Yamaha Enduro 2 Stoke 15HP Not Running too well?

[UFO]

I have the above motor which gets a slight judder to it every few seconds.


The motor is new to me and has been sitting (without fuel in the carby) for a couple of months and is now running on fresh fuel with the correct 50:1 mix.


Apart from the judder it runs fine at low and high revs and goes faster than what I want to go



As far as I am aware it is a 2007 model - Is this just an old engine, or should I be cleaning the carby etc?


Below is a link to a short video for it - Let it fully buffer as it appears my server is crap


https://www.thecruisingcat.com/index...-enduro-video/


Thanks in Advance

[sailormed]

Runs fine for me, it is a 2 stroke, so maybe skipping a cycle from time to time. I would not bother, leave it alone if that is the only point of concern.

[Thumbs Up]

Tough to diagnose. Could be running rich. Sometimes a main jet can erode (pretty common actually), If you do end up rebuilding the carb, order a new jet (doesn't come in the kit), or buy a fresh carb. There are several clone brands of these engines with cheap but identical parts.

[donradcliffe]

It is running a little rough, most likely a fuel problem. Could be a little water in the fuel, air leakage, or running rich. Does it smooth out at higher revs?

[flyingfin]

Do you put in a new NGK spark plug every year? And check the Yamaha manual to ensure you are running the right spark plug. Dont trust the kid at the auto parts store to give you the correct heat range plug for a 2 stroke

[Calaban-Alleria]

As others have said a new proper spark plug is a good place to start. (When I had a 2-stroke motorcycle I always carried a few spare plugs in my jacket pocket.) You may want to do a spark plug chop test to see how things are doing mixture wise. - Warm the engine, - install a fresh plug, - run 5 min or so at a constant rpm/load (the throttle opening determines which jet is functioning, - hit kill switch, - pull the plug and examine the electrode. If its burning well it should be the colour of well creamed coffee. If its lighter or shows and signs of eroding it too lean, Wet or oily well too rich. Could possibly be an air leak at a gasket that might be intermittent with vibration. Also if this is a engine that has reed valves you could pull the reed valve assembly and examine, making sure they lay flat and dont have any chips or cracks. Good luck.

[a64pilot]

With small carbs, there are usually two jets or circuits. Idle and main. Now there is no point where one cuts out and the other is completely in charge so to speak, but almost always much above idle, your on the main jet / circuit. The idle is still there, but it’s tiny compared to the main so it’s very much just simply overwhelmed.
Most of the time a dirty idle circuit will manifest itself as being difficult to idle and you can almost always make it much better by putting on some choke.
A main circuit manifests itself as being rough at any throttle much above idle, and again can often be made better with some choke.
Lean is usually a surging type of thing, won’t hold a steady RPM and as I said if you add choke it fixies it.
Rich often smokes more and “four strokes” meaning of course missing every other firing stroke, and the real clue is adding choke makes it worse.

Anytime a motor gets rough, it’s time for a simple carb cleaning, plugs can’t hurt, and while I have never seen a jet just wear out, it’s possible and your taking the thing out anyway, may as well put in a new one.


If you know how to read plugs, they can tell you a lot, certainly can tell you if your too rich or too lean.

[Scubaseas]

Sounds like secondary ignition issue to me. Follow #6 post above (kudos for good info). Probable it's a plug. Possible it's a wire which is part of the coil.



If not spark issue then look at fuel. As in open the carb and clean the jets.

[Boatyarddog]

Originally Posted by UFO

I have the above motor which gets a slight judder to it every few seconds.


The motor is new to me and has been sitting (without fuel in the carby) for a couple of months and is now running on fresh fuel with the correct 50:1 mix.


Apart from the judder it runs fine at low and high revs and goes faster than what I want to go



As far as I am aware it is a 2007 model - Is this just an old engine, or should I be cleaning the carby etc?


Below is a link to a short video for it - Let it fully buffer as it appears my server is crap


https://www.thecruisingcat.com/index...-enduro-video/


Thanks in Advance

Check compression, new plugs, then if okay. 110 compression, no less than 100
Clean Carbies.
SV Cloud Duster

[sailcrazy]

Following. We use the same O/B, bought new in 2010 in Manila. Because we rely on it so much, I am in the habit of just taking it to an O/B mechanic, have him drop the lower end and replace the water pump impeller, clean the carb, and put in new plugs every season before we resplash. Maybe overkill, but she starts on the first pull every time, and runs good through out the 6-mo season.

[Mike Banks]

That sounds like too much fuel--but it could also have been too lirttle fuel because of a partially blocked carby--almost as if the choke is stuck on.

I did not see any water from the cooling system either--just check to see if the impeller is able to circulate cooling water. These outboard engines are prone to blocking the water inlets with debris--and also the alloy inside the cooling chambers can oxidise and block the waterway as happened to mine, although mine was a smaller engine model.. Also check the thermostat.

Another problem can be the reed valves stuck with the gum from old petrol. They are behind the carburettor, one cleans them using a solvent. If they are not working the proper amount of fuel can not reach the engine cylinders.

I downloaded a workshop manual for mine--it was a big help.

[UFO]

Thanks for all the great advice - When I get a chance to bring it home I will get onto the items everyone highlighted.


I can not find a service manual online for it though, so if anyone has one I'd really appreciate a link to it

[UFO]

Originally Posted by donradcliffe

It is running a little rough, most likely a fuel problem. Could be a little water in the fuel, air leakage, or running rich. Does it smooth out at higher revs?

Only very slightly smoother at higher Revs

[HankOnthewater]

Originally Posted by UFO

Thanks for all the great advice - When I get a chance to bring it home I will get onto the items everyone highlighted.


I can not find a service manual online for it though, so if anyone has one I'd really appreciate a link to it

Have the same engine, similar vintage, have same issue at times, changing sparkplugs did not work for me. I would say 'jet' issue, stale fuel issue, deposits in carby issue, as 10-15 seconds at full throttle, seems to clear it.
I have the manual/service book what came with the engine, happy to scan that, but certainly it is not a workshop manual.
I have also a manual on CD of a previous 2 stoke 15 HP (not Enduro) at ~130 Mb, covering that outboard around 1997-2003.

[UFO]

Originally Posted by HankOnthewater

Have the same engine, similar vintage, have same issue at times, changing sparkplugs did not work for me. I would say 'jet' issue, stale fuel issue, deposits in carby issue, as 10-15 seconds at full throttle, seems to clear it.
I have the manual/service book what came with the engine, happy to scan that, but certainly it is not a workshop manual.
I have also a manual on CD of a previous 2 stoke 15 HP (not Enduro) at ~130 Mb, covering that outboard around 1997-2003.

Hi Hank,


Thanks for the offer - Scanning sounds like a lot of work, so I will try and find one online, but I may come back to you - Would only need the important parts.


I'll wait for a calm day and see if I can blow the cobwebs out at full throttle for a burst