1989 johnson gt 150 wont take off

[theob]

Ive had this boat for about a month now and when we get it in the water it goes just fine up to about 1500 rpms.. when you go to take off it will die out.. sometimes it does take off and goes about 45 to 50 mph at about 4800 to 5000 rpm. extra people in the boat slows it down and sometimes wont take off. just putts at about 1400 to 1500 rpms.. seems like once it reaches 2000 rpms then it goes. Also, what should this be idling at? about 700 rpms right now. PS its on a 20' ranger bass boat.

 

[Monte1961]

Re: 1989 johnson gt 150 wont take off

700 RPMs in gear is not bad. That motor should be turning 5000 to 5500 RPMs @ wot with no problem. Get a spray bottle with fuel/oil mix. have someone fog the carb/s (spray) when it starts happening. If engine picks up, will need carb/s overhauled. A few things to mention, what are the compression numbers on each cylinder? Are plugs new and gaped? Are they the right ones? post back and let us know.

 

[theob]

Re: 1989 johnson gt 150 wont take off

Just did the carbs but havent had it back to the lake to see if it helped.. Ran like a champ in the barrel.. But who knows under load Carbs were pretty clean but did find a chunk of plastic in the bottom of one and another piece of plastic in the float arm on another. 140 miles to the lake. Just changed and gapped plugs before last trip but not sure if i got the right ones. They cross referenced them from what were in it. they were champion rj 14 yc now autolite 86. not sure of compression. would like to have it right before going back. 8 minutes to fishing spot and 45 to get back ...no fun

 

[Monte1961]

Re: 1989 johnson gt 150 wont take off

when you say overhauled? what exactly does that mean? soak or just sprayed and reassembled?Post back.

 

[theob]

Re: 1989 johnson gt 150 wont take off

soaked everything for about 15 minutes and sprayed with air 120 psi.. everything seemed to be clean and all ports and jets open.. Thanks for the input it is appriciated

 

[Monte1961]

Re: 1989 johnson gt 150 wont take off

soaking for 15 minutes wont fill the bill. Minimum 24hrs. Were core/welch plugs taken out? Can't get a through cleaning without doing this. I would take carb/s back off and redo! But that's just me! Maybe someone else will chime in with there experience! Good luck.

 

[theob]

Re: 1989 johnson gt 150 wont take off

Carbs had no varnish or any kind of build up. Actually looked they had been cleaned recently. Replaced gaskets and needle valves. I dont have access to previous owner. It had champion plugs in it and replaced with autolite. What is the best plug to use? I dont mind paying a little extra to get something that will perform/last better

 

[Monte1961]

Re: 1989 johnson gt 150 wont take off

SPARK PLUG, CHAMPION QL77JCR. RADIO NOISE SUPPRESSION PLUG (6 required per assembly)

 

[theob]

Re: 1989 johnson gt 150 wont take off

Ok thanks for all the input