yamaha f150 txrd low on power

[wpowell323]

I have a f150 txrd that is off about 1000 rpm's at WOT. However it runs perfect and doesn't miss or sputter at any rpm. It use to run around 5800 and now only runs about 4800. The fuel pump in the vst locked up, so I put a new pump in the vst and cleaned the screen, when I put it in the lake it was off 1000 rpm's. Then I had the injectors cleaned. I replaced the fuel line and both fuel filters on the motor. I also checked the pickup in the fuel tank. I replaced the spark plugs, changed the gear lube and water pump and changed the engine oil and filter. I even went from a 17 pitch to a 15 pitch prop just to see and it still only wants to run around 4800. At WOT my butterfly's are open 87.4 degrees and the tps is at 4.086 according to the computer. I know the range on the TPS is up to 4.5, so should I adjust it so it at or very near 4.5 at wot? this is the only thing I can see on the computer that is not 100% within spec. Although I suspect at 4.086 it has already gone to full timing and such, but maybe not. I pulled the plugs and it seems to be running a little lean by the plugs. I have not checked fuel pressure, but it seems to have good power up to 4800 and pumping the bulb doesn't help and it doesn't speed up when you back off the throttle like some motors will when they are starved for fuel. Also the compression is fine on every cylinder. Any suggestions or what to look for would be greatly appreciated. I have access to YDS and am fairly knowledgeable with these motors, but this one has me stumped. Oh and the motor has 90 hours on it if that matters.

 

[Capt Ken]

Re: yamaha f150 txrd low on power

Check your VST pressure and don't mess with the TPS. Those readings have a +- tolerance.

 

[wpowell323]

Re: yamaha f150 txrd low on power

Pressure at the rail is 46-48 psi no matter the load or throttle position

 

[wpowell323]

Re: yamaha f150 txrd low on power

Pulled fuel sample and it clean and free of water

 

[Capt Ken]

Re: yamaha f150 txrd low on power

You did replace that small inline filter coming out of the VST tank?

 

[Capt Ken]

Re: yamaha f150 txrd low on power

Also, with the engine idling, listen at the back of the engine around the fuel pump. Do you hear a tapping like a valve tapping? If so, squeeze your primer bulb and see if the tapping stops. If so, then you have a fuel pump going out.

 

[wpowell323]

Re: yamaha f150 txrd low on power

You did replace that small inline filter coming out of the VST tank?

There is a metal like filter coming out of a line on top of the vst. But I thought that has something to do with vaccum. If not then I will order it and replace it as well. If u can confirm or maybe even give me a part number for the third filter that would be great

I replaced the canister filter and the filter from the low pressure to the vst. On the parts breakdown I didn't see any other fuel filters listed for this motor

Have not heard any tapping but I will listen closer and try to pump the bulb

 

[Capt Ken]

Re: yamaha f150 txrd low on power

I don't have the parts breakdown on this computer but earlier when I checked, it showed a filter on the outgoing line just above the VST that turned 90 degrees.

 

[wpowell323]

Re: yamaha f150 txrd low on power

I know there is a filter with 2 barbs on it, but that is on the incoming line from the upper low pressure pump. I just looked at every part diagram for a f150txrd on yamaha's parts lookup and I could only find 3 filters. Maybe the online schematic is different some places, but I didn't see any filter on the schematic or when I had it apart other than the three that I replaced, which is the main filter at the front, the filter in the VST and the filter before the VST from the low pressure pump. I know some models have a filter after the vst because it is like $60+ and customers get mad when you tell them one filter is that expensive. If you could locate the part number or tell me where to find it I would be very appreciative. At this point, unless I find that filter, I am going to remove the injectors and take them back to my buddy to have them cleaned and flowed again, just to see if maybe there was a little trash that somehow got trapped in a line and found the injectors.

I have fixed tons of these things and usually the things I have done clear it right up, of course the one I can't fix is the one I own, go figure.

 

[wpowell323]

Re: yamaha f150 txrd low on power

ok, so had time to mess with this hunk of junk again today. Checked low pressure pumps and they seem to be fine. Unhooked sensor on the top of butterfly's and the motor would not take any fuel and cut off, unhooked the IAC and didn't see much difference in the way it runs or crank, although when I cut the key off I can hear it close. Unhooked the other sensor on the top of the intake and with the motor running the motor cut off, but when it restarted it the motor ran fine and didn't seem to lose any power, it may have even gained a little, but it was virtually the same. So all that was inconclusive, but maybe someone reading can make sense of it

The one thing I have noticed is the fuel level in the front main filter is about 1 inch from the top, basically at the bottom edge of the element. This may be normal, but I have seen others that always seem to stay full. You can pump it full with the bulb, but once you crank the motor, it returns to about 1 inch from full. I have removed the filter and checked the seal and spring and all seems to be fine, but again maybe someone can put some insight into if this is correct or not.

 

[Bamaman1]

Re: yamaha f150 txrd low on power

You seem to be very technically capable. I'm sorry you're not getting more feedback on your motor.

My F150 has been trouble free, and I only know about Yamaha 115 hp 2 stroke motors.

Join BBCBoards.net, which is the bass boat website. Sign in to the Yamaha Motor section and do a short essay on what measures you've taken. They have some excellent outboard mechanics watching those sights that may be of help.

Once you diagnose your problem, it'll probably be something relatively simple to fix. The F150's are very reliable motors.