BOAT PROBLEMS!

[spin-a-bait]

I have a '90 150 Johnson GT on a 19ft Bass boat recently the boat has been getting on plane really slow,most of the time I my passenger has to get on the bow to get on plane but once I get on plane it feels strong as ever....but my top speed has decreased alot also..when I first got the boat it would do over 60 but now 54mph is about all I can get...I have a 4 blade stainless prop....I also tried another prop that was brand new and it was a size smaller but it did not help....The thing is that the motor has always ran about 5500rpm WOT when it use to run 60 it did 5500prm & now when it only goes 50-54 it still runs about 5400-5500rpm......how can I lose that much speed and that much hole shot & still run those rpms??

[RUSTY63]

Welcome to the BBC.

Check the compression, all cylinders should be even.

Check the exhaust plate, its in the back between the cylinder heads, see if any bolt are loose at the bottom and up the right side from the bottom, also see if the gasket is hanging out.

With the motor off, advance the throttle and see it the timing advance moves at the same rate as the throttle arm, sometimes the grease gets hard and the timing will advance slow, this would cause the motor to be sluggish on take off.

Remove the air box and make sure the throttle plates are opening completely.

[spin-a-bait]

The compression readings are 100,100,100,100,85,95

[RUSTY63]

That 85 and 95, I would look in the cylinder and see if there is any damage, you can do this with a flex light through the spark plug hole.

[spin-a-bait]

Well guys I took my boat to the shop today so I will keep yall updaten on the problem