Marine Forum

Evinrude 1977 70HP - Throttle Issues

majed1965

12 February 2007 08:03:44

Joined: 12 February 2007 08:01:51 | Posts: 1

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.

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?

---

Majed

Re: Evinrude 1977 70HP - Throttle Issues

Anonymous user

23 March 2007 10:44:37

Joined: Unknown | Posts: Unknown

Hi there,

I am a marine mechanic who has spent a lot of time around these old engines and have a few suggestions:

You indicate that the problem is linked to time or temperature.

Because it is #1 cylinder we have to consider what it has separate to the others.

I am thinking fuel pump because it is easy to diagnose and #1 runs out of fuel before the others because of gravity. - To diagnose squeeze primer bulb when the problem occurs and the motor should be ok until it runs out of fuel again.

There are metal screens both on the fuel pump cover, and the fuel tank (if it is a factory tank). Both are easy to check.

Flooding could be an issue on one cylinder too, because of separate carbs and the diagnosis is to have the motor on a slight tilt, with the air box cover removed and squeeze the primer bulb tightly. - Remember after doing this that the fuel system will be pressurised and fuel may spray if components are disconnected.

Another issue is crank-case compression, an essential element in two stroke engines. Normally this would only affect low engine speeds, causing the cylinder to miss and pop, indicating lean fuel. On the top cylinder a likely culprit to cause this would be the top crankcase seal. If this is leaking you will see thick black oil running down the block from under the flywheel region.

Apart from that, the other things I can think of (I have retired from outboards so I am rusty) is ignition. These engines are the only ones in the range which have a separate sensor coil for each cylinder so it is possible that one of them is cutting out under load and/or heat. Also in the CDI unit there are separate components, plus wiring and coils.

1977 was a time of major model overhauls for Outboard Marine and you will either have an older-style ignition module with screw on terminals or the later one in the plastic case with water-proof amphenol connectors.

To diagnose the ignition you will need a spark checker because checking for spark across a short gap in normal atmospheric conditions is not good enough. Coils you can swap, earths and general wiring you can check.

One problem with these older models is in the main harness plug, which is generally red and under the cowling. Sometimes a black tracking mark can be seen across terminals where short circuits have occurred. Your symptoms do not quite fit this problem though.

I hope this sheds some light on your problem, I am in Wollongong and can organise a time to talk to you over the phone, if necessary.

Roger Barnes

Re: Evinrude 1977 70HP - Throttle Issues

Anonymous user

23 March 2007 11:42:16

Joined: Unknown | Posts: Unknown

What great reply! 10/10 ****

Re: Evinrude 1977 70HP - Throttle Issues

Anonymous user

21 June 2008 07:44:46

Joined: Unknown | Posts: Unknown

Hi, I too have exactly the same year boat and motor. Your suggestions are AWESOME and make perfect sense.
However, I did try and replace my spark plugs that were clearly worn out. THis seemed to fix the problem right up.
Had exactly the same symptoms. I would take off fine, then after about a minute on the water at full throttle, the boat would simply cut back as if i were at 1/4 throttle.
Thanks all!

Re: Evinrude 1977 70HP - Throttle Issues

Anonymous user

09 March 2009 01:01:10

Joined: Unknown | Posts: Unknown

Hi I have a Johnson 70 on a Nautiglass as well and mine was doing the same sort of thing but only in reverse. Would not get up to speed and was running on 2 cylinders until warmed up then the would all of sudden run on 3 and be fine. Found it was one spark plug that was faulty. I have another problem now and it has always had it to a degree. It is when i stop to fish the engine starts ok always but when put into gear it seems to flood and stop. I have since discovered buy accident out of the water that if the motor is trimmed all the way down the engine floods and smokes at idle. If i keep the engine tilted about 15 degrees above level it runs fine and when i went out on the water last time i made a conscious effort to keep the engine about 15 degrees above level and guess what it started fine everytime and kept going when put in gear. The only problem is that you need to have the engine below level to effectively use the trim to get up on the plane in quick time. Could someone tell me what is causing the flooding at below level when trimmed and how to fix. I am thinking my carbies will probably need to be rebuilt as the seat maybe worn but I am no expert. Thanks Graeme

Re: Evinrude 1977 70HP - Throttle Issues

Anonymous user

10 March 2012 06:52:35

Joined: Unknown | Posts: Unknown

its your power pack