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View Full Version : Outboard dies under throttle, but is fine at idle. Please help!



ccrogue14
29-10-2014, 02:00 PM
Engine: 1976 Johnson 70HP

A few days ago my boys took the boat out fishing and ran out of petrol on the water. They had some backup fuel with them, but not enough, so they decided to add some bottled water to the fuel tank and mix it with the remaining fuel/oil (not smart).

Ofcourse that didnt work and the engine didnt start. Eventually they got towed to shore and brought the boat home.

I drained the fuel tank completely and added fresh fuel/oil, removed the plugs and dried them out - then the engine started and was idling like before. I tried reving the engine up whilst in Neutral and it revs fine.

I then though everything was fine so I took the boat back to the water to test it.

Engine started fine and was idiling without any issues, so I put it into gear and kept the revs as low as possible. The engine was running ok.
I then applied throttle a bit more and the engine died. I tested it a few more times, the same thing happened.

I brought the boat home and removed the entire carby (including the float sump), cleaned it (although it was already quite clean) and dried it with an air pressure gun. I cleaned and dried all fuel hosing. Assembled everything back, but the same issue occured.

What else should I be looking at? Am I missing something?

Please HELP!

astro66
29-10-2014, 04:36 PM
first thing...new plugs....

GBC
29-10-2014, 06:14 PM
Those babies had problems with pinholes in exhausts. If you can take the cowl off and she goes under load ok it is a dead giveaway. Put the cowl back on and it doesn't bloody go. Drives you bloody mad trying to work it out too.

paullee
29-10-2014, 07:12 PM
I had an old 70 that used to do the same thing intermittently. We thought carby problems for ages and yours probably still is due to the circumstances that brought the fault on (assuming all was fine before the water issue?) Mine turned out to be a faulty ignition coil or 2- from memory they had cracks in them and would arc out under load (so to speak). Picked it up by trying to find it one late afternoon on the water while it was getting dark. Could see the coils arcing not where they were meant to be!! Have you drained all fuel from carbys and lines and ran motor from seperate fresh jerry can?

littlejim
29-10-2014, 07:47 PM
The fuel filter up under the cowl can also cause a similar problem if it is gummed up with cr*p.
recommend you go to a lot of trouble to find the cause.
My identical evinrude 70HP was completely r**ted because the servicing mob didn't change the aforementioned filter. (they then went out of business, so no comeback.) The engine ran lean and melted some important bits.
the replacement cost a lot of biccies.

Noelm
30-10-2014, 07:41 AM
There is a couple of probabilities here, are you sure it ran out of petrol? maybe it just died, and the fuel was low so they/you thought it had run out? Regardless, putting water in the tank was never going to end good.....you may have to replace any filters in the system, remove the carbies and clean them properly, not just wash and blow them out with air, but, before you do that, what do the plugs look like? black and oily, or dry and white? are they all the same? you need to do some very basic trouible shooting first.

ccrogue14
31-10-2014, 07:46 AM
- I put in a set of new plugs
- removed the 3 carburetors and cleaned them with cleaner and metho then blew air into it with air compressor to dry it all out
- changed all the carby gaskets
- removed fuel pump/filter and cleaned then fitted new gaskets (it was pretty clean anyway)
- dried all fuel lines
- emptied tank, put new fuel in tank
- checked for sparks, ok
- flushed the gearbox fluid

The weird thing is that if I test it at home with the earmuffs, it runs smooth like a dream - both at idle and in gear

The moment I drop her in the water and test again, it runs smooth at idle but stalls when in gear and throttle is applied.

Steeler
31-10-2014, 09:32 AM
Just throwing it out there but you say it idles fine on the muffs but not once the exhaust is submerged in the water. Have you taken into account that once the exhaust is submerged the back pressure on the exhaust can have quite a downward effect on idle speed.