Low RPM / Loss Of Power - Diagnosis Help

[AguaSki]

Boat was running great until the end of the day. The channel of the lake I was in had a layer of saw dust looking stuff floating on the water. While cruising, after leaving the saw dust area, I noticed that my water pressure was about 4-5 psi when it is normally 10 psi. About the time I noticed the water pressure change, I entered a “no wake” area so I eased off the throttle. Then I noticed my motor was not running well. I turned off the engine and looked around, but did not find anything. The motor fired back up, but was still running poorly. I turned around and got out of the “no wake” area and hit the throttle, but I could not get above 2,500 RPM. Fortunately my bro. in-law was with me and towed me back to the ramp.

When I got home I tested compression. Still 120 psi on all 4 cylinders. I started reading my Clymer’s manual and learned about a S.L.O.W. circuit that is activated when engine temps reach 203 degrees. Once activated the engine cannot exceed approximately 2,500 RPM. The S.L.O.W. circuit is deactivated when the engine temp is below 162 degrees and the engine is restarted. In my case, I never tried restarting and let my bro. in-law drag me in.

My theory is that this saw dust stuff ruined my impeller. The damaged impeller caused my engine to get too hot and activated the S.L.O.W. circuit, which is the reason I could not rev to higher RPM’s. Does this make sense? The fix is a new impeller?

Additional information:
• I am really new to outboards and not that mechanical in the first place.
• 1978 Johnson V4, 140 hp. Can't tell for sure from my manual if my exact engine is equiped with the S.L.O.W. circuit, but I believe it is.
• 1978 Glastron SSV-188
• No temperature gauge, but I do have a water pressure gauge
• Never heard the overheat alarm, and I tested it to be sure it works.

Please offer your thoughts on the diagnosis, and remedy.

 

[Javelin 353]

Re: Low RPM / Loss Of Power - Diagnosis Help

Check for spark on all cylinders
you should be able to hold your hand on the cylinder heads for several seconds before they start to burn.
Make sure impellers is pumpimg water
Was this saw dust stuff thick in the water ??

 

[dick reaves]

Re: Low RPM / Loss Of Power - Diagnosis Help

I have the same engine except 1977 and also noticed the low RPM when the engine overheated. Thanks for the heads up on a S.L.O.W. circuit. You can check my post on the overheating problem I'm having on one side of the engine. Wonder if the age of the engines/cooling pump is the problem? Good luck!

 

[clint]

Low RPM / Loss Of Power - Diagnosis Help

Sounds like no spark in one cylinder at 2500 rpm's. Check all wires and plugs. Run engine and feel around cylinder jackets for the cool cylinder not firing. Maybe a spark plug.
Clint 8)

 

[Walker]

Re: Low RPM / Loss Of Power - Diagnosis Help

Neither of your motors has the SLOW system.

 

[AguaSki]

Re: Low RPM / Loss Of Power - Diagnosis Help

Maybe it is the top cylinder on the port side. A few months back while testing compression the metal piece inside the rubber boot that grabs the top of the spark plug came out. There is now a sharp point from this piece of metal sticking out the side of the boot. Since everything ran fine, I just wrapped the boot up in electrical tape and kept going to the lake. A new set of wires, especially on the cylinder in question may be in order.

This still does not explaine the loss of water pressure, but I am guessing that is because of my low RPM situation.

Anymore thoughts/guesses?

 

[clint]

Re: Low RPM / Loss Of Power - Diagnosis Help

Replace the wires,,I had a simular issue with plug wire boot shorting out the left #4 port side cylinder and it was grounding out to the engine cover because wires were old & porous. Engine ran great on muffs but every time I put cover on it would be so close to the boot. When I ran boat in water it wouldnt plane out. I couldnt get it over 2500 rpms because of the #4 wire shorting out. Yes, new wires $20.00 is your remedy. Sounds like your water pressure problem was due to low idle, rpm. Happy Cruising!
Clint 8)

 

[AguaSki]

Re: Low RPM / Loss Of Power - Diagnosis Help

Can plug wires be purchased or do you have to buy all the pieces and make them?

My local West Marine is telling me that because of the age of the motor I need to make my own wires. Any thoughts? This is a crossflow that should not have changed that much through the years.

Also, does anyone else have an opinion on my issue and things I should be looking into?

 

[F_R]

Re: Low RPM / Loss Of Power - Diagnosis Help

Not so sure the wires come out of the coils do they? The rubber boots and spring thingys are replaceable. Parts list at http://epc.brp.com/default.aspx?brands=ej&lang=E

 

[clint]

Low RPM / Loss Of Power - Diagnosis Help

The wires are imbedded in the coil. You would actually have to buy a new coil or coils. Good Luck!
Clint 8)

 

[AguaSki]

Re: Low RPM / Loss Of Power - Diagnosis Help

I made new plug wires and replaced the spark plugs. I am still seeing the same symptoms. I can't get much past 2,300 RPM. All 4 cylinders are hot. Any additional thoughts on what I should be looking for?

I do have a good repair shop near by, but they don't work for free. If possible, I would like to work this out myself to save some cash.

 

[wilde1j]

Re: Low RPM / Loss Of Power - Diagnosis Help

Pull the LU and check for blockage by forcing water or air up the waterpump discharge tube. I assume the water pressure has stayed low. Have you checked to see if the engine is overheating (can you put your fingers on the head or sides of the block while running? It should be ~ 140 to 150° F ... pretty warm to the touch, but not really hot.

While you have the LU off, check the water pump condition (waer plate grooving, liner wear, impeller condtion, etc.

 

[clint]

Low RPM / Loss Of Power - Diagnosis Help

You must has sucked the Debris into the water pump housing and pickup tube probably is partially blocked also. Drop the Lower unit and get to the source. Hopefully it didnt get into thermostat housing blocking flow to the thermostats. If you have a compressor I would try that first since it is sawdust it will just blow out and break up easier rather than with water which will make a bigger more solid clog. Keep your cowel cover on when blowing it out with air not to get any into your intake manifold. Good Luck!
Clint