Force 125 🙃🙃🙃

[Racinfreak25]

Hello all,
I'm pulling my hair out on this one. I have an 88 force 125. Received the boat and engine for free from my uncle. The boat had been sitting for 6+ years. So I drained all the fuel. Cleaned the carbs(surprisingly clean for sitting). And went on my first sea test. She ran great got up to about 40 mph and planed beautiful. Until the fuel filter plugged up(my fault for not changing it). So I change that and go to another lake with Hope's of a nice family weekend on the water. No beans! Acted very boggy and wouldn't do much over 20mph. So at the direction of others I do a compression test. 1- 170 2-170 3-170 4-105..... okay so problem solved ended up having a stuck ring. New set of rings and bam. Well now it appears #4 cylinder isn't "sucking fuel" into the chamber. Almost a perfectly clean plug when removed. I've swapped reeds for the upper bank. Compression is even at 170 now across the board. Carbs are spotless. I'm at a loss. Cylinder walls still had cross hatching and no scoring. What would cause that cylinder alone to not "suck fuel" with good compression.
thanks
Joe

 

[schematic]

broken or missing crankshaft sealing rings? They look like a small piston ring...

 

[Racinfreak25]

broken or missing crankshaft sealing rings? They look like a small piston ring...

I had the case split and they all appeared to be in great condition. Free moving I had the same issue prior to finding low compression and thought the rings were culprit. The last thing I want to try is swapping carbs and all brackets. Then if that isn't it possibly the port cover? I'm unsure on these multiple cylinder engines if they use the same side of the engine for intake and exhaust or if they are split like a smaller 2 stroke.

 

[Nordin]

Check the intake port cover, maybe the gasket is leaking.
They have intake ports at one side and the exhaust at the other side.

 

[jerryjerry05]

If your comp is good then your probably getting fuel.
You CAN'T draw fuel into 1/2 of the system.

Just sounds like it's not firing on that cyl.??
Get a spark checker(Auto Zone) and measure the spark.

Port cover test or starting fluid test.
Can of SF, start motor and spray the SF all around the intake side, base of the carbs, under the coils
and under the packs.
If that makes the motor run differently? stutter, backfire, miss, stall?? Then
your sucking air.

A small backfire, even a cough can blow the port cover gaskets.

 

[Racinfreak25]

Well guys, problem solved.... the fuel pump diaphragm had ripped on the #4 cyl pulser. Dumping loads of fuel and essentially washing the cylinder clean. Lack of air wasnt allowing it to fire. Lucky it didn't hydro lock on me. Found it by accident while inspecting the intake port gaskets. Attached a 2.5-6 psi electric fuel pump and she runs like a champs on all cylinders.... hitting the water tomorrow to finish up the break in of the new piston rings. Thank you everyone for chiming in this was definitely a first for me after working on these things for years.

 

[jerryjerry05]

Adding an electric fuel pump is like adding a bomb.
Fix the old.

 

[Racinfreak25]

Adding an electric fuel pump is like adding a bomb.
Fix the old.

May I ask why you say it's like adding a bomb? We run stock car and run these electric pumps reliably every week. We are weeknight and occasional boaters maybe 30hrs a year.

 

[foodfisher]

Two cycles draw fuel as required. An elec. pump force feeds fuel through the lines. Loose connections, cracked lines, faulty needle and seat, other possible leak points lead to fuel and fume buildup. Boom

 

[jerryjerry05]

Yup, what he said.

 

[Racinfreak25]

Two cycles draw fuel as required. An elec. pump force feeds fuel through the lines. Loose connections, cracked lines, faulty needle and seat, other possible leak points lead to fuel and fume buildup. Boom

That's the assumption I made after reading the original comment. Well we took the boat out last night and she runs like a top. After breaking the new rings in she got up in plane and cruised. Fuel pump kit will be here today or Tomorrow. Had a few (small marine screen type) filters plug while running. Have a new fuel filter and water separator unit at the local marina waiting for me. Thank you again guys!