Help Please - 50 HP 4 stroke Merc

[kbkrause]

50 hp merc 4 stroke

Took out my boat a while back and it wouldnt run well under load. High rev idle was fine but as soon as it was in gear it didnt run well. So on land I realized I didnt have a plug in all the way from when I winterized it. So tightened up the plug and I thought I'd be alright. Checked it on land and it ran well at idle and while in gear. Went out on Sat filled up the tank and put in a can of Seafoam and had the same problem. I couldnt get over 2800 rpms.

Any ideas?

[Damark Marine]

This is a tough one & could really use a bit more info, but I realize you would have added it if you had it. Stick to cking the basics good hot spark on all cyls, compression, fuel system good & tight plenty of flow & pressure.

If you find trouble we can go from there. Also is this a carb engine or EFI? serial #?

[kbkrause]

Sn: 06836607
1999
ELPT 4s

[spendit]

Do you have any alarms going off - oil pressure low.......2800RPM sounds like it is in gardian mode - good water stream coming out, might be getting too hot?

Pull all the plugs make sure they are working properly, run it in a tank of water or ears with cover off - look for head gasket leaks........

[Rooster Cogburn]

KB,

This is from way out in left field, but maybe worth mentioning....I'm wondering if it was possible the position of your backed-out spark plug could have caused your ignition coil output to increase, inturn damaging the secondary windings in your coil.

When secondary windings go you will get what seems like normal operation at low rpm's, but when you increase speed it tends to flood out.

It may seem far fetched, but if you run out of things to try...

[SabikiRig]

50 hp merc 4 stroke

Took out my boat a while back and it wouldnt run well under load. High rev idle was fine but as soon as it was in gear it didnt run well. So on land I realized I didnt have a plug in all the way from when I winterized it. So tightened up the plug and I thought I'd be alright. Checked it on land and it ran well at idle and while in gear. Went out on Sat filled up the tank and put in a can of Seafoam and had the same problem. I couldnt get over 2800 rpms.

Any ideas?

Seafoam is a great fuel treatment but, do not rely on it to magically resolve problems like this.

A friend of mine had similar issues with a (carb) 40 Merc 4 stroke. After he had the carbs adjusted (syncronized) the problem went away.

[b2theill]

carbs on those motors can be a problem. if you have never had a tune up/ sync and link, i would recommend it now. alot of time the balancing needs to be adjusted, especially a motor as old as yours. make sure you are hitting on all 4 cylinders too. darn yama-mercs....
best of luck