1989 johnson 150 gt help

[jrc27]

just bought a new boat with a johnson gt 150. the boat has not been run in about 16 months. had it out for first time today to test it out.. changed lower unit oil before hand.. sem to miss a bit and only hits speed of 42 mph at 5000 rpm.. what can/should i do to it... (change plugs, use some sort of engine tune up??) need help

 

[Jack Shellac]

Re: 1989 johnson 150 gt help

I believe I'd do it in this order: 1. Decarb and new plugs 2. New plug wires 3. Carburetor rebuild. Check motor out between steps to see if problem clears up. If the basics don't fix it, it's time to go further with compression tests, etc.<br />This is after making sure all electrical connections are clean and tight before anything else.

 

[jrc27]

Re: 1989 johnson 150 gt help

what do you do exactly to decarb? someone told me something about omc tune up spray or something to that effect, als something about carbon. would these fixes have anything to do with helping speed.. or just the part of feeling like it is missing

 

[jrc27]

Re: 1989 johnson 150 gt help

what kind of plugs do you recomend

 

[jrc27]

Re: 1989 johnson 150 gt help

what kind of performance gain would i get from rebuilding the carbs.. could this be a solution to my earlier post? also what would it typically cost for a carb rebuild?

 

[jrc27]

Re: 1989 johnson 150 gt help

can anyone tell me if this might be fuel related?

 

[dkondelik]

Re: 1989 johnson 150 gt help

'afternoon jrc27,<br /><br />wow, lots of questions.<br />yup, carbs can cause lots of problems,... as can carbon build up.<br /><br />do a search on this forum for "decarb". there is already a wealth of info on the subject.<br /><br />run a compression test before and after a decarb treatment. results will let you know if you've got a "sound" motor to work with.<br /><br />if the results are ok, then remove and service carborators. STRONGY suggest you get a service manual if you don't already have one. aftermarket manuals are available at the link at the lower left corner of this page.<br />confirm the integrity of the entire fuel delivery system (Tank, bulb, gas lines, fuel pump and your rebuit carb)<br /><br />after the above, if there's still a problem, then its time to move on to the electricals.<br /><br />we'll wory about that onece you get there.<br /><br />let us know what you find. lots of folks here who are willing to help.<br /><br />sorry that i'm not familiar with your motor specifics HOWEVER, a manual will have info on recomended and alternate plugs.<br /><br />Good Luck<br />HAVE FUN!

 

[Jack Shellac]

Re: 1989 johnson 150 gt help

The recommended plug [by OMC] is a Champion QL77JC4. Alternate is Champion L77JC4. Both gapped at .030".

 

[jrc27]

Re: 1989 johnson 150 gt help

well guys, took the boat to the lake and noticed a bit of difference just by adding treatment to the gas.. ran the boat a while, added decarb to the carbs let her sit for about an hour and a half and ran again, changed plugs after this and WOW!! i gained between 10-15 mph.. had it to about 55-56mph now without the surging i was getting before.. idles smoother also.. <br /><br />the only problem i have now is that i got that increase but not a wot.. still had some left but my rpms were around 5500-5600 and still had some trim left also.. i was told that this motor redlines at 5500rpm.. is it bad to run at that or are rpms at a higher redline than i was told.. will it shut down at redline? also how can i get my speedo to stop jumping so much at high speeds?

 

[farginicehole]

Re: 1989 johnson 150 gt help

jrc27,<br /><br />Just curious as to what type and size of boat you are talking about here? I have a '89 Evinrude 150XP, and only get about 40-41 mph at 5000 rpm on my Alumacraft 185CS Competitor (a side console walleye boat). I have had it for a couple of years, and had the compression checked when I got it. It seemed a little low, at somewhere around 105-110 for the lowest cylinders as I vaguely recall, but no really big deviations between cylinders. It also ran really roughly, so I had the carbs rebuilt shortly after I bought it (cost around $350 if I recall correctly). This smoothed it out quite a bit, but still no increase in top speed or rpm. It still has the original 15" aluminum prop, which I think is a 19 pitch or maybe even a 17? I'll have to look again. At any rate, I've been reluctant to invest $300+ on a stainless one, given that I only get 5000 rpm out of this one and may see no real performance gains. I'm getting ready to put new plugs in it, and may do the decarb thing too. If you could tell me exactly what you did as far as the decarb goes, I'd be most appreciative! Also, what "treatment" did you add to the gas? Did you go with the Champion QL77JC4 plugs? Friends were telling me to go with NGKs, but folks here told me to stick with the Champions for the Evinrude. I've just accepted the fact that my boat is slow, but now you've got me doing more thinking about how 40 mph for a 18.5' walleye boat and a 150 "just don't seem right!" Sorry about all of the questions! You can e-mail me at brianjheine@eaton.com if you want, as I see that there is no way for me to receive notification of replies to this message. Thanks and good luck!

 

[kenimpzoom]

Re: 1989 johnson 150 gt help

Dont trust the speedo for being accurate. Only trust a GPS speedo.<br /><br />Ken

 

[Dhadley]

Re: 1989 johnson 150 gt help

Your target rpm at WOT is 5900 with an average load.<br /><br />Since running cleaner thru seemed to help it indicates dirty carbs. Not unusual after sitting that long. If it were mine I would clean the carbs and install new kits. If its not getting enough fuel then its not getting enough oil and therefore its possible to trash a piston.<br /><br />Good luck!

 

[farginicehole]

Re: 1989 johnson 150 gt help

Kenimpzoom,<br /><br />My GPS agrees very closely with my speedo. Since I had my carbs rebuilt shortly after I got the boat and didn't realize much if any gain in rpm or top speed, I'm wondering if the decarb and new plugs will help me at all. Guess it's worth a try.