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30 HP Mercury issues

Mike

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I've been having issues with my 30 HP oil injected merc for years. The issue is intermittent. Sometimes when running full throttle, the motor will just quit. I can get it started without issue, but then when I put it into gear and throttle up it dies. It runs fine in idle. I had to hobble back to the launch again. I replaced the fuel line last year. The carb was rebuilt by bass pro three years ago.
 

jagermeister

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Are there adjustment knobs on the carb for tweaking the fuel/air mix? Usually there's one for high speed and one for low speed (idle). Maybe it needs richened up a bit at high speed (more fuel less air).
 

Mike

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I've been reading up on this issue. It could be the primer bulb, fuel pump, fuel filter and s host of other problems. When I had it at bass pro, they couldn't duplicate the issue in the tank. What gets me is the problem doesn't happen every time.
 

Joel

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It sounds exactly like a carb issue I had with a motorcycle a few years ago. Took weeks of messing with it to figure it out but eventually I took the carb apart and cleaned it really good and the issue stopped. I tried lots of other crap first and every time I thought it was fixed it happened again. There were little tiny particles that were getting stuck in the needle jet when the RPMS were up. It wouldn't do it until the vibration of the motor at high RPMs mixed with sucking in lots of fuel quick caused one of those little chunks to get lodged in and then it would either lose power or shut down the motor completely. A few minutes later it would start right up and run fine.

I know that was a bike and you're talking about a boat. Also I am not a mechanic but from hours and hours of frustration that's what I learned and it sounds like it could be your problem.
 

jagermeister

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Keep in mind too that this new ethanol blended fuel is terrible for outboards and other small engines. Use stabil or some other type of fuel treatment. If this kind of fuel sits for any period of time it gums up in the tank... And in the fuel system of the engine.
 

hickslawns

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Keep in mind too that this new ethanol blended fuel is terrible for outboards and other small engines. Use stabil or some other type of fuel treatment. If this kind of fuel sits for any period of time it gums up in the tank... And in the fuel system of the engine.

Very true. Best thing that happened to small engine shops. Keeps them all busy. Joel brings up a valid point as well. Never a bad thing to change the fuel filter. They can look fine but be plugged. Adding an additional fuel filter isn't a terrible idea either. Wish I knew more about boat motors to help you out. Worked on plenty of other small engines.
 

Mike

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Definitely going to get a new fuel filter. It's looks like it's never been changed! I've always added marine grade Stability to my fuel.
 

"J"

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I've been reading up on this issue. It could be the primer bulb, fuel pump, fuel filter and s host of other problems. When I had it at bass pro, they couldn't duplicate the issue in the tank. What gets me is the problem doesn't happen every time.

Do you have the portable 5 gallon tank that just plugs into the motor? If so did you have the tank with the motor when bass pro worked on it? If not I'd be looking at he tank too see if hats an issue..... Ran fine for them without your tank but using your tank it doesn't run fine would lead me in that direction....
 

Mike

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Do you have the portable 5 gallon tank that just plugs into the motor? If so did you have the tank with the motor when bass pro worked on it? If not I'd be looking at he tank too see if hats an issue..... Ran fine for them without your tank but using your tank it doesn't run fine would lead me in that direction....

Good call J. This has crossed my mind as well.
 

"J"

Git Off My Lawn
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I've got Expedia de with the bigger outboards over the years and there's a website that I periodically go too for unusual problems that people on there can answer as well if you need it....
 

Mike

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I ran it this morning. No issues going out, but it did the same thing coming in. I can get it to run at full throttle if I continually pump the primer bulb. Air leak or bad fuel pump diaphragm?
 

"J"

Git Off My Lawn
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Replace the hose and clamps from the tank too the motor.... Primer bulb should be full after the initial pump up if any needed.... Also make sure the vent too the tank isn't plugged up creating a vacuum....
 

Mike

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New hose and connectors last year J. It seems to always happen on the way in. I'll check the tank next.
 

Mike

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It did the same thing today. We went to open it up on the larger part if the river. It was running fine at full throttle and then bam, it shut off as if someone pulled the emergency shut off switch. We sputtered back on low throttle for about ten minutes and then it just started running fine again.
 

hickslawns

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Ok. Let's analyze. I am thinking out loud. Basics first.

We need fuel, air, and fire.

Fuel lines replaced. Carb rebuilt 3 years ago. With ethanol mentioned, I wouldn't totally rule out the carb if it were my boat.

Air? Not sure I would think air filter if it starts right back up just fine.

Fire? Spark plugs and wires good? Once warmed up, I could see an issue here. I have heard of spark plugs which have hairline cracks barely visible to naked eye. Tough to tell with plug wires. Never hurts to replace them.

Ignition? Does it have points? I wouldn't think so given the year. I have had small engines in the 20hp range which are 2cyl engines. We have had coils go bad on a cylinder before. Sometimes they run fine at start up, but sporadically fire on one cylinder once warmed up when they are starting to go. Other times they just don't work and only fire on one cylinder. Could it be an intermittent deal where the coil is not working right once warmed up?

As stated, just thinking out loud. Not much to small engines so i am just trying to throw some things out for you to think about. Not trying to sound so simplistic, but when analyzing something I find it best to go back to the basics. I start ruling out things and narrowing down my possible problems. Hopefully it triggers something in your head you may have overlooked. As stated before, I don't know didley about marine engines. Internal combustion engines all share fuel/air/fire though.