Johnson GT 150 not getting up to speed.

[silverwing_6]

I have an 1989 procraft 18' bassboat with a Johnson GT 150. I have had it for 2 years, and it would get up to 65mph fully loaded. Now it won't go faster then 45mph unloaded. Every time this happened before I would take appart the carbs and clean them out, along with the hoses and pluges, then it always worked after that. This time it wouldnot go faster then 30mph, after I repeated the process it got up to 45 but no faster. I triple checked my work and found no problems. But I did notice that while under power and keeping the boat strait it went 45mph and when I turned the boat slightly to the right it went up to 47mph.<br />What am I doing wrong, if any, and how do I fix the problem?

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

Oh yeah, I do have a stingray fin on the motor which I installed last year, and the stearing weel has become slowingly harder to turn over the past 3 months.<br />Thanks for any help.

 

[v12mac]

Re: Johnson GT 150 not getting up to speed.

If you keep having to clean the carbs, wouldn’t that suggest that you have dirt in your tank or bad gas going in? Do you have a good fuel filter in line somewhere?<br /><br />On the pull to one side check you’re steering trim tab just behind your prop, it could have slipped.<br /><br />What is going on with your RPM?<br /><br />Mac

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I have a filter in the tank and just before the carbs. I also have a fuel water seperator, all of wich are good. I did find a fuel line passed the filter just before the carbs the last time I cleaned them that was rotted onthe inside. I replaced it and flushed the line. This was the main cause of the blockage.<br /><br />The trim tab was bolted by 3 bolts with the installed fin so it could not have possibly moved.<br /><br />I don't know, my tack does not work.

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

Does anybody have an idea?

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I'm stumped how about yall?

 

[Walker]

Re: Johnson GT 150 not getting up to speed.

You nedd to do a compression test to rule out a bad cylinder

 

[marinemech]

Re: Johnson GT 150 not getting up to speed.

also check spark to all cylinders<br />make sure throttles are opening fully

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I did a compression test after I took off the cylinder heads, cleaned the pistons,the heads and replaced them. No leaks, rings are good, compression is good, spark is strong and on time, trottle is properly adjusted and opening fully. Just to be on the safe side I even took it to two different outboard mecanics I know and they found nothing wrong. They are at a loss and so am I thats why I am hoping that you guys might know what we are leaving out to check.<br />I have tryed everything I can think of. What am I missing?

 

[ob]

Re: Johnson GT 150 not getting up to speed.

Tried repeatedly bumping the fuel primer button or pumping the fuel bulb when engine won't get up to speed? Fuel restricted carbs or failing fuel pump is my guess.

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

Thats what I thought so I replaced the bulb and the fuel lines including all the lines connecting the carbs and the fuel pump. I also pressure tested the fuel system. The pump is going strong and so are the carbs. The fuel bulb is staying hard even under full power.

 

[ob]

Re: Johnson GT 150 not getting up to speed.

What if you bump the fuel primer button repeatedly? Does the engine pickup or flood?

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

flood.

 

[ob]

Re: Johnson GT 150 not getting up to speed.

Well if we're dead sure that fuel delivery is not an issue,which I'd only be convinced of after performing the above checks in conjuntion with what you've already gone over,that leaves compression and spark.Have you inspected the individual condition of the plugs after a failed high speed run to see if they look consistent as to the amount of oil residue?You could be losing one or more cylinders ignition when engine is up to temp. The fact that the carbs have been fouled on more than one occasion which corrected the running problem also begs of a compression test.Fouled carbs on two strokes means oil starved cylinders.Is this engine being run with VRO or are you mixing 50:1 .

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I disconnected the vro when I got the boat, don't trust them, and started mixing 50:1. Sometimes when in a hurry I add a little more oil then it calls for.<br /><br />all six plugs look the same; after about 10min running at idle they are clean, after about 10min running at full power they are clean, no soot or carbon, but a little oil drenched.

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I'll check back tomarrow, Thaks again for any help you guys can offer.

 

[silverwing_6]

Re: Johnson GT 150 not getting up to speed.

I'm back. <br /><br />What, nobody has any more ideas?<br /><br />come on I have to be forgeting or omiting something because it worked fine 2 months ago.<br /><br />Please, any idea might help because 9 times out of 10 the problem is from something small and simple.

 

[ED21]

Re: Johnson GT 150 not getting up to speed.

Are the throttle valves opening fully. Linkage could have gotten messed up. <br />Someone attached the cable to the wrong hole of the lever on my boat. Other ways it can get out of whack too.

 

[G DANE]

Re: Johnson GT 150 not getting up to speed.

Rebuild the carbs, I think you have one or more flooding. When you rapidly turn motor, fuel is moved in bowls and it will get less fuel as high speed jet suck from center. I discovered this, when I forgot to put the little center gasket in a 35 HP carb once. When I turned from side to side it picked the missing rpm´s up. You could also have floater hight set way too high.

 

[G DANE]

Re: Johnson GT 150 not getting up to speed.

My guess is your plugs all look dark brown, they did on the one that was way too rich for mee, it lost almost 30 % topend. Theese carbs much pick up fuel in right side of bowl, fuel will go slightly to left when you turn right, bet you have way too high float settings, or left out a gasket, or leaking needle valves.