Couple of Questions About a Yamaha C40

[abnredleg]

I have a 1995 Yamaha C40, I have had some trouble with it lately and did a number of things to try and fix it. If any of you all can help I would appreciate the input. Here is the issue:<br /> The manual says that the RPMs should be between 4,500 and 5,000 when at WOT. Right now I am only getting to 3,500 RPMs. I have a 9 pitch prop on it and running it on a Sprint 255 boat (Approximate weight 1,200 lbs) I did have a 12 pitch on it and it ran even less RPMs (2,000). I don't know if it is the popet valvue or spark plgs/wires. I did put new spark plugs in it and it still is not doing anything. The fuel filter is clean. Can someone tell me how to check/clean the popet valvue. I am at a loss for what it could be.<br /> Thanks,<br /> Chris

 

[rodbolt]

Re: Couple of Questions About a Yamaha C40

you have a 40 on a 25 ft boat? <br /> are you sure your tach is set correctly?<br /> try running some of the high thrust pontoon boat type props. You will have a bit of trouble ever planing this rig. its underpowered.<br /> try to use the test wheel yb1611 to insure the motor can make power before you spend anytime chasing ghosts.tach setting on your engine is 4 pole or 2 pulse. its differnt than most others.<br />have this motor tested by a competent professional that has a known good shop tach and the proper test wheel or dyno. lets make sure your only problem is overpropping.<br /> good luck and keep posting

 

[abnredleg]

Re: Couple of Questions About a Yamaha C40

Originally posted by abnredleg:<br /> I have a 1995 Yamaha C40, I have had some trouble with it lately and did a number of things to try and fix it. If any of you all can help I would appreciate the input. Here is the issue:<br /> The manual says that the RPMs should be between 4,500 and 5,000 when at WOT. Right now I am only getting to 3,500 RPMs. I have a 9 pitch prop on it and running it on a Sprint 255 boat (Approximate weight 1,200 lbs) I did have a 12 pitch on it and it ran even less RPMs (2,000). I don't know if it is the popet valvue or spark plgs/wires. I did put new spark plugs in it and it still is not doing anything. The fuel filter is clean. Can someone tell me how to check/clean the popet valvue. I am at a loss for what it could be.<br /> Thanks,<br /> Chris

 

[abnredleg]

Re: Couple of Questions About a Yamaha C40

Sorry the boat is not a 25 footer, it is a sprint 255 bass boat about 16 ft in length. It had a 9 pitch prop on it when I bought it used and it ran fine. Took it into the shop and they fixed the cracked starter housing on it and said it should be a 12 pitch prop on it. Tried that and that is when the RPMs started messing with me. Changed the oil in the lower unit also and no metal shavings in the oil. I was scared it was the lower unit. Went back to the shop and they said to put the 9 pitch back on and it should be fine. Did that and the boat is still not running to the max RPMs only about 13 MPH off a Garmin. Thanks for anymore help/ideas you may have.

 

[jim dozier]

Re: Couple of Questions About a Yamaha C40

My guess is that you've dropped a cylinder. Now you just have to find out why. Spark or fuel or compression. Maybe you carboned up the engine with the 12 pitch prop. Begin at the beginning. Since it ran fine before the work on the starter housing you may need to have a conference with the mechanic that did the work.

 

[rodbolt]

Re: Couple of Questions About a Yamaha C40

ohhh ok<br /> how long did the boat sit while waiting. gas can gum up the carbs in afew weeks under certain conditions.<br />it could also have picked up a bit of water in the fuel. post any other trouble shooting trials you have made.<br /> good luck and keep posting but its esiest to start with the basics first. make sure the motor can make power before to much prop swapping