TOPIC: Slow Mover

I have a 1965 16' HyrdoSwift powered by a 1959 40HP Evinrude Big Twin. The motor seems to run good but the boat tops in around 10-12mph. Does this sound normal? Would a different prop help?

Greg

How many people on board? Do you have a tachometer, if so give us the RPM @ wot.
It seems a little slow. I doubt if you are even getting up on plane. You may need to go to a lower pitch prop as you may be stalling out the engine. Boats do not have a multi speed gear box so if you are too heavy you need to gear down (lower pitch prop) in order to get on plane. We can't answer that until we get some more specifics 40HP is a little on the lower HP side for a 16' with a heavy load.
You may also have to trim it in to get on plane. If you are not on plane you are plowing which takes more power. My 45 HP 15' will not get up on plane with 3 adults and 2 small children on board without trimming it all the way in. It will then top out at about 15 mph if trimmed out, trimmed in she will go 22 because she gets up on plane. With only me aboard and trimmed out she will do 27 to 31MPH depending on trim and weather conditions.

thanks for the response. Typically it is two adults, a teen and a child. I don't have a tach so I really don't know what RPM's its cranking. I'm sure the motor needs tuned up but I think the prop probably does need to be changed out. I just wasn't sure what prop it should be using.

A couple of things, The 59 motor was a 35hp the 40 came out in 1960, pics or the model # would help. If you have not gone through the ignition system that is the first thing I would do, bad coils, wires and plugs can create all manner of poor performance. Rebuild the carb, replace the waterpump impeller, and once you get all that done get it on the water with just you and a friend and really dial it in. Start with the low speed 1 1/4 turns out from lightly seated and the high speed about 3/4 out. After starting adjust the low until you get a smooth idle at low speed but the motor doesn't "cough" and then take it out to adjust the high speed. To set the high speed run it at full throttle and adjust until you get max speed then back it off towards rich just a tad. Set the trim one one out from the bottom to try it and then adjust it out to see if that increases speed without allowing the prop to blow out on turns. A prop chart with all sizes for the big twin is on propcopropellers.com more pitch for a light boat and load and less pitch for heavy hulls or loads.
Al

One more thing check to see if you are achieving wide open throttle. When the lever is forward are the butterflies wide open.

Check your mounting also. The tilt of the engine will make a difference big time. A guy showed up at the ramp once trying to get his boat working. He could not get any speed. Anyway he had a short shaft on a long shaft boat. He had no idea. He did get a long shaft motor and run it over the rocks a few months later. Learning curve was harsh on that one. Never saw that fellow again. I think he gave up.

Thanks for all the responses. The title says it is a 59 but it is clearly labeled a 40HP so the title may be wrong. It has set for a while; it will start and run but only slightly more than an idle. I'm going to see about getting it to a mechanic and see if I can get it straightened out.