1990 Force 150hp O/B - New Boat Owner

[KBHicks88]

Hello everyone, I recently purchased my family a 1990 Bayliner Cobra 1904 with a 1990 150hp Force Outboard. I will admit that excitement kicked in when I fell in love with the boat which caused me to make the purchase before I looked any further into what I was purchasing. Now that I have the boat and was looking to take it in to the local shop to have it looked over and a tune up performed, I was informed they did not service this motor any more, along with all other shops in the area. So I have done some looking around on the forum before joining and decided that with the experience here that I can get this beauty running awesome.

I did purchase the boat lake ready, but I just do not believe I am getting everything that I am suppose to be getting out of this 150hp. When on the lake at WOT I am running around 4000 rpm which puts me roughly at 35mph. I am going to purchase a compression test gauge this weekend hopefully and see what pressures I pull there, and replace all the plugs. With this all being said, what other items need to be addressed before the season truelly gets here so that I can have then family out on the water.

I am sorry for the New-B questions, but I have tried using my masters in Google, but just have not found much information for this motor, or the boat for that matter. Thanks, and I look forward to being here and learning lots from everyone

 

[pnwboat]

I have a 1988 Cobra with a 1988 125HP motor that's been slightly modified. You should be getting more speed and RPM's than what you stated. It's a good thing to check the compression. Also look at the Propeller. You should have no more than a 19 or 21 pitch prop for a 150HP motor on that particular hull design. There should be some numbers on the prop hub.

 

[KBHicks88]

When I perform the compression test, what PSI should I be looking for? I have also seen talk on another post discussing decarbonizing? Is this necessary and how exactly is it performed, once again sorry, still trying to learn

 

[KBHicks88]

I will have to check the prop once I get back into town, I had to leave for a few days for work.

 

[pnwboat]

Compression readings are somewhat subjective and it depends on who you talk to. Generally 100PSI would be minimum. 125PSI average and 145+PSI would be factory fresh. More importantly is that the highest and lowest readings vary by no more than 10%.

Decarbonizing gets rid of carbon deposits on the tops of the pistons, cylinder heads and in the ring grooves. Excessive carbon on the pistons and cylinder head may cause pre-ignition, and in the rings grooves, it may cause the ring(s) to stick resulting in a poor seal and low compression.

It's only necessary if you have excessive carbon build up. If the motor is running as it should, you shouldn't have to do it.

 

[SkiDad]

my dad has an 88 Cobra too (different design) - 18' and force 125 - stock and it goes about 38. I would think you should hit low 40's without too much problems. I wonder if one of your cylinders is not firing - you can test for spark on all the cylinders by putting a timing light on each lead or get an inline spark tester at the auto store for 10-15 bucks. or maybe it just needs to run for a while to clean out all the junk. I'm sure you are aware, but if not, you need a 50:1 oil mixture in the gas. And you could try some mercury quickleen in the tank too.

 

[KBHicks88]

Thank you everyone for your responses. I will be checking the compression this weekend, and will let you all know what I find out on those results. I am going to also be purchasing new plugs since I am not sure the last time they have ever been changed.

SkiDad, thank you for the response. I am hoping that after little time running the motor and getting all the crud out from sitting, that it might begin to improve. I keep reminding myself at the same time that it is 26years old and at new it was advertised to run 46mph. I will take the suggestion on the quickleen though, and get that added to the tank as well.

 

[jerryjerry05]

My twin 88/85's still have the original compression.
With a GOOD gauge the readings should be about 145
Forces, unless they are carboned up should always have about that(145+/-)
I think the 90 150 still had the comp readings that the older Force/ Chryslers had.
In 91/92 after they stopped the 150 they started making motors with different comp ratios. Top and bottom were something like 160 the 2 centers were 145.

Now depending on your gauge???? Your readings should be within 5# of each other.
If all 5 are about 120 then the low reading is probably the gauge.

Any more than 10# will indicate a problem.
​If my motors don't start right away I do a comp test.