I had same problem on my 358 this summer. I cleaned my air filters and changed the fuel filters. I gained most of the speed back. I will change the plugs and probabley get it all back.

I pulled off the fuel filters and found a little water in the stbd one. I will get new and test the boat tomorrow. I don't have the tools at home to cut open the filters but I'll bring it home tomorrow. I have K&N spark arrestors, I just serviced the filters a couple weeks ago. I will check the plugs, they are 2 year old GM Rapidfires, may be time for new. The heat and humidity are lower now than prev. I don't think its the ignition, but now that I think of it , it is time for new caps and rotors (original)!! Thanks for the help everyone!

I bought the tune up parts but the thunderstorm here is going to delay installation until tomorrow. I'm very frustrated!!

I'm sure that it's something simple. How about the oil level . Could you have overfilled by a quart or two by mistake. Also don't be fooled by the fact that both engines are down. A Bad valve spring on one motor will drag down both motors at top end for example. Check that both motors have the same RPM's through out the Rpm range with the same throttle position. Otto

I got my RPM's and speed back yesterday. As a matter of fact , in the cold am (60) I was bouncing off the rev limiter and had to pull back. I like that much better than under revving!!! I had restricted fuel filters, only 31 hrs old. I also pulled out the 80 hr old Rapid Fire spark plugs (platinum, supposed to make power and last 200 years) that looked like crap and cost $4.50 each, and made no discernable running change and replaced them with $1.50 each NGK's that are working great. Also I replaced the caps and rotors because I had forgotten about them . Thanks everyone for the help, I was thrown for a loop because the way the boat felt when it was acting up was very strange and confusing, not like it just needed a tune up. Its really nice to have everyone help by looking at it from a different angle and share their experiences.
THANKS, Chris

Great, glad it was something simple, enjoy that boat, I think I am going to replace my fuel filter it has 45 hours on it, still runs good but it is time

I was going to be a smart ass and tell you to push harder on the sticks.............glad you found you're problem. And you also reminded alot of us to change our fuel filters!! Going to do that now!!!!

Ultra trick spark plugs are just gimmicks.

NGK/ND/AC/Motorcraft/Champion/Bosch - all make fine plugs in the "normal" category.

I HAVE heard not to use the "small tip" platinum plugs in many applications (namely boats).

A plug with 6,200 separate electrodes, each with a scalloped edge and a groove up the channel that will pick up 3 cabel tv channels is still just a spark plug.


If a plug is the correct heat range, is gapped for the application, and is clean and being fired by an ingnition system that is working properly, thne there is not much to gain with a gimmick plug.

Save your money and just keep spares handy. I change plugs every spring after a run to burn off the motor fog. They always look like they are new.

3 Cable channels........Where can I get them!!!!