Mercury 7.5hp - Questions.....need answers!

[Platties]

Hi,

I just picked up a 7.5 hp Merc outboard, not been run for 10 years but very clean.

What plugs does it take?

How old is it, serial no 9423897?

Is it a 50:1 fuel/oil mix engine?

How many turns out from bottom do I set the idle screw to start with?

Are they any good?

Thanks for any help, It could be just the right outboard for us.

 

[QC]

Re: Mercury 7.5hp - Questions.....need answers!

Hey Platties. Let's see if we get some more action over here in the Mercury section. Good luck!!

 

[James R]

Re: Mercury 7.5hp - Questions.....need answers!

Can't be sure about the year. Possibly early 80s. 50:1 is correct.
Shoot some Marvel Mystery oil in each plug hole, turn the motor over and leave it to soak overnight. Check compressions. Should be close to even for both cylinders and above 100PSI.
Whilst doing this be sure to ground the plugs and this will enable a spark check.
If you have this then the next step is to check the shifting of the gearbox. Next drain the oil from the lower and check for water and metal particles in the oil. Pull the lower unit and replace the impeller. Fill with fresh oil.
Next clean the carb and check the float height settings. Replace the needle jet and seat if neccessary. Replace the gaskets and rebuild the fuel pump.
So now you can see the need for a Manual.
If you are serious about fixing this motor please get a manual.

 

[Platties]

Re: Mercury 7.5hp - Questions.....need answers!

Thanks James,

I've learned allot about this engine since my last post. I've installed a new impeller, new plugs, new oil in the bottom end and rebuilt the carb and fuel pump with a new seal kit. So she should run well,...........but she doesn't!

I've only run her up in a barrel. She starts ok, but fuel seems to come out of the little hole in the carb just by the air intake and gets sucked into the card, which makes her run ruff and stop. I adjusted the float, which helps, but as the needle valve has a spring on it, its hard the know where to set it? If I pump the bulb up too hard, fuel also squirts out of this hole?
She runs sort of ok, but then suddenly stops, for no apparent reason, and will not restart. I've been over all the electrical side, which there is not much off, cleaned all connections etc. Has anyone got any suggestions, they would be very welcome.

 

[Shatterpate]

Re: Mercury 7.5hp - Questions.....need answers!

I got the same problems, but i can start it every time again. All I need to do is pumping gas and she goes again for a few seconds. Did not replace the fuel pump yet, but took carb apart and seen that the little round black plastic inlay was not in its right position. So I replaced it and thought that was it, but no it was not.
Need help, what else should i do? Next I will get new fuel pump I guess...

 

[James R]

Re: Mercury 7.5hp - Questions.....need answers!

If fuel continues to come out of the carb when pumping the bulb the float needle is not sealing. You will need to replace the needle and the seat. The problem is that the seat is a press fit and will have to be carefully drilled out on a small drill press. The new seat can be epoxied in. The float heights will need adjusting. If you make a mistake the carb is toast.

 

[Shatterpate]

Re: Mercury 7.5hp - Questions.....need answers!

mhhhm I read a few time something about a needle, but when I took my carb apart, I didn't see a needle. You mean there should be a needle where that brass hollow thing is, which comes up from the float? I'm confused a bit...

Edit: Well if I pump really really hard, I manage to squeeze gas through the carbs little brass hollow thing, where the intake is.

 

[James R]

Re: Mercury 7.5hp - Questions.....need answers!

From what you have been saying you know very little about motors, carburetors in particular. There should be a needle seated in a brass jet inside the float chamber. The needle is operated by the float up and down action. If this needle does not seat correctly, when the float chamber is full, fuel will continue to feed and cause the motor to pull to much fuel into the cylinders.
A manual would be a good investment.
Wet string and bent nail servicing of outboards only leads to being stuck on the pond.