please help!!!!

[dave69larson]

Hi first I am new to this forum, I have a 1969 larson 18ft 120hp inboard. I recently recieved as a gift. I have a couple of different ?'s

First last time I had it out with tow people in, it ran fine got up on plane farily quick and did about 30mph with a 3 blade 15 pitch prop. Then after a bit went back and pick up a total of four people and the boat took a bit longer to plain but it did. After fishing for a bit we went to take off but the boat would only rev up to 3000 rpm and felt like the boat was too havy in the back end or the motor was bogging.
So questions are is a 3 blade 15 pitch good enough to run on there or should I be going with something bigger, at wot it will rev to 5000 rpm but I only took to 4500 when I was givener. I am guessing that it should run around 4500 rpm at wot.
2nd I did a compression test and the cylinders ran between 105 and 80 at the lowest, is that sufficent to create enough power?

one other question is I was looking at the bilge area and the front of the bilge area is open to the bottom of the boat. There is about a 4 inch drop to the bottom of the boat . Should that be open to allow water at the front of the boat to come back or should it be sealed.
Any help would be great and as fast as possible my summer is going fast.

 

[jtmarten]

Re: please help!!!!

If it hasn't been done, or you don't know when last done, a tune up would be a great idea; plugs, points, cap, rotor, oil change, impeller, etc.

15p is a pretty small prop, you should have no problem spinning it faster.

Compression test: done warm? coil wire grounded, plugs out, WOT?? If not, you'll get very low numbers.

A tired 120 in an 18 footer with 4 people is gonna take a while to plane. The foam in the hull may be waterlogged if it sat outside in the elements, which adds alot of weight.

The area around the engine, between stringers, is usually open. You should have drain channels coming from the front of the boat on each side, make sure they're not plugged and holding water up front. Yours may just be open to the bow if you don't have a bulkhead there.

 

[dave69larson]

Re: please help!!!!

compression test was done cold, I will do one warm soon. I had the coil wire off and took one plug out at a time. I am guessing the comp should be around 130 psi.
I don't think there is any tubes coming from the front of the boat, it is just open and has a 4 " drop to the bottom of the boat. So that is normal??

 

[dave69larson]

Re: please help!!!!

oh ya have done full tune up and checked timing engine is running smooth no misses.