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Old 01-01-2020, 14:45   #31
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Re: Yamaha 15hp Enduro wont run - Please help!

The worst thing is you left the OB with gas in the carburetor one time too many and the carb is gummed up and unless you put in a sonicator and clean it. Change the plugs and you will be running around the marina in circles.
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Old 01-01-2020, 15:38   #32
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Re: Yamaha 15hp Enduro wont run - Please help!

I ordered a brand new carburetor off Amazon - confirmed its the correct one for the Enduro - $139 delivered, will be here Friday morning. I'll post back what happens when I install it. Could have gotten the same carb on ebay for $75 but had to be shipped from China and I can't wait 10 days.

I do think I could get the carb on it going with a better cleaning and I would wager the idle jet is the issue. But with several other big issues to be tackling this one needs the fastest / easiest fix possible.

All the posts and help here is just awesome!


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Old 01-01-2020, 20:27   #33
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Re: Yamaha 15hp Enduro wont run - Please help!

Hi, yes the manual states 1.5 turns out but that is for a new carb.
As a few hundred hours tick by, the brass jets and nozzles and the aeration tube become eroded by the fuel and small amounts of water transported by the ammonia in Tcw3 oil.
This enlarging enriches the mixture, to allow for this I usually start at 2.5 out, then go in 1/4 turn at a time to find the sweet spot where there is no bogging down when you blip the throttle from idle, and the motor does not sneeze at idle.
I'm sure you have seen that sandblasted effect on the brass parts, that is the erosion I mentioned.
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Old 02-01-2020, 12:29   #34
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Re: Yamaha 15hp Enduro wont run - Please help!

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Originally Posted by Tspringer View Post
THANK YOU for all the replies - great info and very helpful.

I am going to take the Yamaha apart again and do as suggested in this thread to clean the jets with care and really clean everything. If that does not do it - I will likely just buy a new carb, they are not crazy expensive.

I did pull both spark plugs prepared to replace them but they look new and have no carbon buildup. Given that the engine will initially fire and rev quickly but then dies I do not think spark is the issue - it's fuel. The idle jet having problems or the float not working correctly seem like likely suspects that I will check very close.


Terry
When it first fires, try getting it to run with about half choke. If it stays running, there's still some crap in the jet. May be extremely difficult to see, but it'll be there. Clean out with w very thin piece of wire and it should run.
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Old 02-01-2020, 12:53   #35
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Re: Yamaha 15hp Enduro wont run - Please help!

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I donít believe that exists even as a two stroke, itís achievable of course, if the manufacturers would put a two stroke on the same diet they did the modern four strokes, but I donít expect to see that. It seems that for the most part development of two strokes is at an end.

Unfortunately this seems to be all too true. Next plan is to rig a better bridle and lifting system for the outboard



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The HP per is most relevant, because it speaks to what is possible.
For instance the Yamaha 9.9 weighs the same as the 15, because itís the same motor of course, but the 15 is the highest HP they get out of that motor.

Suzuki chose to build 20 HP as the highest, itís likely had they chosen 15 as the max it would have weighed less than the Yamaha 15 two stroke.

Have seen that commonly in outboards. Difference I guess is the carburetion or is it a higher compression ratio?
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Old 02-01-2020, 12:59   #36
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Re: Yamaha 15hp Enduro wont run - Please help!

I dealt with a similar problem with a non-Enduro Yamaha 15 2stroke. As you can see, parts are readily available. Mine was the smallest of hole in the diaphragm in the fuel pump, and after getting the rebuild kit, it had also lost its firmness so I think it really wasn't functioning very well. Also found that after a period of time, some of the older fuel lines from tank to motor can collapse on the inner wall of the hose restricting fuel. The new lines and tanks aren't vented so that creates another problem. Mercury developed a device that goes inline from the tank to the motor that doesn't allow the pressurized fuel to be forced into the carb when either you have a new unvented tank, or you have left the vent on a vented tank closed, and the pressure really builds. If you are heading to the Bahamas, I would think about a new fuel line with the extra valve as a spare. The new hoses here are supposedly impervious to vapors leaching out, and better resistance to ethanoll. I wonder if gas in the Bahamas has ethanol in it or not, I imagine the US is their fuel supplier. You are right about keeping the Enduro, they don't make them like they used. I would rather have to be dealing with problems with a two stroke than the new four strokes. Good luck and give a heads up to how you ultimately resolve the issues.
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Old 02-01-2020, 13:08   #37
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Re: Yamaha 15hp Enduro wont run - Please help!

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Originally Posted by Tspringer View Post
I did pull both spark plugs prepared to replace them but they look new and have no carbon buildup. Given that the engine will initially fire and rev quickly but then dies I do not think spark is the issue - it's fuel. The idle jet having problems or the float not working correctly seem like likely suspects that I will check very close.


Terry

In your case I'll bet the problem is fuel based but I have had two small engines (old Mercury 3.3 2-stroke outboard and my log splitter with a Honda 4-stroke engine) that had these exact symptoms. Both would crank right up, run well for a few seconds then die. Even got them to run a few seconds longer playing with the choke so would have bet money the problem was the carbs.



After several cleanings I finally bought a new carb for the Honda engine but acted exactly the same. Sometime during the process I had pulled the plug, grounded it to the block and pulled the engine over and saw a nice, blue spark so was sure that wasn't the problem. Finally decided to install the new plug that was already sitting in my spares kit and that was it. Cranked immediately and ran without a sputter.


I had always thought that spark plugs were a go or no go, either worked or didn't. Was amazed to see one that would work fine for 10-20 seconds and quit. Anyone have any insights on this phenomenon I would love to hear it.
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Old 02-01-2020, 14:14   #38
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Re: Yamaha 15hp Enduro wont run - Please help!

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Have seen that commonly in outboards. Difference I guess is the carburetion or is it a higher compression ratio?
Itís been that way forever with aircraft engines, turbines anyway, the higher HP motors are just run at higher temps and speeds.

Modern outboards have gone that way, especially the computer controlled ones, The entire Mercury Verado line from 150 HP to I guess 350 HP is just two engines, 150 to I believe 200 is the four cylinder, then 225 to 350 is the six, with the computer being the difference, itís literally state of tune, no hard parts are different, but the computer controls rev limit and fuel of course and in the Verado the boost from the supercharger too.

Older engines itís usually the carburetor, maybe a restriction plate, and maybe ignition box
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Old 02-01-2020, 18:30   #39
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Re: Yamaha 15hp Enduro wont run - Please help!

Don't use wire! Mono-filament line works and won't scour the jet
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When it first fires, try getting it to run with about half choke. If it stays running, there's still some crap in the jet. May be extremely difficult to see, but it'll be there. Clean out with w very thin piece of wire and it should run.
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Old 06-01-2020, 08:14   #40
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Re: Yamaha 15hp Enduro wont run - Please help!

***UPDATE***

I got the new carburetor ordered off Amazon for $139 delivered. Right on the box it said "OEM Yamaha 15hp and had the correct part number.

It took me about 3 minutes to install it. I then pumped up the bulb until firm, pulled out the choke and yanked the starter cord. Fired immediately. Pushed in the choke, it idled perfectly. Took it for a test run - ran like new across the full rev range.

Fixed. New carb = the ticket!


Terry
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Old 06-01-2020, 13:46   #41
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Re: Yamaha 15hp Enduro wont run - Please help!

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Not a chance. I specifically wanted the 15hp Enduro model 2-stroke. These engines are built very tough and they only weigh about 78lb. The new 15hp 4-stroke engines are over 110lb. That weight difference is the difference between whether I can manhandle it around some or not. I also think the 2-stroke revs faster. No 4-stroke for me!

I can get a brand new complete carburetor assembly for less than $100.... that's what I am leaning toward doing. Get me running fast and then rebuild the old one at my leasure for a spare.


Terry

Exactly what I would do. Install the new one, rebuild the old, and you always have a working spare. You might only be able to find a rebuilt one, but that would be okay, too.


Be sure and check ebay.


Myself, I much prefer four strokes. But the Enduros are pretty good outboards, very popular with third world small boat fishermen.
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Old 06-01-2020, 13:49   #42
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Re: Yamaha 15hp Enduro wont run - Please help!

Quote:
Originally Posted by Tspringer View Post
***UPDATE***

I got the new carburetor ordered off Amazon for $139 delivered. Right on the box it said "OEM Yamaha 15hp and had the correct part number.

It took me about 3 minutes to install it. I then pumped up the bulb until firm, pulled out the choke and yanked the starter cord. Fired immediately. Pushed in the choke, it idled perfectly. Took it for a test run - ran like new across the full rev range.

Fixed. New carb = the ticket!


Terry
Now clean the old one, or if your unsure, have it cleaned. Best if you test it afterwards, but now you have a spare, do not get rid of the old one.

Hopefully this will never happen again, but odds are one day it will
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Old 06-01-2020, 15:48   #43
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Re: Yamaha 15hp Enduro wont run - Please help!

As mentioned earlier you may have an issue w the idle jet. Its always good to have a rebuild kit around with extra jets in it...then you can rebuild the old and have a spare. Nice thing about having a spare is you can do a quick swap then rebuild/clean the other one at your liesure.
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Old 07-01-2020, 07:24   #44
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Re: Yamaha 15hp Enduro wont run - Please help!

I had similar issues with a 15 Evinrude. First time the filter at the end of the dip tube in the tank was partially plugged (with a gel, my guess likely too much winter storage or oil) second time problem resolved by replacing the whole fuel line to the motor, dealer suspected a leak at suction end between the bulb and tank. After many hours spent working on & replacing motor stuff my motto has been to always go for the simplest thing first!
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Old 07-01-2020, 12:19   #45
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Re: Yamaha 15hp Enduro wont run - Please help!

Our Yamaha float was a close fit to the bowl and modern fuels caused the plastic to swell and scuff against the metal bowl. Could see the scuff marks. Carved away some plastic and problem went away.



I also second the points about finding the hidden Jets and side holes and cleaning with a tiny wire. Avoid ethanol fuels in the future for more reliable operation.
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