93 evinrude 120hp trouble getting on plane

[cold_gin]

How many RPMs should i expect when i accelerate to try to get on plane? With the motor trimmed all the way down and going full throttle im seeing 3000 rpm. and wont plane at all. Ive had this boat since 2007 once in awhile ive hand to have my passenger move toward the front to lessen the load in the back. This boat never was really quick to plane but it is definitely having problems now. The last two times Ive taken it out ive had to move to the front to get it to break over. Once the boat starts to go the rpms jump up and i see 5600 rpms and the boat started to porpoise until the motor trimmed up. Once i got her to plane and the trim in a good spot she ran fine.

 

[phillnjack2]

Re: 93 evinrude 120hp trouble getting on plane

what size and type of prop ? this could be far too big for the hole shot
(but can be made better once we know what it is)

what size and weight of boat ?
where is the centre of gravity of the boat ? ideal would be 1/3rd of total length of boat
(easy to find out by rolling it back along trailer until it starts to tilt )

I ask this as could all the back of the boat be extra heavy?
is there a cavity under the floor that has lots of water in there making it all flow to the back before the boat levels out. ?

how high on the transom is the engine mounted ?
where is cavitation plate in relation to bottom of the transom centre ?


phill

 

[cold_gin]

Re: 93 evinrude 120hp trouble getting on plane

16' 8" javelin bass boat, has a stainless turbo 20 degree prop (was on it when i bought the boat) bilge is dry, in the back there are 3 batteries and a 20 gallon tank.

It used to be able to get on plane sorta ok so i havent measured anything

 

[phillnjack2]

Re: 93 evinrude 120hp trouble getting on plane

now 3 batteries and a 20 gallon tank sounds like a lot of weight to be honest.
now if the tank is full and it used to be just half full is a lot extra ?
have you moved any of the batteries and placed them further back ?

is the engine compression good ? what are the numbers for each cylinder etc ?

now being as its never been great for hole shot, what about getting the prop vented (drilled for take off issues) ?
this will make the prop react like a much smaller pitch during zero to plane speeds, then normal prop once up and running.

is a very easy thing to do and don't cost anything and don't ruin anything.
just a simple drilling of holes between each blade down at bottom of hub is all that's needed.
it lets the engine get upto revs and that = power = acceleration from zero.

here is what I do, just drill the holes 1/4 inch diameter and test, if only a touch better I then go upto 3/8ths then test and finally 1/2 inch.
your engine should swing that prop easy enough if its a 13 diameter, but if its a 13 3/4 it will need to be drilled to give good hole shot.

its either that or a new prop with smaller pitch and possibly diameter as well.

pics below
show what I done to get good hole shot from a prop that realy wasn't good before I drilled it.


phill
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