Boat seems to be missing 10 mph and 700 rpm

[Striper80]

I have a 14 1/4 x 17, I'm pretty sure these are the numbers, apollo prop in my garage. Maybe I'll throw it on just to see. I bought this boat used about 3 years ago and I've only put about 40 hours on it. When I got it the GPS didn't have a speedometer on it so I didn't notice how fast I was going. After two trips I put it away for the winter. Over the winter I had the prop done because the PO nicked the prop. I also got the sei replaced under warranty, did the control cables, and installed the current GPS. My seat of the pants feel was about the same, but it was a bit skewed since I had to do the whole sei break in.
Last year I did the carbs, link and sync, and set the timing, cranking method since I have no test wheel. I had an issue with stalling going from idle to part throttle after that, but I seem have that handled after changing my water separator housing and draining the whole gas tank.
I hadn't thought about prop slip. I was only thinking that changing the prop would change rpm but not overall top speed. Since owning this boat I've always felt that it had less punch than my Striper 2100 WA. That boat was 21 from pulpit to stern and this one is 23, but that boat only had the 130 on it.

[THEFERMANATOR]

By all means try the other prop. Something is definately off with 30% prop slip. That is HUGE for prop slippage at 5100 RPM's. The stilleto I have is a good biting prop that actually has very low prop slippage, and good top end kick. Definately try another prop though, something just doesn't sound right with yours, and you never know if they used the wrong prop block when they redid yours, and messed up the rake when they reworked it. Adding cup would bring your prop slip way down, but it normally costs you top end speed, and you're already turning way to low at WOT(should be seeing 5400-5800 RPM's on that engine to keep it happy, and live a long life).

[Striper80]

Swapped the prop today and saw a best of 31.1 knots at 5100 rpm. Boat was cruising at 28 knots easily at like 4200. Not sure why it won't go any higher. My stalling issue resurfaced though. I think either the pickup is restricted or the pump is failing. The ball gets soft but will get hard when you pump it.

[Destroyer]

Have you done a compression test of the engine after it was warm? If we presume that it's getting the proper amount of fuel and air then compression and timing are the only two things left on the engine that could be effecting the power. Also, you still haven't done a lower final drive ratio test. And what spark plugs are you using?

[THEFERMANATOR]

I think you need to try another tach 1st. 31 knots at 5100 is still pretty high prop slip at 18%. You could easily have a bad tach throwing off your calculations.

[Striper80]

Originally Posted by Destroyer

Have you done a compression test of the engine after it was warm? If we presume that it's getting the proper amount of fuel and air then compression and timing are the only two things left on the engine that could be effecting the power. Also, you still haven't done a lower final drive ratio test. And what spark plugs are you using?

Yes, compression is good and the plugs are correct. The timing may be off as I don't have a test wheel so I set it cranking. Assuming the tach is correct, which I've been questioning, the idle is too high so the timing is off. The boat is idling at 1000 rpm.

[THEFERMANATOR]

You CANNOT set the timing cranking the engine over. There is spark advance built into the ignition module that starts ramping up around 3000 RPM's till 5000 RPM's. The other problem is there is a 6 degree timing advance during cranking until the engine has run for 5 seconds and has reached roughly 120 degrees. You do not need a test wheel to set timing. If you can get it up to 4500 or so on a trailer, that is ALOT better than setting cranking. Not setting the timing right is a GUARANTEED way to burn that engine up. It calls for 18 degrees, if you go over 19.5 degrees, it WILL melt a piston. Even so much as 19 degrees is playing with fire. Most who set these engines up set them to 17-18 at 6000 RPM's. you're better at 17 degrees than 19 degrees. But if you set it to low, it will foul out, carbon the rings up, then you'll stick a ring, and BYE BYE cylinder(some ran at 14 degrees, but they were jetted for it, had MONSTER carbs on them, and were meant to run at 5000+ for sustained periods of time). Get your timing set correctly before you go any furthur unless you want to be buying a new engine. You're playing with fire, and it WILL burn you here.

[Striper80]

My boat has a cdi power pack on it. I thought with this one you were able to set the timing cranking by removing the plugs, grounding the plug wires, using a spark tester, removing and grounding the temp sensor wire, and backing it off by 4* total advance? I'm going to either take it to a mechanic to have them set it or do it at the ramp.
I originally took it to the ramp near my house to set it but the tide was too low to run it on the trailer without dunking my truck. Now the boat is at my marina and the ramp is steep and slippery so I'm not too keen about doing it there. I'm not too keen on paying $145 minimum to the mechanic either. Hey we all have to make a living, but I hate having anyone touch my stuff.