High Altitude to Low

coxhaus · Jul 28, 2015

I just picked up my wife's cousin's boat which is a Mirrocraft Outfiters with a 70 HP Evinrude and a 9.9 Johnson trolling motor. My wife's cousin bought the boat new in 1987. He then sold it to his best friend. I, in turn, bought the boat from his friend. It is nice knowing the history.

My question is this; the boat lived in Colorado at 5000 feet and now I am taking it to Texas to live so is there anything I need to do to the motor because it is now going to live at basically sea level? I received several props and was told to run the 19 pitch prop in Texas and Canada. I have been going up to Canada the last several years fishing since I am retired now.

kofkorn · Jul 28, 2015

It's going to run leaner at the lower altitude, which won't be a significant issue unless it was jetted for the higher alt. Check the plugs and take a picture. After you've run it for a while, take another picture and compare. If you see a significant difference, you may want to change to a different temp plug and consider replacing the jets with stock ones. Can you remove the jets and look for a number stamped on them? That will tell you if you're running a custom jetting.

Shouldn't be a really noticeable difference when running at high speed though.

I had a 1981 Honda CB900 that used to foul plugs every couple of months. When I moved to MA, it leaned out and I never had a problem again. Wasn't a significant elevation change, but it made a difference.

Pappy · Jul 28, 2015

By all means!
Before you run it the high speed jets need to be checked and verified that they are the correct ones for sea level operation.
Go to marineengine.com and look up your engine by model number and year and check them,
If you need help we can help you here.
If you are running the correct jets for 5000' there is a good chance you will stick pistons at sea level.
Since it was purchased in 1987 am not sure whether the engine would be an older or newer one. If it is a 56 cu.in. block those are more sensitive than the older 49 cu.in. blocks. The changeover years started around 1986.

coxhaus · Jul 29, 2015

I tried to figure out which Evinrude 70 I have but I can only read the E70 off the plate. The numbers after E70 are not readable but I know the motor is a 1986. There seems to be an E70E and an E70T. What is the difference? Can I tell by looking at the motor?

PS
I can read the serial number if that would help.