Mercury 7.5HP Problem

[Postletown]

Hey Everyone, This is my first post in a long time but I've read this website for a while and its really helpful. I'm having a problem with my 7.5 mercury, I think it's from the 70's? Anyway, sometimes the motor will run great. It will idle, go into gear and back to idle just fine for a long time. Other times, it will start up and shut down at idle or when I try to go into gear. I recently replaced the fuel line and tank to eliminate that possibility. The other important bit of info is that the foam on the cover has been severely deteriorating and getting all over the inside of the motor (I've recently cleaned it up the best I could and took all of the remaining foam off. My thought is that the tiny pieces of foam have been clogging the carb. I am not very experienced at working with motors, but I'm learning as I go. Does this sound like a carb jet issue? Thanks in advance!

 

[racerone]

Get rid of that foam !-----------The foam would get into the reed valves and hold them open.----------Causes running problems.

 

[Postletown]

I did get rid of it, how do I clean the reed valves? Or is it too late? Is that what my problem sounds like? Thanks!

 

[merc850]

It's a 1975 era motor. You can check for open reed valves by running the motor and holding a piece of paper in front of the carb, if it blows away from the throat and fuel sprays on to it there's a stuck reed. Will it run while pumping the bulb? Have you replaced the fuel pump diaphragm?

 

[Postletown]

No, I haven't. And no it doesn't stay running long enough to pump the bulb. I will try the paper test for sure. The thing that gets me is that sometimes the motor will run great then this happens. Would this have anything to do with the carb itself? Is there a chance the particles from the foam are getting stuck in there then blowing out then getting stuck in there again?

 

[merc850]

The motor would never run if foam is plugging up the carb use a mirror and flashlight to look in carb, and check the spark using a timing light - this could be a coil problem; you are going to have to check all the systems to narrow down the problem.

 

[Postletown]

Ok, sounds like I need to take it to someone who knows what they're doing. Thanks for the info, I really appreciate it.

 

[Postletown]

Well, I have some updates and another question.....

I did not end up taking it to a shop, but I did some more fiddling. I cleaned the whole thing out and got rid of all the foam on the cover. I got all of the foam off of the inside and it is now pretty clean. I sprayed some carb cleaner in the carb as well. The paper test revealed no gas spraying onto the paper. The motor will now run, but only until the fuel that I manually pumped into the carb with the bulb burns up. If I continue pumping the bulb the motor will run and run forever. Is this a fuel pump issue? Where do I locate it on this engine and where can I get one? (And just a reminder, the fuel tank and fuel line are both brand new) Thanks again in advance!

 

[merc850]

Follow the fuel line from the bayonet fitting to the pump which should be on the side of the carb. There should also be a filter cover that is removable and cleanable; you can get the parts from a Merc dealer or here http://store.oldmercs.com/category_s/1801.htm

 

[Postletown]

Ok thanks! I thought that might be the fuel pump, but wasn't sure. It seems the only parts that are replaceable on it are the gaskets/diaphragm. Is that true? Either way, I ordered a kit that contains both. Thanks again!

 

[60sboater]

Yes,the pump is the left side of the carb. Make sure to get the diaphragms and gaskets back together in the correct order.

 

[Postletown]

I will do my best, lol. So, if this is my problem, is it correct to say that the seals aren't fully sealing it properly and air is getting in the fuel system?

 

[merc850]

Probably the diaphragm has stretched or the check valves aren't closing so the pump won't draw fuel.

 

[Postletown]

Ok, I replaced the fuel pump parts. It will idle great and it keeps getting fuel now. I think that part is fixed. Now, when I put it in gear it shuts down, but when I was calling it quits for the night and running the gas out with the fuel line disconnected I tried putting it in gear and it worked just fine. I tried this several times, didn't go into gear with fuel line connected, did go into gear with fuel line disconnected. Any idea what is going on here?

 

[Postletown]

After doing some research, it seems I am getting too much fuel. My thoughts are that I either need to check to make sure I installed the new fuel pump gaskets and diaphragm correctly, change the float and seat on the carb, or replace the fuel line connector inside the motor. I purchased a carb rebuild kit as well as the float and seat as well as the fuel line connector for a few bucks on ebay. We will see what happens after all of this. Hopefully I am on the right track.