Intermittent power loss on F150 four stroke

[smooth37909]

Hello everyone. I am new to the forum. I hope that you can help me with a problem, lol.

I have a 2005 Century 1801 center console with a Yamaha F150TXRD four stroke. The motor has run like a champ until this year. Last year we were unable to use the boat due to personal reasons. My son and I got on the lake this Spring just to get out and get ready for the Summer. The motor started flawlessly. Initiated full throttle and it barely hit maybe 2,000 rpms. It was a huge disappointment. So, we came home and hooked it up to the hose. The temperature alarm went off. Since we had not run it last year, I figured we had a bad impeller. I removed the impeller and the plastic housing showed signs of melting. I replaced the impeller, the housing, and the thermostat. I replaced the spark plugs and the changed the oil and filter. We got a good run on the water at home; no overheating. We went out on the water today and the motor was intermittent at best. Sometimes we could get full throttle and rpms, and other times we could only get less than 2,000 rpms. We tried multiple scenarios to try to figure out if one caused the problem consistently. No luck. The engine is pissing strong and no overheat warnings. We just filled the tank with gas a few months ago and I always add Stabil Marine. The fuel filter shows no evidence of water (the float is at the bottom). I poured out the gas in the filter chamber and it is clear and smells fine. The air intake is clean.

So, I am a at a loss here. I am very comfortable working on cars and boats. I maintain all my vehicles. I appreciate any advice so my son and I can be on the water a lot this Summer.

 

[Fishhead-1]

You can check fuel pressure, but as the boat was laid up for the year I have a feeling your going to be removing and cleaning out the vst chamber and filter on the electric pump. You didn't say you had a miss like injectors. Plenty in this forum about vst.

 

[smooth37909]

Thanks Fishhead. I have done some looking around and I will tackle the VST next.

 

[smooth37909]

Okay. I replaced the fuel pump filter inside the VST. It was a huge pain since it had never been done before. I got everything all put back together but now the engine will not start. It cranks, but nothing else. I know that having drained the chamber with the fuel pump needs to be filled, but the low pressure pump does not seem to be filling the VST chamber. The lines in and out of the low pressure pump are dry. The small clear chamber with the water indicator is full of gas and there is no water in it. I am at a loss here. And yes, there is fuel in the tank.

 

[rejesterd]

If you open the gas cap on the tank after it's been sitting outside for a while, do you hear any pressure being released? It's possible you have a venting problem. Also, what happens if you leave the gas cap off and then pump the bulb? If the line going into the fuel pump is still dry, then look no further downstream than the fuel pump.

Also, if you find that you don't have a venting problem but the fuel pump outlet line is still dry, I would definitely check the fuel pump itself.. if something looks wrong with the diaphragm inside, I would drain the engine oil to make sure there's no fuel in there before you run it again.

 

[smooth37909]

It does not have a bulb (as far as I can tell). I suspected a fuel vent problem early on and even with the cap removed it ran rough.

 

[rejesterd]

hm.. it always ran ok without a primer bulb? I would install one to maybe help the low pressure pump prime the system.

 

[smooth37909]

It has always run fantastic till this year. Is there a way to prime the low pressure pump without a bulb? Btw, it is a four stroke.

 

[rejesterd]

The only other way I can think of is using another pump.

I would get the bulb assembly. It's very inexpensive and I actually don't know anyone who doesn't have one.

 

[smooth37909]

I'll be John Brown. I found a bulb. Pumped it up and heard the VST filling with gas. She started no problem. Gonna do a lake test tomorrow. Btw, the VST filter on the fuel pump was maybe 40% occluded. I hope this does the trick.

 

[rejesterd]

Cool. Yeah, maybe that 40% is where your power went.

 

[smooth37909]

Just got back from the lake and the motor ran great. I am so relieved now.