1998 Force 75 loss of power

[Rscamarochad]

Hello all:
I have a 1998 Force 75.
Just so you have a little history on the motor and me. I have previously been an auto tech. I'm fairly mechanical but not all that familiar with more complex marine issues.
When I bought this boat I redid the entire fuel system. I put a canister fuel filter, all new fuel lines, a new inline filter and rebuilt the carb.
I also did the lower unit lubricant and an entirely new water pump. I added a water pressure gauge and I have always monitored it closely as well as the tell tail. I also have a volt guage and never noticed any major fluctuations in voltage.
My current problem is that it seems to have lost power and now dies almost instantly when put into gear while in the water. The last time I took it out it ran great the whole trip and as I was headed for the ram I noticed the power drop off rapidly. I wound up having to use the trolling motor to get it on the trailer.
Ok leading up to this incident, the motor had a very minor and barely noticeable miss while cruising at moderate to WOT.
The motor was running "great" prior to the last day that I took her out and had the incident.
Frankly from what experience I have, I truly thought the motor lost compression in one or more cylinders. That's what it felt like.
Today I compression tested the motor cold. I got 120+ lbs on all 3 cylinders. So now I'm perplexed. I'm not sure what to test next? Coils? Regulator? Any help greatly appreciated.

 

[pnwboat]

Re: 1998 Force 75 loss of power

Make sure you are getting a good spark on all 3 cylinders. You can use an inline spark checker that has an adjustable gap, or just take a plug out and leave the wire attached to it and ground the plug to the engine block, crank the engine over and see what you get. You probably don't want the motor to start, so you may want to take all the plugs out. If the spark looks the same on all 3 plugs and it looks weak, you should check the stator windings. There are six magnets on the inner circumference of the flywheel. The spinning magnets interacting with the stator windings generates the voltage for the ignition system. The voltage is then routed to the CDM (coil packs). There is a trigger under the flywheel which actually fires each coil.

Start off by making sure the ground wire on the plate that the CDM (coil packs) are mounted to is making good contact between the plate itself and the engine block. Usually there is one Black wire that is attached to the plate and to the block. Make sure the ground wires (Black) going to the four pin modular plugs for each CDM is attached securely to the CDM mounting plate.

You can eliminate the regulator by disconnecting the two yellow wires going to it. If no difference, hook it back up and check the DC voltage on the red wire at about 2000 - 3000 RPM's. It should be around 14 - 14.5 volts.

To check the stator windings, disconnect the Green/White and White/Green wires at the bullet connectors that come out from the flywheel. Use an DVM meter and check across the two wires that come out from under the flywheel. You should read 500 - 700 ohms. If your reading is below or above the 500 - 700 ohm range then most likely the stator is bad.

If you have one cylinder that has no spark, or weak spark, swap the CDM from that cylinder to another cylinder. If the problem moves, then the CDM is most likely bad, or the male pin in the CDM/modular connector is bent or corroded away.

If all this checks out OK and you have good spark on all cylinders, you should check the reed valves.

Reed valves sit under the carburetors and will only allow the air fuel mixture to flow one direction into the intake. They prevent the air fuel mixture to flow back out of the intake/carburetor. There are 3 reed blocks, one for each cylinder. I assume you have one carburetor. The reed block assy. (all three) sits under the carb. You have to remove the carburetor, and the carburetor adapter plate to remove the reed valves for inspection. Look closely at the reed petals. If any are bent (not laying perfectly flat) or cracked or maybe even a piece missing, then they'll have to be replaced.

Here is a picture of the reed block assy. for your motor.



One thing I forgot to mention was your fuel pump diaphragm. When was the last time you replaced it?

 

[Rscamarochad]

Re: 1998 Force 75 loss of power

Man talk about a comprehensive reply. You're awesome man. I'm gonna look into these things you mentioned and I'll post my findings. Thank you infinitely

 

[Rscamarochad]

Re: 1998 Force 75 loss of power

Well I got her cranked up but S&W sounds like she's sucking wind. Has a real hard time staying running.