I just took a 2003 Larson 330 Cab for a sea trial, it has twin carb 5.7 Mercs rated at 250 hp per. It had full fuel (220 gal) and some gear and water, 3 men (total 600 lbs) It would plane off very quickly but would only run 38MPH at WOT @ around 5k RPM's...it also seamed to have prop cavitation at the slightest bit of up trim over about the 1/4 mark of trim. Tabs were used in full down position then raised to full up position once on plane, then I would trim the props up slightly and if I went past 1/4 up they would spin and start losing speed. The mechanic riding in the boat said i did everything right and that i shouldn't expect more top end from this boat with the propulsion setup? The web forums I read said to expect 43-45 at WOT? Any thoughts? Thanks in advance, Mike
Hi my name isXXXXX will assist you.
First off the props are not the right props 5,000 rpms is way to high for those motors. If you put the correct props on you might get the right speed. Don't believe everything you read in the forums people like to say their boats run faster they they actually do. Now if the bottom has paint on it or if there is any growth on the bottom all of this is to be taken into consideration. The load has allot to do with speed also. Fuel and water add allot of weight and will slow the boat down. If you had half the load and the correct props you will most likely get the speed they say the boat is getting.
The boat has no growth and brand new bottom paint.....what should WOT RPM's be?
I will need the engine serial numbers, but I believe on the 250 hp is 4400-4800.Tan Partin41040.0944121528
I don't have them handy....can "over revving" do long term damage to the drives or engines...I love the boat, should this be a deal killer? <-----Last question and thanks in advance
I looked at the 250 all are 4400-4800. The engines over reving long term will cause damage but there is most likely no damage done yet as most people don't run there boats at full throttle all the time it sucks the fuel. These engines are very durable. But the props should be changed. I would go up in pitch by 2 to 4 inches of pitch to get you in the correct rpm range. No that shouldn't be a deal killer if you like the boat just before you purchase the boat get the props taken care of before you buy the boat and take it for a ride.
35 yrs. experience. I/O, Outboard & Inboard, Complete engine repairs.Certified Technician