TOPIC: Merc 1150 issue

Hello i recently bought a boat that has the Merc 1150 thunderbolt on it. Issue i am having is it runs awesome for about 10 min then when going at WOT it is surging from 4500 to 2000 and back up then just looses all power other then a trolling speed then i can hit the power again and it will get up and just sit right back down i have replaced all fuel lines/filter new gas tank. The engine did sit for a year. I am at a stop loss here. Was reffered to this site via a Youtube video

I'm far from an expert, but it could be fuel pump, or a vent. A portable tank would answer the vent issue. If the pump hasn't been seen to in a while, that would also be an issue.

Will

Agreed with the above, Make sure the tank is vented (portable or otherwise). Else, the motor will create a vacuum in the tank by drawing out the gas to the point where the fuel pump can’t overcome the vacuum. Then when you lay off the throttle, the vacuum abates to more or less of a degree depending on how well the tank is sealed. Throttle back up and depending on how much vacuum was left on the tank the symptoms will reappear immediately or gradually.

I worked for an hour out on the water trying to figure out what the heck was up. I moved my tank out of the way and heard a slight hiss, and realized I had not opened the tank vent. Opened it, heard a rush of air into the tank, and presto! All better.

Failing that, next stop would be servicing the fuel pump.

check the pin in the male fuel connector if it is to short it will cause that problem.

Ill bet that's my issue thanks my tank does have a vent and i closed it off this is my first outboard engine so never had to deal with portable tanks. I will give that a try it does have a vent thanks guys i will give that a test then service the fuel pump if that doesn't do the trick.
peterstransky wrote:

Agreed with the above, Make sure the tank is vented (portable or otherwise). Else, the motor will create a vacuum in the tank by drawing out the gas to the point where the fuel pump can’t overcome the vacuum. Then when you lay off the throttle, the vacuum abates to more or less of a degree depending on how well the tank is sealed. Throttle back up and depending on how much vacuum was left on the tank the symptoms will reappear immediately or gradually.

I worked for an hour out on the water trying to figure out what the heck was up. I moved my tank out of the way and heard a slight hiss, and realized I had not opened the tank vent. Opened it, heard a rush of air into the tank, and presto! All better.

Failing that, next stop would be servicing the fuel pump.

wildturk,

WELCOME ABOARD.

yours, satx

So took the boat out today and the vent was the issue vented the tank and she ran like never before.... Thanks all.