5 and 7 cyclinders are right next to each other and also fire after each other,this is why alot of people miss this and its not very noticeable,follow the wires with your hand from the plug to the cap!From looking at the front of the motor were the water pump is if you run one,5 and 7 are on your right side,7 being the furthest back! even cylindres are on the left,odds on the right hence 1 is the closest to you on the right side!

18436572 good luck

Thanks for the glimer of hope but no such luck. I just double and triple checked the wires tracing them from cap to plug and back and confirming against 1-8-4-3-6-5-7-2 fireing ader and all were/are correct. I was running AC plugs before but the NGK's are a direct cross. Are my gaps ok at 040? the ones I pulled were even wider at 042, I wish I would have held onto them so I could reinstall and try.

How about pulling one spark plug wire off at a time while the engine is idling? If you get no change in rpm from a wire- that cylinder isn't firing. Be carefull not to shock yourself- use a heavy rubber glove.

your mufflers/exhaust have nothing to do with the RPM, and the RPM is driving the reduced speed (I bet you used to be 56 mph at 46oo RPM as well)....

Look to the plugs or soemthing else that just happened to come up at the same time....

Going to run it with a scan tool today.

We may have hit the answer. Since getting the boat last year I've had a problem with it not warming up (posted here about it a few times) and could not figure out why - didn't worry too much as it ran well. Yesterday air temp was about 50 and water temps were very cold - snow run off 4400' elevation. Ran it on the scan tool today and it would only warm to 70 and was throwing a cold temp code. Pulled the thermostat housing and the retaining sleeve that directs water was missing (I didn't even know there was supposed to be one) put one in and the boat warmed right up to 162. Also found timing to be a couple degrees off so that was reset as well. I'm going to run it out to the lake again tomrrow after work and test it. This time I'll take my tools and a fresh set of plugs in case.

I once had a bad spark plug, new right out of the box. It fired at low speed not under maximum load. It wasn't until I put a new set it months later that it ran right. A spark plug wire could also be damaged, check the resistance.

Dumb question - how do you test resistance?

Did you pull the distributor cap and look in there? Could be part of the problem. I bet you'll run a little better with warmer water in the motor too though