Knocking noise and subsequent power loss

[northern]

If you have a heat gun check the engine and exhaust risers and rubber exhaust piping when engine is good and when you have the problem. I do not think it is a cooling problem but if the manifold temp goes up you may be getting too much fuel if lower temp you may have not enough fuel. Put mark on spots you take temperature as targets so you get same area each time. Just a though. Never tried it but others may have. Could be dumb idea.

 

[Espos4]

Could it possibly be that the B3 outdrive is overheating from low gear oil and/or lack of water flow?

Do you have a through-hull for raw water supply or is it still being drawn in through the drive?

On plane, there is very little of the drive in the water. Extended cruising on plane will increase the temperature of the oil and internals. If you use a through-Hull for raw water supply, there may not be any raw water flowing through the drive to cool it.

If so, Maybe you need a drive shower.

 

[Thornton69]

Sounds like a drive issue...you were going to check the oil.

Hopefully not too serious. Would think after multiple times that drive would be eating itself up and the windows in-between would be getting smaller. Had a 5.7 in my last jet boat that would develop a miss after running for a while under heavy load. Just a carb'd engine but it would drop a few hundred rpm and occasionally backfire in the exhaust. Changed out the cap, rotor, plugs and wires and never did it again. Hopefully not too expensive for the op.

 

[Stephen Kenna]

Sounds like a drive issue...you were going to check the oil.

pulled the boat today and drained some of the drive oil. First from the top to see if there was any metal in the upper part then the lower to try and isolate where if any damage was. Oil was blue/green in color, no burnt smell and apparently free of metal chips. The magnetized
plugs were also free of any metal debris. I did not drain all the oil, just some so tomorrow I will drain it all and check fo metal again.

 

[scoflaw]

Pull the drive and grab the input shaft and see if you have any play there

 

[Stephen Kenna]

OK, FINALLY have resolved the knocking noise. Running at 28MPH for 45 minutes it starts to knock. Opened the engine hatch and continued to run at cruising speed and engine is backfiring intermittently every few seconds. Sounded like a knock noise with lid closed but definitely backfiring. Checked fuel pressure and ran boat for 20 minutes and pressure held steady. If it aint fuel it has to be electric. Replaced ECM in distributor and ignition coil (so hot I could hardly hold it) Ran engine at cruising speed another 50-60 minutes and ran like a top.

Thanks everyone who put their thoughts and experiences into trying to resolve my problem.

 

[Stephen Kenna]

i wonder if the temp in the engine room is building up while running at higher rpm for a while and possibly affecting the electronic ignition system....or it could be an ignition coil that is starting to go bad....this could explain the engine shutting down but not the knocking sound you are hearing....

cliff

YOU NAILED IT !!!!! Thanks!!

 

[Paolo Villahermosa]

Hello Guys,
I have a 525EFI mounted on my Fearless 28' I am experiencing exactly the same issue of Stephen...
Can someone help out?
I have a video that I could share... perhaps someone has heard that noise before?