Yamaha 40hp. Runs fine 5 min, then hi end dies

[cleanriver]

Hi. My 1992 Yamaha 40hp (C40R) 2cyl runs like a top at the high end for the first 5 minutes. Then..."RRRRrrrrrr", it just loses power, and will only max out at maybe 30%. Pushing the throttle past that causes it to die even further. <br />I have to let it sit for a long while (hours, or longer) before I can get it to power up to full throttle again, and then the same thing happens again.<br />I have cleaned the carbs with carb spray, and I replaced the fuel hose...neither of which did anything.<br />Many thanks for any insights.

 

[rodbolt]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

sounds like its running out of gas, has the fuel pump been serviced? how much tools and experience to you wish to aqquire? have you tested the alaem system ?<br />is this a tiller handle motor? the R you posted can mean 93 or tiller but it actually should have one more alpha characters. cleaning with carb spray while they are on the motor is a waste of carb spray. but it sounds like your running out of gas

 

[cleanriver]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

Thank you, Rodbolt.<br />You are right, I double checked and its actually C40ELRR.<br />I dont believe the fuel pump has been serviced.<br />If it's not too huge a job, I'm game to try my hand at this...I think I can borrow some specialty tools if needed. If we indeed think the problem resides there. How big a job is that? <br /><br />It is not a tiller handle. I have not tested the alarm system, and to be honest, I am not sure how to do that. I would value your advice.<br /><br />Before I go looking at the fuel pump, does it sound like this could in any way be related to the fuel tank? Its a portable plastic tank. I was wondering if it could somehoe be related to air flow? I have had the same problem with the air vent set to open, half, and closed....kind of grasping here, but I thought i'd just ask you, at the risk of looking foolish.<br /><br />Many thanks

 

[rodbolt]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

to test the alarm turn the key on, the dissconect the pink wire from the overheat switch on the cyl head. ground the engine harness side of the connector and you should hear the horn. if not we have to correct the alarm system for further testing. the fuel pump is easy to rebuild but its about as chep just to replace it. once we make sure the alarm system is working we can continue to test.

 

[cleanriver]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

Thank you Rodbolt.<br />I did as you instructed and Yes, the alarm sounded. First time I ever heard it !<br /><br />I really appreciate your assistance, and will look forward to your further instruction.<br /><br />Best Regards

 

[rodbolt]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

ok now we know the ystem is capeable of working I would concentrate first on the fuel side. when it starts dying out does it help to have someone rapidly pump the primer bulb? if it picks back up look at the fuel system to include both side of the quick connet the engine fuel filter the hull mounted filter,if any. if the bulb is physically being sucked flat look from the draw tube in the tank to the bulb. you can also use an oil can with premix in it and spray directly in the carb, if it picks up look at the carbs or the fuel pump.

 

[cleanriver]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

Rodbolt,<br /><br />OK, we took the boat out today and did as you suggested. Here are the results:<br /><br />It ran fine for 10 mins, then died off as usual. The bulb did not go flat, and pumping the bulb did not help the engine rev any higher.<br /><br />We also changed fuel tanks, to no avail.<br /><br />So, we took the cover off the carbs and sprayed premix directly in. This immediately worked, and the engine revved to full throttle and stayed there as long as we kept spraying.<br /><br />One twist: If we sprayed into the lower carb, it flooded out. Spraying into the upper carb worked fine.<br /><br />So, I think you said this points to fuel pump or the carbs. Any thought on how we can troubleshoot between them ?<br /><br />Many thanks for your help.

 

[rodbolt]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

most likly trash in the upper carb, do them both and the fuel pump as well. you will get the same symptoms with a weak pump but by using the fuel primer as a pump with no change I lean towards trash in the carb or a restrition in the fuelbowl inlet.

 

[cleanriver]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

OK. When you say to do the carbs, is that a disassebmly and cleaning ? Is that something that requires special tools? I'm a novice to this, though fairly mechanically able. Don't want to get in over my head, though.<br />Many thanks

 

[rodbolt]

Re: Yamaha 40hp. Runs fine 5 min, then hi end dies

no special tools, attention to detail and cleaning but no special tools.<br /> but yes the only way to clean the important parts is to dissasemble the carbs.