1985 7.5 Merc Outboard Revving up Suddenly...

Hi guys,

I've been running a 7.5 HP 1985 Merc outboard on my sailboat all summer. It's seen pretty heavy use (2x week, min). Over the summer it has gradually getting tougher to keep it idling without stalling. The problem was mitigated somewhat when I started putting premium gas in it, but it would still stall out at low revs when in gear.

I changed the lower unit oil this year, and the spark-plugs. Someone suggested it might be that the carburetor needed cleaning. I got a can of carb cleaner and gave it a light spray.

Since then, the engine still has trouble idling, but now, when in gear it has a troubling tendency to suddenly rev up and then down again without any changes to the throttle. I can't be sure, but these higher revs do not seem to be translating into any additional power.

Finally, it seems I've lost all ability to reverse.

Any suggestions? Ideas?

Thanks a bunch

Peter

Re: 1985 7.5 Merc Outboard Revving up Suddenly...

Very well could be a dirty carb. Just spraying some cleaner in the throat won't clean it. The fuel pump and filters could be getting funky as well.

Re: 1985 7.5 Merc Outboard Revving up Suddenly...

Thanks, bob.

Is there a step-by-step guide published online that you're aware that could walk me through the steps required to clean the carb properly and clean/replace the fuel pump and filters?

cheers

Peter

Re: 1985 7.5 Merc Outboard Revving up Suddenly...

PeterSM said:

Thanks, bob.

Is there a step-by-step guide published online that you're aware that could walk me through the steps required to clean the carb properly and clean/replace the fuel pump and filters?

cheers

Peter

Click to expand...

Not sure on that year, I have a '70 model. But if you have mechanical ability just a picture is worth a thousand words.

Go to this link and fill in your info:
http://www.crowleymarine.com/parts.cfm
You'll want your serial number off your motor.
They used a couple different carbs on those motors.
Taking them apart and cleaning them is pretty simple. Ditto with the fuel pump.

Also check your fuel line.
Many times if the motor is running real lean or starving it will increase in rpms, but not power.

Re: 1985 7.5 Merc Outboard Revving up Suddenly...

Thanks, I will check the fuel line. By running lean do you mean the air/gasoline mixture, or the gasoline/oil mixture.

Thanks so much for the info!

cheers

Peter

Re: 1985 7.5 Merc Outboard Revving up Suddenly...

PeterSM said:

Thanks, I will check the fuel line. By running lean do you mean the air/gasoline mixture, or the gasoline/oil mixture.

Thanks so much for the info!

cheers

Peter

Click to expand...

Air gas. Gas oil stays the same. 50-1