93b 43lx missing top end RPM

"I've got a stingray with

"I've got a stingray with a 4.3lx(weber) with 130 hrs on it. I have only been able to get it going about 40mph @ 4000RPM with a 19 pitch prop. WOT is supposed to be around 52mph @4800 21 pitch prop. Running the 19 pitch prop I should have no problem hitting the rev limiter. The engine runs great, does not miss and feals strong, just is lacking that last bit of power to really take off. I don't have GPS but have verified the speed with the pitot as well as my fishfinder (wheel style). Gas is fresh 93 octain, plugs and wires are good. I originally though the 4 barrels might not be working so I rebuilt the weber carb. It starts a little better when cold but has no more power than before. I changed the fuel/water seperator filter as well. It does backfire through the carb occasionaly when cold if I give too much throttle, after a minute or so this is gone and is responds fine. I am thinking my next step would be to check the fuel pump psi and timing advance. Anyone else have advise on what my problem could be?"

"Is this a new problem? Did it

"Is this a new problem? Did it used to be able to hit 52 mph?
Your top speed will depend on the weight of the boat and available power.
I posted an Excel spreadsheet in a topic called "Boat Speed Finder" July 5. You can use that to get a feel for what your top speed should be and what prop is right. Your drive ratio should be 1.81
Is it possible you have water under the floor? If the boat sits in water mostly and is open to the weather, don't rule this out. This can add hundreds of pounds of extra weight and kill performance, when nothing at all is wrong with the engine or prop.
Other than that you should check compression, timing, and the other basic engine stuff to see that it is healthy. Maybe get a service manual if you don't already have one.
Rod"

"Here is the spreadsheet link:

"Here is the spreadsheet link:

http://www.marineengine.com/discus/messages/12486/Boat_Speed_Finder-79780.xls"

"Yeah, I checked Stingray, the

"Yeah, I checked Stingray, they have thier own perf calcs based on the model/engine combo you pick. It even accounts for gallons of gas and altitude. They say 52 with a half tank, 21pitch and 1 adult. I crosschecked with some other owners I know and they all say 50-55. As for water, I do leave it in for about a week at a time, but the bilge is empty and Stigrays have notched style transoms so you can see pretty well that there is no water under the deck. I haven't done a comp check, I suppose I could; cheeper than buying a fuel pump without cause. I hadn't bothered because of the low hours and otherwise great running and such. Thanks for your suggestions!"

"I ran yours, the output is ne

"I ran yours, the output is near identicle to stingrays.."

"Sounds like you need to perfo

"Sounds like you need to perform some basic engine health checks.
For an engine to make power it needs:
-plenty of clean air
-clean fresh gas
-good compression
-healthy spark at the right time
-as minimal exhaust restriction as possible

You should go through these items and test each thoroughly. Likely one of them will answer your question. Also I suggest a vaccuum gauge test. That will tell you if you have any bad valves, rings, etc.
Rod"

Rod:

I'll bet the timin

Rod:

I'll bet the timing is off or the carb is lean(backfiring) and the floatation foam is waterlogged.

Jeremy:

Do you have the original boat weight specs.? Weigh the trailer at a feed and grain store first and then the boat and trailer. The difference will tell you how much water is in the floatation foam; 8 lbs. per gallon.

"I'll check the compressio

"I'll check the compression tonight. I'll also -check the timing advance. Oil pressure is good @ about 45 cruising, Idle it's around 20.

I do have the weight specs (1545 + the 4.3 at 890). I would be very surprised if it were water logged. It's never kept in the water longer than a week, always snap covered or garaged, has no hull damage whatsoever, and the bilge is bone dry. How would water get into the foam, and wouldn't I have a hard time getting on a plane? I can plane by myself in probably 2 seconds, though I do have trim tabs. Cruises steady and easy at 3500RPM @ 36 MPH, just doesn't go much faster on the last 25% of throttle. If the foam were waterlogged I would think I'de be pushing some major water. Eitherway, I'll check it out to be sure. Thanks for the advise!"