Loss of power & clacking

[nabeel.alsalam]

I was in a sailboat regatta last weekend and I lent my boat to the race committee to use as a rescue boat. <br /><br />While they had it two things happened to my 1991 Johnson 40 hp engine. <br /><br />First, while on a plane it suddenly lost most of its power and would only run at a 1800-2000 rpm with WOT. It idles OK although a bit slower than it was before (750 vs. 1000 rpm in neutral). <br /><br />Second, the engine is now making a mild and steady clacking sound that wasn't there before. <br /><br />From searching previous posts on this forum, the most likely reason for sudden loss of power seems to be crude clogging the high speed orifice or passages. Correct? So although I'm surprised stuff can get past the in-line OMC filter (which I admit I have not changed recently) and althouggh I just rebuilt the carbs a few weeks ago, I guess I'll at least try removing the drain plug from the two carbs and the main jet orifice behind each. <br /><br />Any thoughts on what might have happened and what I might do to narrow down the possibilities? Thanks.

 

[DJ]

Re: Loss of power & clacking

It sounds as if you lost one of your two cylinders.<br /><br />Do a compression test. That will verify your situation.

 

[CATransplant]

Re: Loss of power & clacking

The clacking sound doesn't seem like it comes from a faulty carburetor to me. I'd suspect that one cylinder has some damage internally instead.<br /><br />Idle it on the muffs, if you can, and pull one plug wire at a time. Betcha one cylinder's plug won't make a difference. I'll also bet a compression test will give you more news you won't like.<br /><br />Bummer.

 

[nabeel.alsalam]

Re: Loss of power & clacking

OK. I'll do a compression test first. <br /><br />By the way, what does "loss of cylinder" mean? A crack, a hole, ...

 

[CATransplant]

Re: Loss of power & clacking

A number of things can cause loss of a cylinder, which just means that it's not firing, turning your motor into a single-cylinder one. It could be an ignition problem, but that wouldn't cause a clacking sound.<br /><br />It could be a holed piston, which will result in virtually zero compression on that cylinder. Could be a broken ring, which would result in much lower than normal compression.<br /><br />If the engine was running right before this happened, then very low compression on one cylinder is going to lead to pulling the head for a visual inspection.<br /><br />I doubt you're going to enjoy this...sorry.<br /><br />Nota Bene: I don't loan my boat to anyone. I did once. The guy ran out of gas and filled the tank with plain gasoline. No oil. He took it back out and destroyed a nice 9.9 horse engine.

 

[fireman57]

Re: Loss of power & clacking

As someone said on another forum on this site:<br />"Never loan your wife or your boat. You'll get them both back with a rod thrown in them."

 

[nabeel.alsalam]

Re: Loss of power & clacking

I just checked the compression. The top cylinder is 110 and the bottom is 125. (I cranked about 1 second). Is that an acceptable variation?<br /><br />While doing this I notice the plugs are very different looking. Do they provide a clue? <br />

 

[jfm1]

Re: Loss of power & clacking

compression seems to be within 15% looks like you lost spark

 

[Walker]

Re: Loss of power & clacking

I'd say the plug on the left was running in a very lean cylinder.

 

[nabeel.alsalam]

Re: Loss of power & clacking

I just tested the spark quality using a home-made gizmo to see whether it will jump 7/16". It does. <br /><br />Does this narrow it down to a fuel problem? <br /><br />By the way, if one carb doesn't supply fuel and the operator continues to run the motor will the cylinder with a bad carb get lubrication?

 

[Goldfish]

Re: Loss of power & clacking

nope, fuel has the lube in it, so no fuel = no oil = a very angry piston, and you know what happens when pistons get all hot and bothered...

 

[fireman57]

Re: Loss of power & clacking

Hard to tell but the gap looks small. Is the spark bright blue and snaps real loud? If it's orange or yellow it won't fire the plug.