Compression

[waterboy84]

I did a compression test on my 120hp force just to make sure compression is ok.
Cyl 1=155
Cyl 2=170
Cyl 3=170
Cyl 4=165
Do these number look ok for compression.
I personally feel like those compression numbers are high. However im not sure thats why im posting this to ask.

I did the compression test 2 different was.
I did both compression on a cold motor test.
Not cold as in outside temperature cold. I mean cold as in not running motor cold.
However i first did the test by removing one plug at a time.
Then the next day i did another test by removing all the plugs.
Compression numbers didnt change. They were the same readings .
Is the compression ok on my motor. Thanks for the info

 

[SkiDad]

Those numbers look great! it can depend on the gauge, but as long as they are as close together as yours are you are fine.

Mine are around 150 per hole last time I checked. I think the normal range is 145-165 with an accurate gauge.

have you verified the prop pitch?. You just need to go down a size if you are trying to get your RPM up.

also have you verified your carbs are fully opening ? at the end of the day 35 mph is still decent and will do anything you want to do on the water.

 

[waterboy84]

Hello skidad. We shall meet again. I appreciate the info. Yes i have looked and checked many times at carb butterflies. One of the carbs opens up perfectly flat. The other carb opens up just a tad bit past being flat. Not much past being flat at all.
Not sure if thats ok or not.
To the knowledge i recieved from a video that frank. From this website posted. The guy doing the video explains that both carbs dont have to be exact but close enough the be equal.
And witch the are both pretty equal expect one is perfectly flat and the other carb opens just a tad past being flat.
Boat is running good. I just want to make sure compression is ok due to the fact RPMs are still at around 4500 and boat is only running 30-35 mph.
I know force motors aint speed deman motors and i accept that. Not looking for speed.
Im just looking to make sure i have a great performing and depenable motor.
As far as the prop. When i purchased this boat the guy gave me a brand new prop for it still in the box. At that time i didnt realize or knew propers were important. So im not sure of the pitch of the prop.
Is there anyway of of identifying the info of this prop. I will post a pic of it and see if you can tell what it is.

 

[waterboy84]

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[SkiDad]

your carbs are OK.

it's usually stamped on the prop under the castle nut. Sometimes on the side of the hub. Your rpm seems indicate a 19p on there now (just a guesstimate)

 

[waterboy84]

So then basically what your saying is If this is the 19 pitch prop rpms and the mph is about all im gonna get.

 

[SkiDad]

well whatever prop pitch it is it might be best to drop down a size - so if it's 19 you should consider dropping down to 17. This will get your rpm closer to 5000. Chances are you will either stay the same speed or loose 1 mph. Your engine is rated for 4750-5250 at full throttle. This is kind of a touchy topic b/c 4500 is pretty close, some feel that getting it in the range will help your engine last better. My boat runs about 5500 and 37 mph but i have a low pitch for pulling multiple skiers.

 

[waterboy84]

Sounds good skidad. I leave it the way it is for now. Like i say my boat does run great.
However later on in the near future i will consider getting a 17 pitch prop and try it out. If i dont like it the no biggy ill have the old one to put back on and ill just keep either one for a spare. But ill defenently trying the 17 pitch prop and see what it does. Thanks for the info

 

[jerryjerry05]

Your comp is exactly what the book calls for.
Your motor was designed to have the top/bottom different from the 2 center holes.
Cold motor, hot motor, throttle open??? Makes NO difference.
All plugs out just makes it easier on the starter.


When asking about rpm's and pitches and speed we need to know Year, boat size, how much of a load?
And if you know how to use the trim function on the motor???

Some don't know how to use the trim.
Some think you should get max speed with 2 dogs and 4 kids and 3 fat(ugly) fishermen and 3-4 cases of beer and soda and lunch and the lunch lady.

The fuel about 1/2 tank. normal gear and 1-2 people.

Then running trimmed up see what the rpm's are.

IF??? you meet the load requirements? and the rpm's are 4800 then go down in pitch to a 17 if the original is a 19p.

I ran a 19 cause I wanted MORE!!! I got more, about 2-3 mph. and about 20-25% more fuel usage.
Needless to say I put the 17's back on and haven't looked back.

 

[tommarvin]

I thought the concept was, to get on a plane throttle back all you can to stay on a plane, to save fuel and extend the life of your motor?

 

[jerryjerry05]

Tom, the motor operates best at a certain rpm and temp.
​Running at wot will eat the fuel and going too slow will hurt it too.
​My boat operates best at 3800-4400rpm's I get about 2.2-2.4 mpg.
Going slower makes it work harder and use more fuel.
I can obtain plane and keep it there at 2500 but it's laboring and using too much fuel and going too slow.

 

[Jiggz]

Tom, you are correct if you want to save fuel. But if you want to maximize speed, then proper trimming is a very big factor. The so called sweet spot is minimal "porpoising". This is when the boat is trimmed so that it rides the water almost in parallel and bounces off the water once in a while. If the boat does not bounce off the water surface at all, then the boat is "plowing" which puts more load to the bow of the boat. The faster you try to go the more the load there is to the bow. If the boat bounces off too frequently, then it is "porpoising". Meaning more of the force from the prop is pushed downward which pushes the bow upward and losses speed. Both plowing and porpoising can reduce max rpms but is more discerned with plowing.

 

[waterboy84]

Jiggz i think you just gave sonevery great knowledge. You know everytime i went out in my boat i would leave the motor all the way down when driving the boat. That makes so much sense to tilt motor up alittle to keep the front of bow up out of the water a bit.
However the way i always drove my boat with motor all the way down and left it there. It would take up quick the bow would raise up for a second or 2 then level out and plane. Man i always hated to stop guess the back of the boat always looks like its going under water along with the wave coming behind the boat and hitting the back of the motor .
Anyhow i got use to that. It doesnt scare me anymore.
However using the trim makes sense and next time im out in my boat im gonna play around with the trim while riding around and see if that helps the rpms and speed.

 

[waterboy84]

I got a quick qestion.
On the back side of the fuel diaphram is a little hole and theres alittle hole in the motor block and then there is a gasket/seal between fuel diaphram and motor block .
Could someone explain to me the purpose of that little hole and what its for and how it works and what does it opporate. Thanks for info

 

[waterboy84]

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[waterboy84]

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[waterboy84]

Here is another pic i posted of the fuel diaphram pics. Do these looked to be strected.

 

[Nordin]

Sorry if I misunderstand you but you says there is a hole on the back side of the diapraghm? Should not be, explain better if you can.
The hole in the block where the fuelpump is mounted is for the working of the diapragm.
The pump uses the over and underpressure from the piston when it is moving up and down in the cylinder.
This makes the diaprahgm pulsing in and out and with checkvalves in the pumphousing it will pump fuel from the tank and in to the carb fuelbowl.

From your pics of the diapraghm, it looks very well.
No torn or crack.

 

[waterboy84]

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[waterboy84]

Thanks nordin. Here is a pic. The hole right above my finger. However your explaination of the hole anwsered my question.
So even with these diaphram peaces looking like they been push on and strected looks fine. Is that how there soppose to be.