engine knocking and loosing power

[crookedmullet]

I just got a call from a friend of mine that is on the water. He's got a 1993 90-hp Mariner. As soon as he started the engine this morning, he noticed a knocking going on, the engine idled fine so he decided to go with it. After he left the no wake zone, he put it into full throttle and worked fine until about a 1/2 mile when it lost power and went into idle speed. He decided to leave the throttle opened and after a few minutes the engine revved up again and ran fine for about another 1/2 mile and then lost power again. During this whole time, the engine was making weird knocking sounds. <br />This is the description he gave me. I figured I could run it across this forum and get some ideas from the experts to try and save him some cash.<br />I had him check the fuel/water separator and there is no signs of water. Even when the engine lost power, the primer bulb stayed hard.

 

[Texasmark]

Re: engine knocking and loosing power

My experinece with knocking on 2 cycles is when one cylinder doesn't fire every time. Reason could be fuel or ignition.<br /><br />Need some more info to separate the two. History of his rig to understand if varnish is clogging up his carbs but this doesn't sound like varnish or a stopped up fuel system.....too repetitive.<br /><br />On ignition systems, if you have an overheat condition on the solid state switch it will quit switching. Firing times per second are 1/6 at idle what they are at full throttle. <br /><br />What I may be hearing is that his power pack(s) get hot, quit switching all cylinders, rpms drop, whatever that got hot and quit working cooled down enough to start working again, and on and on.<br /><br />One thing to check is if this engine has a solidstate trigger module or 3 of them or whatever, they are mounted to something. This something is a heat sink and sinks the heat from the electronics inside. <br /><br />There is usually a white gooey thermal compound installed between the two at the time of assembly to help insure the heat transfer. Over time this can degrade and cause thermal problems. Solution is to remove the power pack from the engine, clean off all the old white thermal grease, and with some Radioshack Thermal Grease, grease her up again. When you bolt it back on you should see it squish out. If not, put in more till it does.....just enough to see that you got full coverage.<br /><br />Mark

 

[crookedmullet]

Re: engine knocking and loosing power

Thanks for the reply Mark. I will check that out. First chance I'll get to look at it will be Tuesday morning. I'll let you know what I find.

 

[gatorred]

Re: engine knocking and loosing power

try coil pack get hot cyl cut's out

 

[Rabbitdawghunter]

Re: engine knocking and loosing power

I believe I would do a compression test first before I got off on the ignition issues.

 

[Boatwizard]

Re: engine knocking and loosing power

Second what Rabbit said.

 

[andy6374]

Re: engine knocking and loosing power

Drop the L/U and see if the sound persists. Take the compression test.<br /><br />Hopefully he didn't cause major (extra) damage by running the thing that long.