1988 Force 125 HP Compression Test

[oavila88]

Just purchased a bayliner 1900 with an outboard Force 125 HP. Took it out to the lake and it with two adults it got up to 35 MPH. When we had 5 people and tried to pull a tube it would only go 10 MPH. Tried to do a compression test and the reading on all 4 cylinders was around 60 PSI each. The boat has a 13 pitch.

Does that sound right - 60 PSI? I was expecting to get a reading of around 120 psi.

Thanks.

 

[bigred69]

Re: 1988 Force 125 HP Compression Test

With those reading the motor is in need of a rebuild. Should be 130 to 120.

 

[jerryjerry05]

Re: 1988 Force 125 HP Compression Test

Those reading?? Probably a different tester??
It probabably woudn't start if all had 60#
Remove all the plugs??Throttle open?
Turn it over at least 6 times or until it stops going up.
Make sure you ground out the plugs or use a jump box.


Do it again and get a different guage.
Profile,location?You might be close to someone who can help.J

 

[bigred69]

Re: 1988 Force 125 HP Compression Test

Sorry forgot an s .

 

[foodfisher]

Re: 1988 Force 125 HP Compression Test

35mph with two adults is right on. Not indicative of 60# compression. 10 mph w/5 adults and a tube is a bit overexagerated(sp), yes? Still that's quite a load and won't get close to running with only two adults. Probably not even on plane.

 

[Jiggz]

Re: 1988 Force 125 HP Compression Test

I believe either the compression gauge is screwed up or maybe of the press and hold type instead of the screw-in type was used. To be able to get 35MPH with two adults, even with a single adult, you would have to have at least a decent compression of 110PSI across. The 13" pitch is quite undersized for a 125HP unless you are referring to the diameter of the propeller. The standard prop is 13 1/4"-17P and can easily handle a 13 1/4"-19P. With 5 adults you need to make sure you trim up a little to raise the bow otherwise you could be "plowing" real hard into the water.

 

[oavila88]

Re: 1988 Force 125 HP Compression Test

Thank you all for your responses. The compression tester was bad. I got another tester that shows 115,110, 115, 110 compression which make a lot more sense. I will be changing the propeller to a 15 pitch and see how it goes.

 

[JB]

Re: 1988 Force 125 HP Compression Test

Thank you all for your responses. The compression tester was bad. I got another tester that shows 115,110, 115, 110 compression which make a lot more sense. I will be changing the propeller to a 15 pitch and see how it goes.

I think you are going the wrong way, oavila. I think you are already overpropped for such a heavy load with the 13". I would try an 11" or just not load the boat so heavy. You really need a tach to properly evaluate what is going on.

Check out our Props Forum and see what advice you can get there. My guess is that a shorter prop will be recommended.

 

[emoney]

Re: 1988 Force 125 HP Compression Test

How big are the 5 adults? Often times we overlook (or people under-exaggerate) the poundage. 5 people that weight 150lbs each is a lot different than 5 that average 250. I hope they're all chipping in with gas money at least, lol.

 

[Jiggz]

Re: 1988 Force 125 HP Compression Test

Thank you all for your responses. The compression tester was bad. I got another tester that shows 115,110, 115, 110 compression which make a lot more sense. I will be changing the propeller to a 15 pitch and see how it goes.

The decision on which size of prop you will need depends on the performance of the engine based on RPM. With a standard prop of 13 1/4"-17P the WOT RPM is supposed to be between 5000-5200 RPM. Your current prop is 13P and with 5 people you said it would not go above 10 MPH, but what was the engine RPM at WOT? If the WOT rpm did not go above 4000 then you will need to reduce prop pitch. But if the WOT RPM was still above 4500 RPM, then you will need to increase prop pitch.

 

[oavila88]

Re: 1988 Force 125 HP Compression Test

The 5 adults combined weight of 700 lbs.

My boat does not have a tach. So how do I go about measuring WOT RPM?

 

[jerryjerry05]

Re: 1988 Force 125 HP Compression Test

They sell an item called a Tiny Tach.
It works great.
Just get one for the outboard you have.

Where did you get the pitch#s??
Look real close at the prop and see if you can find any other #s.
That boat new came with a 19c or 17c
Profile??Location?
You might be close to someone who can help.

 

[foodfisher]

Re: 1988 Force 125 HP Compression Test

Car analogy-High pitched prop with a load is like jumping off the line in third gear. Ain't gonna happen. Lower pitched prop will get you off the line with a load, but won't break any speed records. Pitch the prop according to what you want to do, go fast or pull loads. Warning, props are easy to change but they cost a lot of gas money.

 

[jerryjerry05]

Re: 1988 Force 125 HP Compression Test

Like food says the wrong prop can cost a bunch in gas$$$
I have a 21 with twin 85's I wanted more speed so I changed props from a 17 to a 19.
I got more speed about 3-4mph.
But the gas consumption went up about 20-25%