I have tried running my two motors at wide open throttle in the last few weeks. Both ended up having a loud "rattle" once I reached literal wide open, the throttle having no more movement or fuel to give. From idle to within "97%" of WOT, either engine "sounds" normal: an increasingly loud, but smooth 2cycle "buzz" or hum. As soon as I bottom-out on the throttle, I hear the rattle on top of the buzz. The noise was exactly the same on both engines. The rattle sound could compare to someone playing a drum roll on the flywheel, but really, really loud. Or steel nuts inside a paint can on a running paint can shaker.
I don't like metal-on-metal noises coming from my engines.
So I back off the throttle just a tiny bit, and notice a slight reduction in speed, and the rattle goes away. But at the same time, I'm not at true 100% WOT for that boat.
Given the highly technical description above, should I be concerned about the rattle noises? I read many of the forum "WOT" posts, and have a good idea of where the motor should run relative to boat speed, for example: WOT post. I just don't understand if the extra rattle is normal or a problem.
Background:
First motor is a 1985 6hp Johnson 2cy I purchased in cherry condition 8 years ago. It has always been a one-pull start motor, never a problem. I have maintained it fairly well over the last 8 years. Three weeks ago, I had it pushing a moderately heavy load in my 14' Lund all over a big lake. I don't remember it having the rattle in the past, just hold the throttle all the way over. Motor is not intended to get on plane, just get us moving. At WOT I noticed the rattle, and backed off after playing with the "sweet spot" of no rattle vs. greatest speed. Fresh 91 octane fuel, proper oil mix, cap full of fuel conditioner.
Same thing yesterday with the "new" boat. 16' aluminum Spectrum and 1994 40hp Force with professional service one month ago. I chose a new prop in the "mid-range" of performance recommended by operator's manual closest to weight, speed and use. Everything on the boat checked out great, except for the "rattle". When we finally got to full speed testing and playing with the power trim, I watched the tach. RPM stayed in the recommended 4500-5500 rpm range. On the calm lake, rattle-less WOT was 4500-4800, and with rattle 4800-5100. Once wind picked up, I seemed to get another 300 rpm. I don't know if that was from the choppy lake surface, or the motor burning out some crud, and running better after a while. Fresh 89 octane fuel into carefully emptied tank, proper oil mix.
This boat is for fishing, and I just need to get there. I want to be on plane while traveling long distance, but I don't need to run WOT everywhere. I may need to run 20 to 60 minutes to get where I need to go. Once arrived, kicker or trolling motor is used, and for more time than the main motor. It would be nice to just shove the throttle to maximum, and not have to listen for the rattle and back off until it is gone.
What's the deal with the rattle?
I don't like metal-on-metal noises coming from my engines.
So I back off the throttle just a tiny bit, and notice a slight reduction in speed, and the rattle goes away. But at the same time, I'm not at true 100% WOT for that boat.
Given the highly technical description above, should I be concerned about the rattle noises? I read many of the forum "WOT" posts, and have a good idea of where the motor should run relative to boat speed, for example: WOT post. I just don't understand if the extra rattle is normal or a problem.
Background:
First motor is a 1985 6hp Johnson 2cy I purchased in cherry condition 8 years ago. It has always been a one-pull start motor, never a problem. I have maintained it fairly well over the last 8 years. Three weeks ago, I had it pushing a moderately heavy load in my 14' Lund all over a big lake. I don't remember it having the rattle in the past, just hold the throttle all the way over. Motor is not intended to get on plane, just get us moving. At WOT I noticed the rattle, and backed off after playing with the "sweet spot" of no rattle vs. greatest speed. Fresh 91 octane fuel, proper oil mix, cap full of fuel conditioner.
Same thing yesterday with the "new" boat. 16' aluminum Spectrum and 1994 40hp Force with professional service one month ago. I chose a new prop in the "mid-range" of performance recommended by operator's manual closest to weight, speed and use. Everything on the boat checked out great, except for the "rattle". When we finally got to full speed testing and playing with the power trim, I watched the tach. RPM stayed in the recommended 4500-5500 rpm range. On the calm lake, rattle-less WOT was 4500-4800, and with rattle 4800-5100. Once wind picked up, I seemed to get another 300 rpm. I don't know if that was from the choppy lake surface, or the motor burning out some crud, and running better after a while. Fresh 89 octane fuel into carefully emptied tank, proper oil mix.
This boat is for fishing, and I just need to get there. I want to be on plane while traveling long distance, but I don't need to run WOT everywhere. I may need to run 20 to 60 minutes to get where I need to go. Once arrived, kicker or trolling motor is used, and for more time than the main motor. It would be nice to just shove the throttle to maximum, and not have to listen for the rattle and back off until it is gone.
What's the deal with the rattle?