Boat won’t go fast

[Boat350]

I just recently purchased a ranger bass boat with a Johnson gt150 v6 the boat runs like it should on muffs but in the water it will only go up to 3000rpms and about 15 mph is top speed what could my problem be?

 

[emoney]

In the water there's back pressure on the exhaust, could be a number of things. Have you done a pressure test on each cylinder? When was the last time the carbs were cleaned/rebuilt? What year is the motor? Lots of threads around here on this exact topic that may be able to help just spend a little time reading. Post back here with more info if that doesn't help.

 

[oldboat1]

Do a compression test on all cylinders and post results. Measure spark on each lead with an open air spark tester -- look for 1/2 inch sharp spark. If no spark, test continuity of relevant plug wire.

If you do not know when the water pump was serviced, replace the impeller with a fresh one. And...shop Ebay for a service manual.

 

[jimmbo]

You can have 3 dead Cylinders, and it will still run fine on the Muffs. Any Idea how long it had been sitting before you bought it?

 

[Boat350]

It will go to 5000 rpms at home on muffs but not in the water I marked the prop and it did slip about 1 inch could it be the prop

 

[Boat350]

And I will have to buy a compression tester I don’t have one it just really confuses me why at home the rpms will go up but not in the water

 

[boobie]

When you get it back in the water, do a cylinder drop test on it.

 

[racerone]

It would go to 5000 RPM on muffs running on 3 of 6 cylinders.----It proves nothing by doing that.----And it is not good for your motor either !!

 

[tpenfield]

I just recently purchased a ranger bass boat with a Johnson gt150 v6 the boat runs like it should on muffs but in the water it will only go up to 3000rpms and about 15 mph is top speed what could my problem be?

:welcome: to iBoats. . .

You purchased what's known as a 'driveway queen'. At least you now know why it was for sale.

Compression test is a good place to start, followed by a timing check, and a fuel system cleaning.

 

[Boat350]

Done a compression test this morning all6 came back at 65 the motor is a 1986 cleaning the carbs today and check spark at plugs just put new plugs in this morning

 

[racerone]

Compression should be about 110 / 120 PSI.-----So you have a poor quality gauge , bad test method or a motor that needs lots of work.----Carburetor cleaning is always a good thing to do , but may not help this motor.

 

[Tassie 1]

Running you outboard motor at 5000 rpm on muffs can destroy it.

 

[boobie]

Did you ever do that cylinder drop test ????

 

[Djohnson86]

How do you do a cylinder drop test?

 

[racerone]

You remove one plug wire at a time.----Motor should slow down a wee bit with each one.----If nothing happens you have found a dead cylinder.----A V-6 will sound really nice to the untrained ear running on 5 of 6 cylinders.----I dare say there are lots out there that are doing just that.

 

[Boat350]

I appreciate all the help boat is running good now put on a new prop and pulled and cleaned carbs run seafoam through the gas and it will move now