1988 125hp Force lower unit woes

[Sandy-man]

Well, something tells me my #3 cylinder needs a ring job. Compression test results as follows:
#1 - 90lbs
#2 - 89 lbs
#3 - 72 lbs
#4 - 88 lbs

Not sure of the accuracy of my cheap compression tester but pretty sure the big difference indicates a problem.

 

[Sandy-man]

On the brighter side, however, I sprayed starting fluid into the throat of both carbs and she starts right up. Before spraying all she would do is turn over. I'm now waiting for my personal assistant, aka wife, to get home so I can run the starting fluid test around the port gasket.

 

[Jiggz]

If it started with starting fluid, I'm assuming this a mix of fuel and oil from your tank, then it indicates there is fuel delivery problem or carburetion problem. If you have a clear fuel filter between the fuel pump and carb inlet, is it full of fuel when starting? I mean right after you depressed the primer bulb and getting firm.

It it is full, then you need to check the carbs' bowl. If you don't want to dismount the bowls, just tilt the motor all the way up and continue to depressed the primer bulb and you should start seeing fuel coming out of the carb's mouth. This tells you the carb bowls are full.

If you don't have the clear fuel filter, highly recommend you install one. Even a cheapo Fram G2 (less than $5 at Wally mart and even comes with hose clamps) it is indispensable for fuel related troubleshooting.

 

[Sandy-man]

There is no fuel filter between the carbs and fuel pump, but there will be one soon. It sure purred like a kitten for a couple seconds running on the aerosol starting fluid, sounded real good. I have a few more tests to run, one is to see if it's sucking air through the port gasket.

Would like to see what people think about the difference in compression between cylinder 3 and the other 3 cylinders. Is it significant enough to pose a real problem?

 

[Jiggz]

If this compression reading is on other cylinders besides #3, it would be a serious concern. I say this because on this motor, the fuel pump is mounted on the #3 cylinder and a simple torn fuel pump diaphragm can affect the compression number slightly.

And since you are having fuel delivery problem, (which you should confirm with a clear fuel filter) or carburetion, it's also smart to check the fuel diaphragm as part of your troubleshooting!

 

[Sandy-man]

If this compression reading is on other cylinders besides #3, it would be a serious concern. I say this because on this motor, the fuel pump is mounted on the #3 cylinder and a simple torn fuel pump diaphragm can affect the compression number slightly.

And since you are having fuel delivery problem, (which you should confirm with a clear fuel filter) or carburetion, it's also smart to check the fuel diaphragm as part of your troubleshooting!

Music to my ears, thank you! What's the chances of taking the carb bowls off without having to replace the gaskets? I can do this on my 72 Yamaha motorcycle. Are the carbs on this motor as adversely affected by water and small particles as my mikuni carbs?

 

[Jiggz]

Usually, there's no need to replace the gaskets as it usually stays up there in the body. Just be careful with the bottom screw as this is also the main jet and made of brass that can easily be destroyed. Personally, I'll start with the fuel pump first and installing a clear fuel filter. And then continue troubleshooting from there.

 

[jerryjerry05]

The pump being on #3 shouldn't have any bearing on the compression readings.
It's 17-18# difference that's about 20% and 20% isn't acceptable at all.

The port cover gasket being bad(?) won't have a bearing on the comp either.
Remove the port cover and inspect the rings for carbon, missing pieces.
It could be a head gasket?
Had a miss on my port motor, comp was 145 all 3
Pulled the head and there was a tiny hole about the size of a pencil lead.

I bought a camera for my cell phone, it has a light on the end and the pictures really good, about 10$
Or remove the plug and use a coat hangar wire and feel for scoring on the cyl. walls?

The effect of tiny particles in your carb: was working on a 120 with a miss. Everything tested good, comp, spark etc.
Cleaned the carb 3X swapped the carb with a carb from his other 120 (twin motors) the miss followed the carb.
The 4th time I cleaned it(never did see anything??) the miss went away. I'm guessing a tiny piece of dirt the size of a pin head got stuck and was causing the problem.

I use a Fram G-2 G-3 or G-12 any of these catch the fine stuff that can go through the pump.

 

[Sandy-man]

The pump being on #3 shouldn't have any bearing on the compression readings.
It's 17-18# difference that's about 20% and 20% isn't acceptable at all.

The port cover gasket being bad(?) won't have a bearing on the comp either.
Remove the port cover and inspect the rings for carbon, missing pieces.
It could be a head gasket?
Had a miss on my port motor, comp was 145 all 3
Pulled the head and there was a tiny hole about the size of a pencil lead.

I bought a camera for my cell phone, it has a light on the end and the pictures really good, about 10$
Or remove the plug and use a coat hangar wire and feel for scoring on the cyl. walls?

The effect of tiny particles in your carb: was working on a 120 with a miss. Everything tested good, comp, spark etc.
Cleaned the carb 3X swapped the carb with a carb from his other 120 (twin motors) the miss followed the carb.
The 4th time I cleaned it(never did see anything??) the miss went away. I'm guessing a tiny piece of dirt the size of a pin head got stuck and was causing the problem.

I use a Fram G-2 G-3 or G-12 any of these catch the fine stuff that can go through the pump.

So you're saying it's either a blown head gasket, scored cylinder wall or a bad compression ring. In either case I will have to pull the head. Unless I miss my guess, approximately 90 lbs in the other 3 cylinders is pretty low, guessing this because your motor had 145. Unless of course my cheap brand compression tester is inaccurate by a long shot. If this is the case then I should probably plan on honing all cylinder walls and probably new rings in all cylinders. Darn, I really didn't want to have to go this deep, but it would be a lot cheaper than replacing the motor with another used motor of unknown possible problems. Boats, the rich man's toys, or so it seems.

 

[Jiggz]

Inspect the fuel pump diaphragm and if it's good then do another compression test. This time make sure you squirt a few fuel oil mix into each cylinder. And that all plugs are removed. However, if the fuel pump diaphragm is torn, replace it and then do another compression test. Again, make sure you squirt some fuel oil mix into each cylinder before each cylinder test Post your results..

 

[jerryjerry05]

Your low readings? your economy gauge is probably the reason, or the way you did the test?
Remove all the plugs?
Ground the wires, install the gauge, turn the motor, let it turn until the gauge stops going up.

The introduction of oil into the cyl.
That seals any possible small areas that can loose air.
If it's a bad leak? the oil shouldn't make much difference.

Harbor Freight tools: some are ok, lots aren't.
I paid 160$ in 86/7 for my tester and it gives the same results today as it did then.
Get another gauge and try again.

 

[Sandy-man]

I always have doubts pulling something apart without replacing all seals and gaskets when putting back together. So I just ordered a new diaphragm, all gaskets and screen for fuel pump and #3 port cover.

I did another comp test based on your recommendations and saw approx 8-9 lb improvement in all 4 cylinders. So there is still approx 20% difference between #3 and other cylinders.

Performed the starting fluid test again around all 4 ports and found no leaks around them. Sprayed starting fluid into the throat of both carbs again and again got a very smooth 2 second running motor. Tried to start again without spray and got a cough and backfire.

While waiting for the parts to arrive I will pull both carb bowls and clean them very thoroughly and install a Fram fuel filter between carbs and pump. Once I get the parts I will rebuild the pump and perform another comp test and report back. It will be a week or so before I get all done.

 

[jerryjerry05]

Check for water?

 

[Sandy-man]

Check for water?

I will do this when I drain the carb bowls, drain into a clear plastic container and let it settle for a while.

 

[jerryjerry05]

Tilt the boats nose up as far as the jack(??) can lift.
Then let settle for 15-20min.
Then unhook the gas line at the fuel pump.
Squeezie the gas into a clear glass jug try to get at least 1-2 quarts.

Then let settle.

Sometimes the boat sets and the water in the tank goes to the front and only gets sucked up when it's used
in the water??

 

[Sandy-man]

Received my fuel pump gaskets and diaphragm Friday and finally got a chance to remove the pump and port cover. Positioned the piston at BDC, shined a light into the cylinder from the port and took this picture from the spark plug hole. That's the bottom of the cylinder, the top and sides look smooth. Looks like a ring job and cylinder honing is in order.

 

[Sandy-man]

Now I'm into rebuild of the fuel pump and the diaphragm is torn very badly. Before I put it back together I need to know if I should use any silicone sealant on the gasket.

 

[Sandy-man]

Tilt the boats nose up as far as the jack(??) can lift.
Then let settle for 15-20min.
Then unhook the gas line at the fuel pump.
Squeezie the gas into a clear glass jug try to get at least 1-2 quarts.

Then let settle.

Sometimes the boat sets and the water in the tank goes to the front and only gets sucked up when it's used
in the water??

Please see my other 2 posts. Silicone on fuel pump gasket?

 

[Jiggz]

Now I'm into rebuild of the fuel pump and the diaphragm is torn very badly. Before I put it back together I need to know if I should use any silicone sealant on the gasket.

No need for silicone. The diaphragm should seal properly using cross torque method.

 

[jerryjerry05]

No silicone, but the cyl. needs work (
Time to start a rebuild thread.