Why is this thing so hard to start? (in the water)

[egclassic]

1977 70HP Johnson.
I have done alot of work to this motor since I bought it a couple of months ago, nothing major, just bringing it back to life.
Here is the issue: at home on the trailer, this thing starts right up whether I run it on the muffs or in my 55gal. flush tank.
At the ramp, it takes forever to get started. Sometimes I'm afraid I'm going to kill one of my batteries just getting it started.
A little history; I have rebuilt all 3 carbs(carefully set the floats), rebuilt fuel pump, replaced all fuel lines (interior & exterior), replaced all 3 coils, replaced and properly gapped spark plugs, de-carbed engine(following procedure in "top secret" folder), and performed the lync 'n sync.
I have checked compression a couple times now and get 120 on all 3.
I have checked the spark (after replacing coils), easily jumps 7/16"
My start up procedure is: squeeze primer bulb until firm, lift warm up lever, push key in and crank.

 

[hornblower]

Re: Why is this thing so hard to start? (in the water)

Question, Are the exhaust port holes on the back of the motor under water? (Is the motor a little heavy for the boat?)

 

[egclassic]

Re: Why is this thing so hard to start? (in the water)

Question, Are the exhaust port holes on the back of the motor under water? (Is the motor a little heavy for the boat?)

No, the ports are above the water.
As far as the motor being too heavy, the boat is rated for a 65hp. But as I stated in another post, I found 65hp motors that weighed more than this one. This motor I believe weighs 230lbs.
Besides, when I back the trailer into the water to start the motor, I only back in until the water is just above the Cavatation plate(maybe a bit more). This way there is minimal backpressure, but still enough to more than cover the water intake.
Forgot to mention, once it has warmed up, it starts right away on the water.( Unless we sit for a long time.)