MrTotty said:
Interesting you say that. I spoke to the third person at Mercury and explained I needed to talk to someone very familiar with that motor. This person agreed that the RPM's were low, and talked to a product specialist who also agreed they were low. His fix was to order a new Merc Impeller, that most likely the one that is on the boat was an older model that had not been modified for the four-stroke. More to come...
Any update on your motor's performance with a new impeller? I ask because I'm going through the same hassle that you have had. I also have a Lowe 1655. About a month ago I replaced my 2005 2 stroke 40 Jet with a new Mercury 4 stroke 40 Jet. When I got a chance to get the boat with the new motor out on the water, max RPM at WOT was 4500 and top speed was around 22 mph. It would just barely get on plane. I took it back to the dealer. After about a week and a visit by a Mercury Tech Rep to check it out, they finally gave up on trying to find the problem with the motor and shipped another one from the factory and put it on my boat. The new replacement still doesn't run up to the RPM specified which is around 5500-6000. At best it runs around 5200 at WOT, usually less and the top speed is only around 26 mph on still water. The dealer says that the motor will run at a higher RPM after it is completely broken in. I have doubts about this.
I replaced my old 2 stroke because the powerhead needed rebuilding and I didn't want to put a lot of money into it. I'm beginning to think I would have been better off going with the rebuild. Back when it was running right, the 2 stroke ran 5250 RPM at WOT and got around 28 MPH top speed.