150 mercuiser motor problem

[pizzaman_288]

we have a 150hp mercuiser and when we were at the gorge last week something happened with the motor it is only giving 2000-2200 rpms when under way and if you give it more gas the motor will start to stall out and you have to keep it at about 1/2 throttle any ideas on what to try when it sits at idle the motor runs fine and the rpms will go up with the more gas you give it but when you put it in gear and start to go rpms go up and then when you hit about 1/2 way on the throttle it stays at 2000rpms and if you give it more gas the motor will start to stall out any help would be great weve put a can of seafoam through it and are looking at giving it a tune up so any help on what to check would be great thanks

 

[lowe1648mt]

Try looking at the fuel filters. There is one inline before the carb. And one at the inlet on the carb. The one before the carb looks like an oil filter. The one on the carb looks like a large nut that the fuel line goes into.
If it's not either filter pluged, you may have to clean the carb.
There is some times a screen on the fuel tank pick-up. it can plug. It will unscrew from the tank. Then lift it out. Also on the top of the tank, there is a pipe nipple for the fuel line to hook to. It is a check valve. It may be partially pluged.
If you want to eliminate the fuel tank systen fom the possible problems, hook the motor to an outboard fuel tank. If it runs good, proplem is in the tank system. If it runs poorly still, look to the filters or carb. The oil in the fuel ( if it's from a 2 cycle ) will not cause harm if only used for a short time.

 

[pizzaman_288]

we have it hooked up to an external tank next to the motor and it has fresh gas in it so i know the tank is not the problem what kind of carb cleaner would you reccomend we use to help clean the carbs

 

[Master Chief]

So it will rev up in neutral (no load) without any problems? The fuel system would be were I would look first, lots of small orifaces that can clog up pretty easily inside a carb. If you have a pressure tester and the correct fitting testing the fuel pressure before the filters and after can give you a really good indication of a clogged fiter, once that is ruled out, I would not try to clean the carb while it is on the motor with a fuel system cleaner, generally they are good as a preventative maintenance but once something has a clog there is no way for the cleaner to get to the clog. I would just rebuild the carb, then re-test. If that does not fix it I would suspect bad coil or ignition system, under no load situation (neutral) the coil has no problem jumping spark plug gaps and igniting mixture, once a load is put on it adding a load plus extra fuel and air along with more turbulance in the combustion chamber (higher velocity air movement) can cause the spark to not have enough power to jump the gap and ignite the mixture. I am pretty confident with a little time you will have it back up and running right.

 

[lowe1648mt]

Thank You Master Cheif. All very good info.
What I would like to get with this type of question is all the info you can give. It's like playing detective. Your 150 I.O. , is it new?, Have you been running it earlier this season or is this the first time? When was it last serviced, and by a dealer or did you do it?
The more info we as a group have, the easier it is to diagnose. Some 3.0 liter Mercs needed a carb clean stright from the factory. They had what looked like sand in the carb. no amount of carb cleaner would ever do the job. Carb cleaners only remove "varnish" from a fuel system. Real clean means - Remove it from the boat, dissasemble,spray with carb cleaner or soak in same, and then blow out with an air hose. Then comes the hard part. Reassemble, adjust the float height setting and any adjusting screws that have been moved . Carbs ar best cleaned by some one that is trained and experienced. I don't like to mess with them. If you feel comfortable, then go for it. If not, take it to a shop some where. I prefer a Merc dealer as it is not an auto carb. They are different.

 

[pizzaman_288]

no its not new i believe its a 1968 or something like that im not sure though the motor its self hasnt been serviced that i know of we had the lower unit rebuilt about a month ago no its not the first time weve used it im thinking a good carb cleaning is in order

 

[lowe1648mt]

150 merc I.O.

no its not new i believe its a 1968 or something like that im not sure though the motor its self hasnt been serviced that i know of we had the lower unit rebuilt about a month ago no its not the first time weve used it im thinking a good carb cleaning is in order

Be sure to replace the fuel filter before you run it agin. If it does not have a fuel filter inline, have one put in when the carb job is done. Otherwise the carb may just plug up again.
Not familiar with Mercs that old. Back then I was working on OMC products ang going into the Army.