1971 Mercury 7.5 HP Water Pump Problem

I remove the lower unit and cleaned out and replace the old impeller. I installed the new one. It was very tight, but the local dealer said it should fit tight. When I put everything back together it still doesn't pump water. All of the tubes and hoses are clean. I blew them out and the are clear. When I start it just a little exhaust comes out. Anybody have any ideas?

Re: 1971 Mercury 7.5 HP Water Pump Problem

it is real easy to change the impeller <br />and they are usually under $20 <br />if it is a 2000 model and hasent been done yet<br />then its probably overdue<br />if you still have no tattle-tale then<br />hook up the earmuffs and stik a small piece of wire in the pee hole to see if it is cloged<br /><br />i am shure you will get a lot of replies soon

Re: 1971 Mercury 7.5 HP Water Pump Problem

new water pump is already installed. still no water coming out! somebody please help me! does anybody have any schematics they could email me. is there a thermistat on the motor. if so, would bypassing it make it work? i'll try about anything? i am so frustrated!

Re: 1971 Mercury 7.5 HP Water Pump Problem

I don't know your engine particulairly, but it seems most merc 7.5's have a key in the driveshaft to spin the impeller. Is the key present? If you turn the flywheel with the sparkplugs out can you feel the resistance, and mabey hear the squeak from the impeller?

Re: 1971 Mercury 7.5 HP Water Pump Problem

no i cannot. i think that is my problem. i need a key pin.

Re: 1971 Mercury 7.5 HP Water Pump Problem

Hey Barry
seems like you have the same problem like me or I got the same problem like you. I recently got a old 7.5hp 2 stroke mercury engine. No water is running out of the whole so the guy said its the water pump. was it hard to change the water pump? By the way do you know were I can get a manual for the engine? maybe on line somewhere?

Re: 1971 Mercury 7.5 HP Water Pump Problem

This is a great site for old mercs. Good Luck!

http://www.eastcoastmarineservice.com/marine_accesories.htm

Re: 1971 Mercury 7.5 HP Water Pump Problem

Well ive already changed my impeller and added the missing key the previous repair shop forgot to install but still just getting smoke from pee hole .All lines are clear as air flows freely through them ,any ideas ? mine is a 1974 so should be the same set-up.thanks

Re: 1971 Mercury 7.5 HP Water Pump Problem

OK. I have some experience with this.. first and for most. Take the lower unit off again.. Check to see your impeller isn't trashed again. if the little balls on the end of the impeller are gone, then get a new one (looking from the top down with the impeller laid flat you will see roundness on the ends of the fins). if that's good, then when check to see that your tube's are aligned correctly. Not always evident that they are connected. Then on the top if the motor head, check the 90 elbow for obstruction. If you have tosted an impeller before, then 99.8 percent of the time, your going to get some of the burned up plastic up the tube and caught in the flow somewhere. One last place to look, at the bottom of the cavitation plate. You may have a plugged intake screen.. Good luck. Hope it helps..

Re: 1971 Mercury 7.5 HP Water Pump Problem

If they left out the key did they also leave the face plate out. it is stainless steel and goes between the impeller and water pump cover. Will not pump much water with out this. You can test the pump by taking the lower unit off and placing it in a 5 gal pail of water. Use a drill to spin the drive shaft clockwise and run the pump. Put a couple foot piece of tubing in the pump outlet to make sure the pump will lift the water high enough. this will allow you to determine if it is the pump is working (make sure the intake is clear) If the pump works there is a blocked passage in the power head or inner exhaust manifold or water outlet line
On a 9.8 merc it takes a drill with a 1/2 inch chuck, possibly the drive shaft on a 7.5 has a diameter small enough to us a 3/8 drill.