2001 40hp Merc rattling and not pumping water

Hi There, wondering if I can get some ideas on my motor problems. Every now and then when I start the motor it will tick/rattle from the spark plug end of the motor. When it does this it does not pump water. If the motor is then turned off and restarted it will run fine and pump and not rattle. It will then run like normal until it is restarted and radomly have this problem. Has been doing it since I got the boat 1 year ago. Has been used heaps. Its a 2cyl single carb. Thanks for any ideas. Matt

Re: 2001 40hp Merc rattling and not pumping water

Same situation I had...in my case the impeller was binding.I was told to try first blowing compressed air through the "pee hole" because sometimes spiders or debris can plug it up.However in your case I would think you need to replace impeller(not an expensive fix).Mine ran $115 to have a marine shop do it.

Re: 2001 40hp Merc rattling and not pumping water

Did yours make a ticking/rattle aswell? and a stop start fixed both problems?? Cheers Matt

Re: 2001 40hp Merc rattling and not pumping water

First replace the impeller and check the poppit valve and t-stat.

Re: 2001 40hp Merc rattling and not pumping water

Hi FaztBullet, Im just going to try to get it doing it again on the muffs so I can check that its not running backwards although thats far fetched. Wanted to check this before pulling it apart. I will replace the impella and t-stat this weekend, but what and where is the poppit valve? Cheers Matt

Re: 2001 40hp Merc rattling and not pumping water

Right next to the thermostat. Here is what it looks like on a 75 HP engine.



The water pump impeller cannot run backwards. It can only fail to work or fail to pump adequate water.

Re: 2001 40hp Merc rattling and not pumping water

matt95 said:

Hi FaztBullet, Im just going to try to get it doing it again on the muffs so I can check that its not running backwards although thats far fetched. Wanted to check this before pulling it apart. I will replace the impella and t-stat this weekend, but what and where is the poppit valve? Cheers Matt

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Interesting that your checking to see if it's starting backwards. I think it's an excellent check to do. The two cycle engine does have the ability to start and run either clockwise (forward) or counter clockwise (backward). If it wasn't for the devices that are dependent on the crankshaft and dependent on it's intended rotatational direction, it would do so quite well provided that ignition timing was properly compensated.

Since timing is not compensated in this case, if it is running backwards then timing would be reversed btdc becomes atdc and this could well be the source of the rattle. As for the waterpump failing to pump water, I'm not sure, I've never looked at it's design close enough to determine if it would or would not.

Re: 2001 40hp Merc rattling and not pumping water

T-Stat and water pump all good. Need to wait till it does it again and see if its going backwards. Will report back. Cheers Matt