic to show you where the main fuse on the outboard is, and carry a spare. Its to the stern

of the fly wheel in a rubber snap lock. If the motor is completely dead and the battery is good it will generally be that fuse.

Carry a can of aerostart. Dont listen to people that say it will ruin your motor. If you are off shore and

cant start the motor you will be very thankful that you have it onboard. Its good for a few things, if the motor

is hard to start due to battery or other problems it will fire up start away with a 1 sec spray into the air cleaner. ( they usually have black rubber caps or some other way to access the air intake, you want to be able to see the top of the carbs so you can spray it directly into them ) Also it is the easiest way to work out whats causing a motor not to fire. If its turning over and not firing, and you spray aerostart in and it fires up straight away and stalls you can rule out electrical problems, it can only be fuel. Which then makes it easier to solve, as it can then only be a fuel or fuel flow problem.

If your out on the water and the motor wont start just remember that they flood really easy and sitting there and continuing to crank it wont help. Just wait five minutes ( check your watch when you are in a panic 30 secs seems like a long time ) and try and start it with no choke or warm up lever it will nearly always fire up . after waiting if it still wont fire crank it over with the leg/prop out of the water. This blows all the water out of the prop/exhaust and relieves the back pressure, making it easier to start. The prove of this working is Older OMC motors always start really well when you are flushing the motor out with the earmuffs on. Yet the same motor can be temperamental at the ramp. As soon as it starts drop the leg back in the water, it wont damage your impellor as it is still lubricated by water and a few seconds running out of water wont hurt it at all.

Check you overheat alarm on a regular basis Get you mechanic to show you how to do it- Its the brown wire that runs into the rear facing section of the motor, above the spark plugs. Ground this to earth with a pin and it will set the horn off , if it doesnt you need to get it checked.

If you not using it for a while, like over winter put the ear muffs on it once a month and start it up, lack of

use is what hurts these motors. It always makes me laugh the first day of good weather and you see people

down at the ramp cursing and swearing at a motor that wont start.

Have a big battery, with lots of reserve. My battery will crank the motor for a least 10mins (over 40 cranks )at full speed, your average car battery will only last 2mins at best. If it wont start in 40 cranks it aint ever going to start - If the battery goes dead after 5 cranks you'll never know... Also never remove the battery leads whilst its running it will damage the charging circuit. Forget about relying on pull starting it.... It will never work, try it at home with the ear muffs on then image trying to remove the cover, wind a rope around

and pull ( which will take several goes ) in a rough sea with the cowling off and water wetting all your electrics

Also remember to remove the cowling and spray the electrics with WD40 every few trips, grease all the nipples with a grease gun and oil the steering tube rod. Keep your WD40, Aerostart, Spark plugs & spanner, engine tools, fuses and other spares in a watertight bright plastic container in the boat, so in a panic you know where everything is.

The biggest thing to remember with old motors is that if it got you out there and it hasnt siezed or caught on fire it can get you home. Its being prepared and knowing what can cause the problems can mean the difference between you looking like a champ :thumbup: , impressing your mates and getting the motor running and heading home or looking like a chump being towed back by the coast guard ( or worse... :( )

Also learn how to contact the Coast Guard or Coastal Patrol (especially with an older motor) , and if you are having problems starting your motor give them a call, its free, they are volunteers and they love to help.

( if they do rescue you then a donation is always appreciated, smart arsed comments about it not being your fault etc wouldnt be... your the Captain EVERYTHING that goes wrong is your fault) You'd be suprised how these guys get spoken to by some of the once a year boaties, there the same ones at the ramp who are unbolting their cars battery to

Get their boat started

Anyway I know its a long post, but these things have really helped me over the years, and I only learnt through experience or listening to people in the know . Try and practise these things on dry land - you'll be glad you did. You'll always look like a pro when you get to the ramp, and your 1970's motor starts first time. :yahoo:

Also if you don’t have one, I have the Workshop manual that covers your boat in PDF format, even if you never Plan to work on the motor its good to know the basics about it and the fault solving and spark plug sections are a must read. PM me if you want a copy.


Edited by PPSGT
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Thank you all for the great tips. Will be taking the boat out for a spin with a recommended marine mechanic tomorrow. Will keep everyone informed of status. I really have learned a lot from everyone. Many thanks to all.

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Took the boat out this afternoon with a marine mechanic.

Prior to going out, compression check was done on the 3 cylinders with apparently good compression. Outboard was rated as good condition for its age. Pumps out water fine and sounds pretty normal.

Took off and gradually gave it full throttle. Absolutely flew onto the plane with ease. About 10 mins later we slowed down to turn back. This is when we lost power again. Boat would not pick up speed. Took us about 20 minutes to back to the ramp. Docked at the wharf where the mechanic started testing some things. The number 1 cylinder was not firing when the leads were taken out one at a time. Spark was coming out of lead, so electrical seemed fine. Cylinder 2 & 3 were fine.

Next was to put new spark plugs. Started outboard, and all cylinders were firing cause the outboard had cooled down. Went out again. but same thing happened again.

Tested compression again later and was fine. Even mechanic was dumb founded as he could not pin point the exact problem. Either piston is no good, cracked block or anything. Could be fuel problems to the number 1 cylinder when it gets to operating temperature.. Outboard was not overheating either. To start pulling it apart is a timely and costly thing and could end up costing more than whats its worth.

I am stuck and have no idea what to do. Sell boat as is, fix outboard or spend money on another one.

Has anyone had these sort of symptons b4 and can share with me?

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One thing i did notice is that the spark coming out the spark plug lead to the number 1 cylinder was very minimal when the engine was hot. When the outboard was cold all cylinders were firing fine. I'm no expert but to me it looked like only a really tiny spark was coming out when the outboard was hot. In a car engine you can actually hear the spark ticking. So i will check the coils and leads today and see how it goes. Hopefully they are not difficult to swap around for testing. Thanks.

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I took the coil out but couldnt complete it cause i was worried i would damage the wiring. From the coil side the wiring seems to be fixed into the coil, ie, there is no connector to undue. From the other end the cable goes into the powerpack and this also seems to be hard wired inside the pack. There are some bolts to undue which i think is the power pack, but i didnt touch it as it looks like it has a gasket under it. There other wire goes into some distribution board.

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We have had much needed rain the last 2 days in Sydney. Expecially today. Unfortunately these were my 2 days off from work and i have been unable to do any coil or power pack tests. Oh damn.......

Enquired about prices for the powerpack and coils. No one has any new ones, only second hand. The guy at the wreckers seems to think that if a coil or powerpack is no good they will not work at all. He seems to think that it would be something else otherwise the motor wont work at all. I have a feeling he maybe wrong as most people have informed me that these issues mostly arise when the parts heat up.

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I swapped the orange wires in the power pack and the engine didnt sound too good. was back firing and not idling right (hopefully hasnt caused any issues).

I swapped them back agin and it started ok. I ran in in idle for 20 minutes and used the hair dryer to heat the suspect coil, but to no avail. Motor idled perfectly and all plugs were firing. I would remove one at a time the plug leads in which the engine would react.

So i am not sure if there are any issues with the coils or power pack?

One thing i did notice what that the fuel hose into the fuel tank doesnt seem to be firmly tight on. I basically touched it and it released. It doesnt seem to go tight on. I also noticed a small fuel hose between the top abd middle carby cracked on the outside. It does not leak fuel but the cracks are noticable. Not sure if this would cause the issues i am experiencing with spark loss to plug 1.

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As you say you don,t think it's fuel

it is a elec problem i would say but i am no mechanic

when i road bikes a few guys had similair issues

they would ride and then bike would heat up and then blewwwwwwwwwwa

wouldn,t start until it was cold and got spark back

what was happening was the stator winds had a break in them and

until heat they would seperate but when cool they would join again

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they might be firing in a series but the 2nd one is taking out the 1st one

would it be possible to swap 1and 2 coil and then try it if it takes out the third plug then you might know the problem

don,t just change leads over

Edited by johnno
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Johnno - Will do that tomorrow as it is getting dark now.

I did notice when the outboard is idling, the least reaction from the engine when i pulled the lead out from the middle plug, but when your out in the water after ten minutes the top one has the least reaction when the lead is removed. Is it possible that the 2nd one can take out the 1st one when the engine is hot?

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not sure

but the thing is you need to eliminate stuff as you go or you will never know

it might be the 1st coil that is cactus

are your lead caps on the lead secure

also try swapping whole leads (not from plug to plug wrong firing order)over if possible as it might even be a lead thats breaking down

Edited by johnno
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My cousin who is a motor mechanic checked out the outboard on the ground today and found the engine to be in good condition. Idle'd well. Sparks were good. Compression was 120 in each cylinder, which apparently is good.

He found the coils to be suspect as they had cracks, and would most likely fail under load. He recommended we change all 3 coils and see how it goes. Hopefully if not, then will take it into the water on the weekend with a marine mechanic.

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!!!!!!!!!!!!!!!!!!!!!Problem Fixed!!!!!!!!!!!!!!!!!!!!!!!!!!

Took it to a wonderful marine mechanic at Picnic Point this evening.

1.Bottom coil was faulty as it was not giving out enough spark. Replaced with new one.

2. Top carby main injector was partially blocked. Cleaned out carby 1 & 2.

Ran boat again for about 15 minutes hard and didnt miss a beat. Mechanic informed me that engine is very good for its age.

One thing needs fixing which is the steering as it is a bit tight.

Thank you to everyone for your help.

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