2000 Mercury 15 dingy motor

[pwmullins]

My dingy motor, standard Mercury 15, will start on first pull , power up on plane but when it runs for a few minutes it starts pulsating and won't reach full power then finally quits. Starts again, but will only run at low rpm's .

I rebuilt carb 3 months ago and it ran really good for a while. This just started. Use non ethanol gas, new gas line, old tank, old fittings. Feels like it's not getting enough fuel or there's an air leak.

Any other thoughts?

[a64pilot]

Fuel pump or possibly the vent on the tank being clogged, tank valve easy to check, open the filler cap and if it runs fine, then maybe you found your problem.
Usually a bad fuel pump, you can keep the engine running by pumping the squeeze bulb, in effect you became the fuel pump, usually.
It could even be the coil pack breaking down and not working when hot, or as bizarre as this sounds even plugs

[pwmullins]

Thanks, plugs are new, installed a new diaphram in fuel pump when I rebuilt carb. Will check out other suggestions.

[pwmullins]

Checked out suggestions from Moderator and still no luck. Ran motor on float dock for 10 to 15 min. at full throttle. Engine didn't appear to get to full rpm's. Tried adjusting the needle jet according to the manual; turn clockwise till it seats, then counter clockwise 1.5 turns and adjust from there.

Motor starts easily and idles and runs at low rpm's excellent, but when I get it up on plane it starts to bog down. Feels and sounds like it its loading up and running rich. My next move is to take carb apart and clean out, but it was rebuilt 3 months ago and I haven't run it much since then.

Any suggestions would be appreciated.

[TMT2]

I have a late model Yamaha 25 HP 4-Stroke on our RIB that was doing the same thing...did all you mentioned...Called Yamaha - they suggested a "sonic" cleaning by a certified dealer/service tech ($300). Bought a new carb ($240) - ran great! Took the old carb apart and cleaned all fuel pathways (completely thru) with a single gauge copper wire (1-strand) and carb cleaner. Tried the old carb - ran like a top. Lesson learned...may not be your problem - but worth a try to save $$$?

TMT 2
SV Take Me There!
Gulfstar M53 Ketch

[captjcook]

Inline filter? Seems like starvation, maybe needle/seat sticking or fouled, not allowing full flow...

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[Cheechako]

My 15 HP Yamaha did that... bad main bearing..

[a64pilot]

Originally Posted by Cheechako

My 15 HP Yamaha did that... bad main bearing..

Could be the crank seal too, but I hope not.
The mixture screw that you can adjust on a carburetor, should only adjust the low speed portion of the carb, once much above idle, you should be on the main jet and any mixture adjustments should require re-jetting.
Did you try manually pumping the squeeze bulb when she started to die? Often you can confirm fuel starvation that way.

[pwmullins]

Thanks for all the suggestions...I pumped the bulb while under full power with no effect. Looks like I'll take the carb apart and try cleaning all the jets and replace the float.

[pwmullins]

Thanks for all your suggestions and a great thanks to TMT2. I dismantled the carb and used a thin copper wire to check out all the jets. All were clear until I got to the breather jet on the bottom of the carb. When I ran the wire through it, a piece of junk came out and I surmised that the carb breather tube had been clogged. Put carb back on, ran out to the waterway and it has never run better. Thanks for the tip.

[TMT2]

Happy to help and save some $$$!

TMT2

[pwmullins]

Well, I thought I had the problem solved...ran the engine at full power and dingy on plane for over 20 minutes and it ran perfectly. Later in the day took it back out and ran at low power for 15 min. through some creeks, then crossed over the AICW and brought it up on plane. Ran for about 5 min. then it went into the fuel starvation mode and shut down. Had to fully choke the engine to get back to the dock. The good news is that we made it.

My last step in this process is to drain the fuel tank and see if there is any debris in the bottom that may be getting picked up.....it is a rather old fuel tank and I ran ethanol fuel in it years ago. Maybe some of it has broken down and is clogging up the intake?

[a64pilot]

If you find bits and pieces in the carb that look a little like black sand, it could be from your fuel line.

[TMT2]

If you ran ethanol in it and haven't cleaned all fuel passages in the carb since (a good soaking with MEK)...it's likely still gummed up...the debris is an additional factor -definitely clean the tank but disassemble and soak/blow out that carb again...IMHO.

[pwmullins]

O.K., this is my last post on this subject. I just took the dingy out and it ran great until I lowered the throttle to idle and then it died. Started right back up though and I motored back through the no wake zone to my slip. My final thought is that I have too much oil mixture in the fuel tank making it run too rich, but for now, I'll just live with it.

Thanks for all your suggestions.