Cannot engage boat engine in water?

Question

I have a 70 hp evenrude engine on a 17 ft boat.

It does not have a trim and tilt unit.

The engine starts up fine above water runs well. Reves high

and engages properly

When I put the boat into the water I have the tilt all the way down.

I try to put it into reverse and the engine stops.

When I try to put it in forward and begin to increase rpm it stops again.

Always restarts.

It only happens when it is in the water. Otherwise it runs without problem.

all three carbs were redone recently. compression is good.

Do I need to have the tilt of the engine higher when starting to rev up the engine???

New to boating so looking for answers.

Answer 1

You have underwater exhaust;  this makes it possible for the motor to run fine out of water then run like c**p with the lower unit submerged, because of backpressure on the exhaust.

Sounds like you just need to link & sync -- or else increase the idle speed a touch -- were the carbs rebuilt by a certified marine tech, or was it a DIY job?

Take a look at the starboard side of the engine, look for a flat triangular metal sort of plate that rotates forward when the throttle control is advanced -- that's the "throttle cam".  

The cam contacts a roller (the "cam follower roller"), which is what opens the throttle butterflies in the carbs.

There's a mark scribed on the leading edge of the cam -- when the cam hits the roller, it has to be right on that mark.

If it hits too soon, the throttles will open before the spark timing has advanced, with the result that the engine will not accelerate.

Notice the throttle lever, thing the throttle cable is attached to -- there's a set s***w with a spring-loaded nut just below the lever pivot point -- that's your idle set s***w.

It should idle at 950 - 1000 RPMs in neutral with the lower unit submerged, and around 800 RPMs in gear.

Out of the water, idle speed will be a couple hundred RPMs higher, due to the backpressure.

**********  IMPORTANT  ***********

NEVER, BUT NEVER start your engine without supplying water to the lower unit water intakes -- it only takes about 45 seconds of dry running to ruin your water pump impeller.  If the impeller fails while the motor's running, the engine will heat up and seize in a matter of seconds.

NEVER, BUT NEVER rev your motor above 1500 or so without submerging the lower unit (except as needed to warm up a cold engine).  Without backpressure on the exhaust, you risk thermal runaway, in which the engine will race out of control and there's nothing you can do except unplug the fuel line and hope the carbs run dry before it tears itself apart.

Answer 2

dude you got me on that one

but what i would do is raise the idle if its to low  it should be750 to 1000 rpms also did you put to much oil in the gas, change the spark plugs change the water sepperator if you have one and also check the fuel vent make sure its venting nothings blocking it