RPM's max out at 2500

[prockvoan]

In my boat I have twin 350 prevortec mercruisers with TB IV inboard engines.All plugs,wires,distruber cap and rotor,coil have been change,new carb,risers new,temp running at 160.Fuel filters new,tank clean out and the list goes on and on.This engine has around 100 hours running time on it.WOT was 4100,now it will not go above 2500 rpms when under way.When out of gear,it will go above 4200 rpm's.<br />Timing set is 8 BTDC and at 3000 rpm's,it set at 27 drg.The carb is a rockchester 4 barrel,I had clean the air breather,ran a compresion check,all cyl are at 150 to 157.Plugs are black,using NGK BR6FS,set at .35.<br />I had swap out carb's,and all other elec parts from other engine with no fix.<br />One question I am thinking of is;if my battery power would be low,less then 12V would that make a differnce?

 

[jeff13601]

Re: RPM's max out at 2500

The only way the battery would affect it is if your alt is gone. The black is rich burning or oil. Has the boat always run this low of rpm on both motors?

 

[Don S]

Re: RPM's max out at 2500

How long has the boat been in the water, and how dirty is the bottom?

 

[Haut Medoc]

Re: RPM's max out at 2500

Exhaust restiction? Do you have flappers? If you do not you may have them stuck in your exaust. If you have new ones you may have an old one stuck there....If you have a lot of growth on the bottom/drive it would not help..........J

 

[FreeBeeTony]

Re: RPM's max out at 2500

See my other post ..........if the exhaust restriction is suspected I would go right for the vacuum test............<br /><br />I haven't confirmed it but I'm 99% that this is my priblem