120 mercruiser problem

"I am new to this site so plea

"I am new to this site so please bare with me if I make any mistakes. I have a 1984 Bayliner Explorer with a dry weight of 2880lbs.fully loaded 3450 including two persons. Problem is I can not get over 2900-3000rpm WOT. HAve done the following: copmpression 1-130,2-125,3-125,4-120,5-125,6-125 taken cold did not change when 3 squirts of oil added to cyls. New reman. distributor, new points, condenser,rotor,cap plugs, plug wires, new coil. Points set to .022 gap timing set to 8 degress, advance goes to 35 degress at 2500rpm New fuel pump, new fuel lines, increased to 3/8" i.d. new rochester carb 2cg model 2 idle mixture jets. new water/fuel filter, new filter at pump, new filter at carb. Idle set at 900rpm in foward gear. Vaccum gauge is at 18 inches at idle. Timming marks steady. Idles great at dock can obtain 4500rpms in neutral at dock. Out drive 1.98-1 ratio it turns freely in nuetral, also can turn driveshaft and prop turns in F or R when outdrive was off to change bellows and u-joints. Prop is 15X17 that is what is recommended by Mercruiser. After doing all this work and replacing many parts I still can only obtain 2900-3000rpm. ALso checked tach against tach/dewell meter only 25rpm difference. Where am I to go from here any help will be usefull."

"I think you may be turning to

"I think you may be turning too much prop. If you are friendly with a boat shop you should try perhaps a 15" pitch and/or smaller prop and see how that goes.
You could check my post of April 24 titled "Boat Speed Finder and Prop Selector" for an Excel spreadsheet that will help you analyze your top speed and proper prop pitch.
Good Luck,
Rod"

Is that gear ratio correct for

Is that gear ratio correct for what appears to be a 6 cylinder you have? Should be around a 1.84. Also a 15 inch prop is rather large for a 6 cyl. It looks as if your outdrive is from an 8 cyl. engine which would explain why you can not get the RPM's you want. My 2 cents
Chris

"David

Its time to play pro

"David

Its time to play props by the sound of it.

Oh and by the way, well done on your first posting, the more info you give, the easier the diagnosis.

Check out Rods excel chart he posted, as he said above, work out what you think is right, then go and chat up your local prop seller and see if he will allow you to try a couple of different ones if you promise to buy one off him.
Or try some of your friends if they have mercruiser drives.

When you have done it, make sure you post your results, your findings will then help others.

Cheers from down under

Peter C"