NO thrust with 200hp EFI

[Miniton]

I have a 1984 Blackmax 200hp EFI. Motor runs perfect and starts everytime. When I go full throttle from idle for during holeshot it seems like the propellor and motoer are fully engaged and rev up but I don't go anywhere unless I back off and do a slow throttle. It is like the propellor is spinning out of the water.
It also does this during sharp turns while throttling.
Can anyone help me pinpoint the possible causes?

Thx in advance for any help.

 

[pmat1]

Re: NO thrust with 200hp EFI

Im rather new to boating but it sounds like a Spun prop?

 

[cannonford57]

Re: NO thrust with 200hp EFI

is engine on a plate?possibly too high on transom.....what kind of boat,setup do ya have?

 

[Miniton]

Re: NO thrust with 200hp EFI

1984 Astro 20FSX Fish and Ski. No Jackplate. Motor is mounted on middle hole of five on mount. It has an aluminum 21 pitch prop.
It only happens when under load. If I am just casually cruising it runs great and tops out at around 60mph by speedo.

Thx for responses so far

 

[cannonford57]

Re: NO thrust with 200hp EFI

each hole is 3/4 inch up or down...could be a simple matter of dropping 1 hole and everything could be peanutbutter and snot...(thats suppose to be a good thing)the prop is another issue alltogether,what kind of shape is it in...1 blade out of track could cavatate the prop in a turn......hope it helps