Yamaha 01 F15 no power under load

[gnonya357]

Hey everyone, I hope someone can give me a hand with this one, motor starts fine, idles fine no problem shifting but here's the rub. No power it wont go any faster than maybe 5 mph on 14ft aluminum v hull problem started out of blue took boat out I was doing 21 mph one day then snail slow the next trip out. Some things I've done to the motor are: I cleaned the carb several times and a rebuild kit and no fix so than I replaced carb same problem nothing changed! fuel filters and fuel lines are in good shape, new bulb. I dropped the lower unit and checked the impeller its perfect. So that leads me to fire and compression, I checked spark and I was getting a faint blue spark when I put the plug against the block and pulled the rope. When the rain stops I got new plugs to put in and do a compression check. Anything I could be missing on carb maybe butterfly not opening all the way?.....Thanks

[Jason2tpa]

Diagnosing using mph as the primary indicator of performance is unreliable, just fyi. Too many variables having nothing to do with engine performance affect speed. Be that as it may, obviously the engine is not performing up to spec if you're used to running at 21mph and now only 5mph.

Monitoring rpms will lead you down a quicker path to diagnosing engine woes. Do you know what your rpms were at when running 21mph, as well as when running 5mph?

When you cleaned the carbs and installed new kit, did you also pull the 2 jets? These jets have such a small I.D., so it doesn't take much debris to clog them. Each one needs to be completely clear of debris. When you hold jet up to light you should be able to see through.

[gnonya357]

Sorry, no RPM gauge its just a small outboard tiller control on a aluminum Vhull jets were taking out and cleaned, when that didn't fix it I just put a new carb on last Saturday same issue.

[Jason2tpa]

Sorry, no RPM gauge its just a small outboard tiller control on a aluminum Vhull jets were taking out and cleaned, when that didn't fix it I just put a new carb on last Saturday same issue.

Gotcha. Safe to assume new carb has free and clear jets. Well since you can't monitor rpms, have you noticed a dramatic change of the way the engine sounds? With only 2 cylinders, if one or both were performing poorly I would think the audible difference compared to when performing optimally is easy to notice.

How about smoke? Notice more smoke than usual, and if so what color? Smell of burning or of fuel, more than usual?

What were the condition of plugs? Fouled, clean?

Btw, you can pickup an external tachometer for your engine. Inexpensive. It's a small digital readout that you can mount somewhere outside the engine. A wire connected to the digital readout snakes under the upper cowling and wraps around one of the spark plug wires. They are not always 100% accurate. But in the ballpark is better than no ballpark. Just a suggestion.

[TownsendsFJR1300]

Can you squeeze AND pump up the primer bulb when underway? Does it help?

The "new" carb, I assume is ANOTHER CARB, not a brand new, out of the box carb, correct?

As we don't know your model #, here's a parts diagram for your FUEL PUMP (or close to it):
http://www.boats.net/parts/search/Ya...UEL/parts.html

You may want to inspect that for beginnings of failure (torn, ripped, leaking diaphragm, etc)


As you only have one carb, if you can rig up a temporary fuel tank, (GRAVITY) direct to the carb, you'd eliminate most of the fuel system. I use a small lawn mower tank with an on/off valve, easily con*****ed, etc.

Just a side note, your issues DO sound like a clogged carb, especially the main jet. To confirm, it WAS pulled out and visually inspected???

The carb (part #10) : http://www.boats.net/parts/search/Ya...TOR/parts.html
looks like it may have an accelerator valve(extra fuel when nailing it).

*I may be wrong, someone else please chime in. There should be an orifice for that diaphragm, is that opening clear? Is that diaphragm un-damaged?



.

[rejesterd]

What you describe sounds like a cooling water issue, but I assume you're not seeing any overheat warnings. So that indicates that it's not a clog in the water inlet. Did you check the thermostat and thermoswitch? If those are both good, you should replace the CDI unit. If it was working fine one day then totally not fine the next, it could just be that the CDI went bad.

After that, I would check the engine oil level and the oil pressure. If the oil pressure is out-of-spec, check the oil pump to make sure it's clean. If oil pressure is fine, test the oil pressure switch. If that's working ok, that leads back to the CDI again.

Is the idle speed really steady or does it go up & down? I think that's another question that a tachometer will answer. Probably worth the money, because the tach will come in handy in troubleshooting other issues down the road.

[carlitos]

By any chance have you checked your prop and make sure that it is clear and does not have any foreign material wrapped on it and that it is not spinning on the shaft ?

[gnonya357]

I figured out my problem the butterfly wasn't opening all the way. One quick adjustment and she was running tip top...Thanks everyone!!