2questions for the guru's?????

[albass]

1st is there any way to get more trim out of a 1991 Johnson Fastrike 150hp Ican get to 5500rpm's but no matter how much I try can't get any more also after all the work done by dealer I still have a low speed skip or idle range of about 2 to 3 hundred rpm's he didn't rebuild the carbs should I or just live with it it runs great at any other throttle position WOT is 5500rpm's 63MPH by gps it is on a Ranger 374V 18' bass boat

 

[Joe Reeves]

Re: 2questions for the guru's?????

The PTT trim is set for 15° of trim range and can't be changed.

Idle at two to three hundred rpms? I'm surprised it ran at all. The engine is not designed to run that slow. Usually idle, the lowest rpm in gear is somewhere around 650 rpm.

 

[albass]

Re: 2questions for the guru's?????

The PTT trim is set for 15° of trim range and can't be changed.

Idle at two to three hundred rpms? I'm surprised it ran at all. The engine is not designed to run that slow. Usually idle, the lowest rpm in gear is somewhere around 650 rpm.

no the idle is around 800 but it drops 2 to 3 when it skips then goes back to 8 then down to 6or51/2 then back to 8 ok

 

[tashasdaddy]

Re: 2questions for the guru's?????

pull you air silencer off and see if the butterflys are fluctuating. could worn bushings in the linkage.

 

[Dhadley]

Re: 2questions for the guru's?????

Sounds almost like you're dropping a cylinder or two at idle. If it's running on 5 at wot that may be why you can't get any more rpm.

There's no reason that you can't get more rpm if the motor is running properly. You may have to raise the motor or play with set up but the rev limiter is at either 6200 or 6700, depending on which ignition components you have.

The other thing to check is the tach. To get 63 with that motor on that boat you'd have to be running a 23" prop and have almost 0% slip. If the speed is accurate (GPS) then the tach might be messing with ya.

 

[albass]

Re: 2questions for the guru's?????

The prop is a 4 blade Shooter 25pitch and it is by gps 63mph and it tops out at 5500rpm's then starts to get squirely but still won't get more rpm's how high should the motor be I don't have a jackplate.

 

[Dhadley]

Re: 2questions for the guru's?????

OK, you're at about 11 - 12% slip. Pretty normal so we can assume, for the moment, the tach is fairly correct. Everything you mention -- low rpm, ill handling -- indicates the motor needs to go up.

Do we see a jackplate in your future??

 

[albass]

Re: 2questions for the guru's?????

OK, you're at about 11 - 12% slip. Pretty normal so we can assume, for the moment, the tach is fairly correct. Everything you mention -- low rpm, ill handling -- indicates the motor needs to go up.

Do we see a jackplate in your future??

What should the engine height be and do I measure from the cavitation plate or somewhere else????

 

[emdsapmgr]

Re: 2questions for the guru's?????

You may be able to extend the trim range if aftermarket-available trim extenders will adapt to your engine. You can run the engine higher, until you loose water pressure to the lower unit. You can visually check your height by observing the water passing under the anti-ventilation plate at high speed. Not unusual to have the water running an inch or two under the plate with a performace prop like you are running. Raising it more will start to expose the water intake holes and the engine water pressure will begin to decrease. Proper height adjustment will take some fiddling, but is worth the effort. At elevated settings, you may get into holeshot prop slippage. When you get into this adjusting, a water pressure guage becomes a requirement so you maintian adequate engine cooling.