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Old 22-01-2018, 07:40   #1
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New 8hp Yamaha enduro runs poor

Bought a BRAND NEW 8hp Yamaha Enduro last spring. The shop ran it and gave it to me. I stored it on the boat for 8 months before running it.

Iím following the breakin schedule and have about 7 hours on the engine. Schedule requires 25:1 for the first 10 hours then 100:1.

Engine runs on 1 cylinder at low speed but #2 kicks in with some throttle and then is pretty reliable as it heats up.

I had an older (2006) non-enduro Yamaha onnthis exact same boat (12í Porte boat) last year and it ran great. It would push my wife and I up on plane at 3/4 throttle and hold us ther st 1/2 throttle. This one will get me alone on plane (barely) but will not plane with both of us. BIG DIFFERENCE. This engine is a DOG.

Came with a 7x9 prop, I changed to a 8-1/4x8 prop, no big difference.
I changed plugs. No big difference.
Yesterday I cleaned the carb. No sign of varnish, no difference.

No taking it back to where I bought it, many miles ago. Tried to get it to a Yamaha mechanic here in Georgetown, Bahamas, but heís been sick for a week. Now we are leaving to head South. It works, but poorly.

Can it be the 25:1 oil mix ratio? Will this clear up when I go to 100:1?

Any other thoughts?
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Old 22-01-2018, 07:52   #2
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Re: New 8hp Yamaha enduro runs poor

I don't see anyone using 100:1 in Central America, everybody uses 50:1 in an Enduro. You should switch from the 25:1 mix or go to a warmer spark plug.
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Old 22-01-2018, 09:12   #3
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Re: New 8hp Yamaha enduro runs poor

A few facts to consider

The Enduro is 20 pounds lighter than the 4 stroke so the weight distribution in your boat will be more bow-heavy, which may be part of the problem.

Oil:Fuel mixture is unlikely to have anything to do with the problem.

You may still have the wrong prop for your situation.

Have you adjusted the mixture settings on the carb? They typically can't be set properly except under load, and they do affect performance.
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Old 22-01-2018, 09:17   #4
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Re: New 8hp Yamaha enduro runs poor

Both engines were 2-stroke, same weight.

I only found 2 props available online and this one is nearly identical to the one on the old motor.

No I haven’t adjusted mid settings. I’ll have to dig into that.

Yeah, I can’t imagine the oil mix will matter that much BUT something is different.

I have fooled around with the tilt and got that where it feels right. About the same as before.

8hp is a lot of motor for this boat. 70-80lb boat weight.
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Old 22-01-2018, 09:43   #5
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Re: New 8hp Yamaha enduro runs poor

I have the exact same problem with my 15hp two-stroke Yamaha whenever I take it out of extended storage. Clean the carb again, and focus on the jets - they need to be removed and soaked in carb cleaner, and carefully inspected.
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Old 22-01-2018, 10:30   #6
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Re: New 8hp Yamaha enduro runs poor

We have an 8hp Enduro and it took me 2 tries to get the carb clean and run right. I never did see anything wrong or dirty.
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Old 22-01-2018, 15:06   #7
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Re: New 8hp Yamaha enduro runs poor

Iíve had similar troubles with my Enduro 25 that was new a year ago also though it hasnít been in storage. This Fall and Winter, weíve fouled plugs every few weeks (tips black and generally dry). It doesnít feel like it has full power. Changing the plugs restores the performance mostly, but only for a couple of weeks.

We had not been able to locate a new carburetor until today and still havenít been able to get a seals kit to rebuild the original one. Iíve had suggestions that:
1. the fuel/air mixture is wrong (I.e. the air mixture screw on the carb needs to be adjusted, but changing it doesnít seem to make a difference),
2. the oil-gas mixture needs to be adjusted (weíve strictly followed the manual-suggested 100:1 ratio),
3. there might be water in the fuel (have changed tanks and run a large water separator in any case), and
4. we need different plugs (different from those recommended in the manual), etc.

I put the new carburetor on today and perhaps that will solve the issues, but would appreciate any ideas you all might have. The old carb looked clean and the jets I looked at were clear. Understood that they might still need to be cleaned per the earlier post.
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Old 22-01-2018, 17:58   #8
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Re: New 8hp Yamaha enduro runs poor

Quote:
Originally Posted by J120Heron View Post
I put the new carburetor on today and perhaps that will solve the issues, but would appreciate any ideas you all might have. The old carb looked clean and the jets I looked at were clear. Understood that they might still need to be cleaned per the earlier post.
A possibility to consider with that particular history is that the float may be stuck open, or partially open, usually due to debris in the little valve seat. Bane of many carbureted small engines, especially those that see seasonal use. If so the new carb should clear it up.
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Old 22-01-2018, 19:06   #9
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Re: New 8hp Yamaha enduro runs poor

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Originally Posted by hpeer View Post
Bought a BRAND NEW 8hp Yamaha Enduro last spring. The shop ran it and gave it to me. I stored it on the boat for 8 months before running it.
.......
Did you run out the fuel in the carb bowl before you stored for 8 months? Are you running now on fresh fuel? It sounds like the low speed jet is not clean. These things are small and take some finesse to clean.
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Old 23-01-2018, 02:01   #10
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Re: New 8hp Yamaha enduro runs poor

Yamaha recommend to run at 100:1 when using ONLY Yamaha oil and 50:1 for anything else.

Seems a little risky but I did it for 10 years on a Yammy 25 hp and it ran fine.

Feel free to run at 100:1 but be careful and err on the side of caution to add a little more to be safe.
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Old 23-01-2018, 02:37   #11
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Re: New 8hp Yamaha enduro runs poor

What colour are the plugs when you remove them after a run?

Still running in will not give 100% power.
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Old 23-01-2018, 12:33   #12
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Re: New 8hp Yamaha enduro runs poor

I am surprised to hear you say the enduro will after breakin, run on 100/1.
My Enduro 8 ran on 50/1 after break in. I was poorly advised by a mechanic in Ecuadore to run it at 80/1 as it was being used on my dingy as opposed to being used commercially pushing much more weight than my dingy. Ended up burning up the engine. So what ever the outcome of your present problem which should be under warrenty. You should double check that mix ratio. My previous Yamaha 2 stroke 8 hp outboard purchaced in Seattle many years ago had a break in ratio of 50/1 then after break in 100/1.
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Old 23-01-2018, 12:50   #13
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Re: New 8hp Yamaha enduro runs poor

What oil brand did you use? It MUST be run on the correct Yamaha oil if run at 100:1 and the manual said 50:1 for other brands of oil.
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Old 23-01-2018, 18:03   #14
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Re: New 8hp Yamaha enduro runs poor

2-stroke mix oils are not all the same thing in a different can... The oil that works great at 50:1 will seize you up at 100:1. And the oil that is designed for 100:1 will gum you up at 50:1. Likely you have fouled the #2 plug which only starts firing after the engine is warm and the crud on the plug melts off. Also, if the fuel in your engine is 8 months old, toss it and refresh with a high octane. Use a can of aerosol "Sea Foam" to clean the the intake while the engine is running. Your plug tips should be a matte dark chocolate color - even in a rice burner. If they are black (shiny or matte) you have bad gas and/or too much premix oil. DO NOT go with a hotter plug - you can melt a hole in the head of the piston and DO NOT change the pre-sets on the carb as you can seize up the motor or cause too much "step" from idle to low speed to high speed - three different jets that must work in tandem.
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Old 24-01-2018, 01:05   #15
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Re: New 8hp Yamaha enduro runs poor

The reed valves behind the carby are probably gummed up. It can happen if engines are stored for a long time. Clean with brake cleaning fluid--give them a good wipe down=--and replace. Mine worked well afterwards--but it was not a twin--just a 3.5 single popper.

Dump the old fuel and flush the tank with clean fuel and discard that too. Then fill with clean NEW fuel mx. Stating the obvious I know--


As to your oil mix ratio--yes--it will run better on 100:1. Once you have reed valves that work. If it is not completely run in yet, perhap try 50:1 for a while then go to 100:1. I keep mine at 50:1. They may last a bit longer.
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