Can't get full rpm's

[blazzinbird]

2000 sun tracker 18' party barge
75 hp tracker motor 2 cycle

Motor question....


So last week I brought up the question as to why all of a sudden our pontoon wouldn't get above 4200 rpm's. I came to the conclusion that It was due to the fact over to many people, and the Bimini top was up acting like a parachute.

Move to today, 2 adults and 1 child not to loaded down no top up. We got 4400 rpm's at WOT. Then I let my friend drive and I sat in the back, that's when I noticed some stuff. At higher rpm's the boat was surging, it acted like it wanted to go faster but couldn't. The primer bulb wasn't hard at this point.

I now wonder if the motor isn't starving at higher rpm's. Wonder if it could be a clogged fuel filter, or maybe the fuel pump is starting to get weak on up. Or maybe a spark issue.

What would anyone here suggest on where to start?

 

[Silvertip]

You are wondering rather than diagnosing. To run properly the engine needs fuel, air and spark and all needs to happen at the appropriate time. So start with the very basic things.
1) You said the primer bulb dis not stay hard. Well -- it not supposed to. You squeeze the bulb to force fuel into the carb for initial starts. Once started, fuel is "drawn" through the primer bulb not "forced" through it. Suck on an empty soda bottle to grasp this concept.
2) When bogging or surging starts, squeeze the primer bulb. If nothing changes you proved the fuel pump is NOT the issue. If the surging stops, the fuel pump MAY be the issue.
3) When were the plugs changed last? Inspect them!~ Wet? Black/sooty? Clean and tan colored.
4) What RPM did the engine turn before this problem showed up?
5) If the fuel filter had not been changed in the recent past, change it. It is not a budget buster.
6) Are you certain the engine is running on all cylinders? Do a spark test. A compression test would also help identify a weak cylinder(s)

 

[Scott Danforth]

Is your tank vent open?

 

[blazzinbird]

You are wondering rather than diagnosing. To run properly the engine needs fuel, air and spark and all needs to happen at the appropriate time. So start with the very basic things.
1) You said the primer bulb dis not stay hard. Well -- it not supposed to. You squeeze the bulb to force fuel into the carb for initial starts. Once started, fuel is "drawn" through the primer bulb not "forced" through it. Suck on an empty soda bottle to grasp this concept.
2) When bogging or surging starts, squeeze the primer bulb. If nothing changes you proved the fuel pump is NOT the issue. If the surging stops, the fuel pump MAY be the issue.
3) When were the plugs changed last? Inspect them!~ Wet? Black/sooty? Clean and tan colored.
4) What RPM did the engine turn before this problem showed up?
5) If the fuel filter had not been changed in the recent past, change it. It is not a budget buster.
6) Are you certain the engine is running on all cylinders? Do a spark test. A compression test would also help identify a weak cylinder(s)

The day we went on a test drive with the boat it turned over 5k rpm's

Plugs looked like good maybe a little wet...

I did mess up with the vent valve, our first day out I ran it all day with it closed. Was never told to crack it open.

 

[blazzinbird]

So here is my update...

This was more than likley all my fault. I used cheap gas from caseys in the tank, so I siphoned that all out and put high grade 93 octane in there.. The motor ran the same for about 20 mins then it jumped up 1000 rpm's. My guess is once all the fuel was out of the fuel lines and carbs.

 

[Silvertip]

Cheap gas was not the problem and 93 octane did nothing to help. Old gas or water was probably the problem and getting rid of it cleared the issue. Higher octane does not create more power. It retards detonation and unless the engine has a knock sensor and can automatically adjust ignition timing, you will not see an increase in power (but you will see a lightening of your wallet). Or the fuel system had some crud in it that suddenly was digested and the engine got healthy again.