1988 90 hp Johnson- Perplexing performance puzzle

[waynehol]

OK im pretty new to outboards and am having an issue.
On a 16ft 1980 Cobia CC tri hull, running in salt water.
For the most part it runs great and strong.

However, when we pull a tube after a while, we get severe RPM drop. Throttle up does nothing. Last time I squeezed bulb during the episode but it made no difference. I pulled throttle to stop and it died. Restarted, ran fine.

My suspicion is that it has something to do with water washing into the back of the motor. It seems like after tubing, turning, stopping and starting a lot is when it does it,. Is there somewhere in the back of the motor (the upper exaust?) that water could backwash into to make this happen>

Some more info, Here;s what I have done to the motor recently.
1) Clean and rebuild carbs
2) new plugs and wires
3) new water pump
4) inspected fule filter (clean)


Thanks for the help.

 

[tashasdaddy]

Re: 1988 90 hp Johnson- Perplexing performance puzzle

actually sounds like it is starting to run hot at that point. i don't believe the 1988 had "slow" on it. i would investigate with an infrared thermo. also test you over heat alarm sender.

 

[waynehol]

Re: 1988 90 hp Johnson- Perplexing performance puzzle

Hmm thats something I havent thought about. I dont have an infra red thermometer.Will see if I can borrow one.
I was looking around at the temp sending unit and noticed it is not connected,. THere is a brown wire off each temp sensor and they are not connected, I will have to see how to connect this back,

Thanks for your input!

 

[tashasdaddy]

Re: 1988 90 hp Johnson- Perplexing performance puzzle

i use this one. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93983

 

[CharlieB]

Re: 1988 90 hp Johnson- Perplexing performance puzzle

It is possible that the additional load of pulling that tube, even tho not at WOT, may be more work for the motor, lugging/loading the motor just enough more to causing a temp rise, nearing overheat/siezure.

You didn't tell use your WOT RPM with and without the tube, it may not be safe for the tubee to find out what it is with a tube.

Many boaters carry a second prop of a little less pitch for use on those outings to tow skiers and tubes. Just be sure to keep an eye on your tach when NOT towing.

 

[waynehol]

Re: 1988 90 hp Johnson- Perplexing performance puzzle

Thanks Charlie. That is good info. I wil get back with the tach specs as soon as I check it out.