1992 70hp Rude - Perfect except she dies at idle after idling for a few minutes

[JKTrevecca]

I have a pristine 1992 Evindrude 70hp on my 16 foot smokercraft. I couldn't be happier with this engine except when I'm using it for trolling umbrella rigs. At idle speed when trolling, it will die after idling for a couple minutes. It starts right back up if I give it neutral throttle but just doesn't want to run indefinately at idle speed. I pull umbrella rigs with about 100 feet of line out the back and when the engine dies, my rigs drop to the bottom of the lake if I don't get it re-started and accelerate quickly to pull them back up.


The engine runs like a top in all other area's. Is this something I should accept and live with or is there any tweaking suggested to make the engine idle more reliably and predictably?


The lowest I can idle is about 3.5 - 3.8mph. If, in the process of tweaking this, I would find a way to lower that speed to 2.5 - 3 mph, that would just be icing on top of the cake! Would trimming it all the way out slow the boat at idle speed? I may try that tomorrow to see what happens.

Thanks in advance. Grace and Peace!

 

[racerone]

Is there a thermostat installed and is it working properly ?-------Does the tell tale hose come off the side of the block or the top of the block ?-----What fuekl are you using ?

 

[BonairII]

sounds like the carbs need a cleaning. The low speed circuits may be clogged a bit. Trimming it out will slow you down some because it will increase "prop slip" the nearer the prop gets to the surface of the water. But that isn't solving the problem...just treating the symptom.

Are plugs new(or in good shape)? Or are they carbon loaded from all of the slow trolling?

 

[JKTrevecca]

Thanks for the replies! No clue about the thermostat. This motor is un-touched so if it came with one originally,it still has it. As far as whether it works, how can I tell? I have a very strong water pump and have no other symptoms besides the dying @ idle speed. The tell tale hose comes off the top of the block and down to the right rear side of the cowl. I use 87 octane fuel. A couple stations near here sell "non-ethanol" fuel but I usually just buy the same stuff I put in my cars which may have some ethanol in it. I use wal-mart 2-stroke oil too if that matters.Always have. I removed the plugs and have attached photos. I'll let you guys give me your opinions on those if you don't mind. The plugs in it are champion's. They look "normal" to me for a 2-stroke. While I had them out, I did a compression test for the heck of it. I have 110 psi on all 3 cyl's. Is that low? My old mercury 40hp had 150 psi on both cyl's so 110 seams a little low but it was uniform across all 3 cyl's.

Any suggestions other than maybe cleaning the carbs based on this response? Thanks again!

-- Jason

 

[Chinewalker]

Pull the cap off the top of the cylinder head and double check that the t-stat is there. Won't take but a few minutes and if you're lucky, you won't even damage the gasket.

 

[JKTrevecca]

Thanks for taking the time to reply chinewalker. I appreciate it. So if I pull the head off and find no t-stat, can you help me understand how that would cause the issue i described? Would the lack of a t-stat just let the motor cool too much when it should be kept warmer to idle well?

 

[Chinewalker]

That is correct. And it's the cap at the top of the head, not the head itself you'll be removing.