'78 Evinrude 70hp dies under load

[BigBadStang]

Hello, I have this engine that is driving me crazy! It will do anything I want it to do...starts easily, idles great, revs crisp, spins the prop in forward and reverse, but only in the driveway running in a barrel of water.
When I put the boat in the lake, it starts, idles and revs, but when it is put into gear, it will idle (although roughly and seemingly on the verge of dying), but upon trying to apply throttle, it bogs down and dies. Put shifter in 'N' and hit the key and it starts right up again. I've been unsuccessful getting the boat off the the trailer due to this.

The fuel tank is a new 12 gallon Moeller, new tank line and bulb, and new fuel lines under the cowl. (all this was replaced prior to me ever trying to start this engine). Compression is 118,117,120 respectivley.
I know this has to be something minute, due to how well it runs otherwise.
The boat does have an aftermarket 2 lever control that has no provision for a warm up lever, and the electric choke is functional. I have let the engine run for 5-8 minutes prior to putting the engine under load with the same result.

Any pointers to get me going in the right direction without throwing money and parts at it would be greatly appreciated. Thanks in advance.

My biggest obsticle is my boat is some 3 1/2 hours from my home, so I have to do repairs on it when I am at the lake house, so my results from suggestions could be a little slow.


Thanks in advance!

 

[jonesg]

Re: '78 Evinrude 70hp dies under load

Buy a spark gap tester at an auto parts store, set it to 7/16th inch and test the spark, should jump with strong blue spark, not yellow.

If it sparks good then I'd rebuild the carbs with new kits.

It could be weak spark of clogged carbs.
You may want to install a water seperator too.

 

[Fisherball]

Re: '78 Evinrude 70hp dies under load

Is your fuel tank vent open? Sounds like it could be something that simple. I had to get towed off the water o1st time I used a new partable tank cuz I didn't know to open vent tap!!!

 

[BigBadStang]

Re: '78 Evinrude 70hp dies under load

Buy a spark gap tester at an auto parts store, set it to 7/16th inch and test the spark, should jump with strong blue spark, not yellow.

If it sparks good then I'd rebuild the carbs with new kits.

It could be weak spark of clogged carbs.
You may want to install a water seperator too.

Ok, thanks. I talked to a local, and he kind of thought the same. Probably a carb problem, float level, blocked passage or jet. I've read not to dip the carbs in carb dip due to the anodizing, and the sealer in the carbs. What's the best stuff to use to clean out the passages and such?

Is your fuel tank vent open? Sounds like it could be something that simple. I had to get towed off the water o1st time I used a new partable tank cuz I didn't know to open vent tap!!!

Thanks for the thought. I did have the vent open though...but, I left the vent closed once, and the line connected to the engine, and as pressure built in the tank while it sat in the garage, it pushed fuel past the needle and seat and flooded it...lol.


Does anyone know what the buzz is about Sea Foam in 2 stroke outboards? Is it safe to use in older engines such as mine, or is there some other additive that works best since the fuels have changed so much.

Thanks guys!