93 johnson 115, Tac reading wrong?

[MOETOROLA]

I have a Nitro 170DC, with a 93 johnson 115 running a 13x19 aluminum prop. The problem is a mechanic told me that somethin is wrong with it.<br />At full throttle and trimmed out(accordind to the trim indicator) The motor is only turning 4200rpm @ about 40mph. He told me that turning that low of an rpm could damage it, and needs to be checked. Enging takes 5 tries to get started after 20 min of not running. Another ? how fast should this boat run with this motor typically, ive heard 40 and 65, what is the right answer?

 

[Basscat 1]

Re: 93 johnson 115, Tac reading wrong?

The mechanic is correct, that boat should be turning at least 5800 rpms at wot, or it could damage the engine. Im not sure about your speed of your boat, to many factors to consider.<br />If the engine has been shut off for only 20 minutes it should start back up. I would have the engine checked out, or it could end up costing you a lot of money in the long run.

 

[MOETOROLA]

Re: 93 johnson 115, Tac reading wrong?

Update, Was checking out the engine and noticed something. The roller rubber was missing on the timing advance arm ( not sure what exactly it is called) I temp installed and cut a piece of hose to take up the slack of the roller. It seemed to make a diference, "as far as the engine sounded". I will see how she does down at table rock this weekend. Any one know the part name and number so i can order one?

 

[MOETOROLA]

Re: 93 johnson 115, Tac reading wrong?

Update, Took the boat out, and had no change with roller. so back to square one. Still runnin 4200 at 42mph. Could timming be off? Any body ever ran into this on this motor. When you have been running the motor and its warmed up. And restart it after say 20 or 30 minutes, it makes a couple of puff sounds like its breathing back on itself. or maybe a backfire.

 

[CATransplant]

Re: 93 johnson 115, Tac reading wrong?

Something's sure wrong with that engine. Time for a complete diagnostic and tune-up there. This could be a lot of things, so you'll need to start with the standard tests. <br /><br />Compression<br />Ignition<br />Carburetion<br /><br />You need a factory service manual to do the diagnostics properly.<br /><br />Best of luck with your outboard.

 

[Basscat 1]

Re: 93 johnson 115, Tac reading wrong?

Also take a look at your reeds.

 

[Steve135]

Re: 93 johnson 115, Tac reading wrong?

Check to see if the fuel pump is connected to the crankcase side of the engine. Or if there is a hole in that line. This would cause lack of fuel pressure from getting to the carbs. And just a little sign of leaking fuel. Just had that one on a 150 cross flow that beat me up. Hard starting from just perfect running one week to the next and low rpms as well. Not sure what this does to an engine at WOT with lack of fuel? But I am thinking it wasn't good cause it was getting all the air it wanted???

 

[MOETOROLA]

Re: 93 johnson 115, Tac reading wrong?

Thanks Basscat, Ill check for a leak. There is a slight bit of residue under the lines on the fuel filter side. Although it does not smell of fuel very bad when i pull of the lid. <br /><br />Another thing, the spark plug cables dont look to be in all that great of shape. had the engine idling and pulled the plug cables one bye one. 3 of the 4 cables i could hear jumping insulation but one of them did not. Could this be a sign. I did hear a change in the engine idle when i pulled the non arcing plug wire though, as well with the other 3 too.