I'm going to try and enlist everyone's help again. I have been following FreeBeeTony's threads and think we have the same issue. I could be wrong on that though.<br /><br />I have a 1995 Mercruiser 3.0 with conventional Prestolite ignition. I have this engine sitting in a 1974 Rally (built by Mirrocraft) 17' bowrider. I have the engine mated to the original 1974 pre Alpha transom plate and outdrive. I am also using the 1974 manifold and Rochester 2GC carb. I am using the old parts with the new engine to mate with the exhaust elbow and transom plate.<br /><br />This is what has been done;<br /><br />-Carb rebuild<br /><br />-New fuel lines between tank and pump.<br /><br />-Fuel tank cleaned out and verified good.<br /><br />-New fuel filters about thirty times it seems!<br />Complete new ignition system installed 8 deg BTDC and 40 deg dwell.<br /><br />-New valve springs on all cylinders<br /><br />-New spark plugs gapped correctly<br /><br />-Vaccumm is at 18 with a slight flicker when on the hose at idle (650-700RPM)<br /><br />-Vaccumm is abo****ely rock solid and steady at 19 when fast idled at 1800-2000.<br /><br />-Timing advance verified and working perfectly<br /><br />-Complete exhaust system verified to be clear of obstructions.<br /><br />This is the symptom;<br /><br />When placing a lot of load on the engine, the engine 'bogs' This is dependent on throttle position, NOT RPMs. If I bury the throttle as one would when pulling a skier out, the engine bogs. This bogging from out of the hole is usually around 1900 RPM, but it really has nothing to do with RPM. If I nail the throttle from 2500 RPM, it will do the same thing. If I slowly take my time and let the boat get out on plane with about half throttle, it will eventually speed up to about 3200 PRM where it runs beautifully all summer long. No popping, no bogging, just perfect. If I then try to add more throttle, you can hear the 'throaty' sound from the carb, but no more RPM. If you add more throttle, it will bog harder and you can see that the exhaust gets black and smoky. Somehow the air/fuel ratio gets out of whack and if I hold it in that 'bogging' area, it will eventually die by flooding. Once the boat is on plane and I start to trim the leg out, it will creep up to around 3800 RPM with full throttle, but it bogs a bit first, then clears it's throat a bit and goes to 3800 RPM. About 30 MPH. You can then feel the engine surge a bit at this speed. Throttle buried, it is very throaty sounding, and surges a bit, like it's going to develop full power, but it still just keeps this bogging feeling and sound.<br /><br />This is probably way too much information, but I am trying to be as descriptive as possible.<br /><br />I have done everything people have recommended me doing this summer and I would like to find out what it is.<br /><br />I am stressing that this symptom happens and any engine speed, not just at high speed since it seems people keep looking to valve float or other things. This is a throttle position, or load on the engine situation. What could cause such a major either over fuel situation, or under air situation because I saw the exhaust with my own eyes last night from behind the boat at speed from a tube and it was puking black smoke while my wife was killing the engine by applying too much throttle! If you back off the throttle during the 'bog' it clears up and runs well again.<br /><br />Thanks for everyone's help!<br /><br />Nicholas
