1997 Johnson 175

[ollison]

I have a 1997 Johnson 175 on a 92 19.8 Champion and I am dissappounted at 61 MPH at 5800 RPMs. I am wondering about a problem on top end. If I hold it at 61 for about 2 miniutes she shuts down but always restarts on the way down. I have checked the filter and it is clean. Is this a rev limiter. I thought it would be at the Mid 6000 mark. What can make my boat alittle faster?

 

[Faztbullet]

Re: 1997 Johnson 175

The shutting down sounds like a fuel problem. Your running pretty close to max set up on that hull. From your info looks like a 22 pitch prop your running @ 3-4% slip. A jack plate will help but only a couple mph. To go faster you need more cubic inches

 

[ollison]

Re: 1997 Johnson 175

I have a 4 blade 24 inch pitch..

 

[Dhadley]

Re: 1997 Johnson 175

With a 24 you're at about 19% slip which isn't too good but lets look at the motor issues first. The rev limiter won't shut the motor off, it just won't rev any higher. Most are so smooth you don't even confuse it with a miss. However, if yours is shutting off, that a problem.

When it happens do you lose the tach reading too or does it continue to work?

 

[ollison]

Re: 1997 Johnson 175

Next time out I will try to note the tach. I have a hydrolic Jack plate and was wondering how to work it for top end. All the way up if you would draw a line from the very bottom of the boat the prop shaft would be 3 to 4 inches lower than the bottom line of boat. Is the jack plate high enough?. Do you trim the boat first and then lift the plate for top speed?

Thanks for your expert help.

 

[Dhadley]

Re: 1997 Johnson 175

The optimum height you'll end up at - for any speed - depends on your hull design and how it reacts to your prop design. It's not at all unusual to have the jackplate very high at mid range and then lower it as you go faster due to the hull lifting more. Finding optimum height for max speed at a given throttle setting is found by playing with both trim and height in small increments.

Also it's not unusual to see a flats boat with the plate all the way up and throwing a huge rooster tail which is - as we all know - very inefficient. But most likely he's running across shallow water rather than looking for top speed.