2003 Merc 40 hp Loses Power and RPM

[Scallen2112]

Hi everyone. I started with search and may not have been using the right words, but I could not find the answer.

I have a 2003 40 HP Merc 2 stroke on a Tracker Panfish. The motor has been doing two things. First is it has been very hard to start. It takes up to 20 min of fiddling to get it going. After it starts the first time and runs for a few minutes, it cranks right up the rest of the day.

Secondly, on the last two trips, the motor has run fine for a few minutes, then suddenly loses power. The RPMs drop to about a third at full throttle and will not come back up. It will move along fine, but slow, and every once in a while it will rev back up on its own for a second. When I push in the key (choke?) it will rev back up for a second or two before dropping again. It still starts fine after the first time, and I can not detect any missing or sputtering.

I found this video on YouTube on cleaning the carbs that seemed to work for him:

2005 Mercury 50 hp 2 stroke engine (clean carbs) - YouTube

I did notice he had nothing about removing the jets or adjusting the floats as I have noticed on other threads here. I was hoping to get opinions on how to proceed. Should I give this a try? Is there anything else I should do when cleaning the carbs that is not in this video? Thanks for the help.

 

[racerone]

Re: 2003 Merc 40 hp Loses Power and RPM

Water in the fuel ?-------Is the motor overheating by chance ? ---Has the waterpump been changed ?------Oil injection verified to be working properly ?-----Have you checked fuel lines and fuel pick-up tube in the tank?-----I often see the pick-up in cheap plastic tanks cracked / split / deteriorated.------Inspection and cleaning of carburetors is fairly easy.-Floats rarely need to be adjusted.

 

[Scallen2112]

Re: 2003 Merc 40 hp Loses Power and RPM

Racerone - thanks for replying

The tank was recently drained and new gas put in with treatment.

The motor is not overheating and it is spitting water fine.

I don't know how to verify the oil, but no warning alarms are going off and it will run well - just at reduced power and rpm.

The lines are new and the bulb stays pumped hard. The pickup may be a problem as it needed more than half a tank to run before this started happening, but it was doing this with the tank completely full.

 

[racerone]

Re: 2003 Merc 40 hp Loses Power and RPM

Oil warning on some motors goes off when tank is low.---If system is not working properly the oil level does not go down.-----I would borrow another tank for a test run.---Having to use the enricher ( choke ) also indicates a fuel problem.

 

[BatDaddy1887]

Re: 2003 Merc 40 hp Loses Power and RPM

Also want to make sure you have good rubber in the fuel pump. It's also a good idea to use Seafoam or Quickcleen every other tankful to keep those carbs spotless.

 

[Scallen2112]

Re: 2003 Merc 40 hp Loses Power and RPM

Well well....I may not have to rebuild them at all. I started taking it apart and found that the fuel filter was packed full what is left of the inside of the fuel line. So, first I'm going to replace the filter and the line and see if that solves the problem before I tear into the carbs. I figured it had to be a fuel delivery problem because it revved when the enricher was pushed in.

 

[MH Hawker]

Re: 2003 Merc 40 hp Loses Power and RPM

I would say you found the problem.

 

[Scallen2112]

Re: 2003 Merc 40 hp Loses Power and RPM

Yep. Replaced the hose from the tank, new fuel filter, pulled and cleaned out all the hoses in the engine. It cranked right up and revved fine in the driveway. I'll take it to the lake in the morning and see how it runs, but I expect it will be fine. I cut open the old tank line, and except for a few little pieces, the liner in the old line was completely disintegrated and gone. I will take y'alls advice and replace the diaphragm in the pump. I didn't have to take the carbs apart, so I will keep the kits for a future date. I'll also pull the new filter after running it tomorrow and see if it has trapped any more debris that may have been in the pump. Thanks for the advice.

 

[oldman570]

Re: 2003 Merc 40 hp Loses Power and RPM

It sounds like the main trouble is the ethanol fuel has destroyed the old fuel line and can do so to the fuel pump diaphragm. when replacing any rubber fuel lines or parts be sure to use ones that are ethanol resistant. The other option would be to do a search of gas stations that sell non ethanol fuel nearby. A search at "pure-gas.org" will get you locations nearby for use in you motor.
JMO
Oldman570

 

[Scallen2112]

Re: 2003 Merc 40 hp Loses Power and RPM

It sounds like the main trouble is the ethanol fuel has destroyed the old fuel line and can do so to the fuel pump diaphragm. when replacing any rubber fuel lines or parts be sure to use ones that are ethanol resistant. The other option would be to do a search of gas stations that sell non ethanol fuel nearby. A search at "pure-gas.org" will get you locations nearby for use in you motor.
JMO
Oldman570

+

Thank you for letting me know about pure gas. org. The ethanol was absolutely the core problem.

My first fix of just replacing the main line and filter was not enough. It ran for a minute and went right back to doing the same thing. In the end, I had to drain and remove the tank to wash all the grit that was left from the deteriorated fuel line, rebuild the fuel pump, and rebuild all three carbs. The ethanol has disintegrated the liner in that main line to the point that nothing was left of it. It was all through the pump and lines in the form of plastic amber colored sand. Some had broken down enough to get through the filter and gum the carbs up with a carbon residue unlike anything I have seen before. It was caked up and looked almost like it was trying to turn back into plastic.

Lesson learned - as long as I can find "recreational fuel" somewhere, there will never again be any ethanol in the tank. I'm also going to send a letter to all my representatives detailing all the problems this junk has caused me and asking them to repeal the stupid mandate that we all have corn in our tanks.