New 8hp Yamaha enduro runs poor

[hpeer]

A64,
Your edit somewhat matches missing sysmptoms except it still has low power at high rpm. I think it runs rough at high rpm but that is very subjective. The low power is not subjective, same exact boat had a different 8hp Yamaha 2 stroke last year and ran great.

I bought the engine in Bahamas last year and it sat for 8 months before using it. I’m in DR now and won’t find a dealer before PR. And they may not want to work on 2 stroke, don’t know.

I ordered the power pack and will swap that out as relatively cheap trouble shooting.

[a64pilot]

With the enriching circuit on, even full throttle will be rich, not as rich as idle and low RPM of course, but it will be Rich,
Several years ago I bought a little boat for cave diving, it has an old Mariner 25 Hp on it, and old Mariners were Yamaha’s.
Anyway ran like crap, I thought maybe it was the carb so I too, it apart and cleaned everything to no avail, then got parts breakdown of the carb, turned out it was missing the little BB and spring from the enriching circuit, so it was on all the time, replaced those and it ran like a dream.
I’m not saying of course yours is missing parts, but if you can get ahold of a carb, it might be worth a try.
A spare carb with today’s fuel is not a bad thing to have.

[sandiegoskipper]

Is there any spark timing adjustment or some spark advance mechanism? I'm just wondering if the timing could be off slightly on the one cylinder...

[Mike Banks]

If it has the right mix o9f gas, proper spark and the reed valves and pluf-ga are OK and the leads have been replaced--then it has to be either a crankcase leak (id=f a 2-stroke) or the timing is out.

Start with the most obvoius first and work your way through.

In the spark department I had an engine that I had done everything to and it started well but had no power at all. Eventually, I replaced the capacitor in the ignition, just as a gesture of hopelessness since it was fine when tested at the auto electrician's shop.

That was all it was-OK cold but faulty at revs and when warm. It may well be your ignition system.

[paulajayne]

Originally Posted by hpeer

They are black but not terrible. No deposits or build up.
.

It is running rich. Either too much fuel or not enough air. Ensure choke is off (Cold Start).

Try running without air filter to test - not for too long.

Remove and recheck plug colour.

http://www.apriliaforum.com/forums/a...7&d=1341312352

[hpeer]

Weeelll.... from that chart I would say they look “oil foiled.” Black, no carbon. When I take the plugs out there is oil on the plug threads. The gaps are dry but black. I replaced the plugs once, I’ve cleaned the plugs one, lightly touched them with some 800 grit. There was no build up on them so no need to be harsh with them.

This is a 8hp so I don’t think the carb is quite as complex as a 15 or larger. I did watch another guy clean up a 15 Yamaha carb and he had 2 jets in the carb that he unscrewed. I didn’t see the whole thing, he just gave me a summary, 3 minute tour.

The one jet that does unscrew is a machined brass tube. There are some tiny holes in the side of the tube. I had expected to see something inside the tube but no, it was just a smooth tube with a machined lip on the upper end, in the Venturi. I was damn careful not to loose anything whit dissassembly and looked around for anything missing but no, just a smooth tube - maybe 3/16” diameter.

I will look at choke linkage. The choke “works” as it’s supposed to. There is no “air filter” as in some kind of medium for the air to pass through. There is a plastic chamber the air goes through, but it is just passages. Unless I missed something but I don’t think so.

[jimbunyard]

Originally Posted by hpeer

Just an update, not a lot to add.

The engine is now past the break-in period, I’m running it on 50-1 mix as prescribed.

It is very marginally better. I have cleaned up the plugs, they both look about the same. They are black but not terrible. No deposits or build up.

The engine still misses at low speed then the second cylinder cuts in. To my ear it still feels a bit rough. It starts easily.

Although slightly better it is still VERY weak compared to the old 8hp motor I took off.

I’m suspecting the power pack. Hard to imagine what else could be wrong.

If this is the manual for your engine

http://www.yamaha-motor.com/assets/s...06-91_1392.pdf

the correct ratio is 100:1 after break-in. Kiss philosophy would say empty the gas tank, put in correct ratio fuel, 'clean' the business end of the plugs with a propane torch (not too much!), and give it a try. If that doesn't work, put new plugs in and try again. If that doesn't work, go up two heat ranges on plugs and try again. Then try your new coil.

If you're uncomfortable running at the factory recommendation, but the engine runs well there, bump up the oil ratio until the performance becomes unacceptable, and dial it back a little from there...

[belizesailor]

Does that manual cover the Enduro series (too slow to download here)?

Ive not encountered an Enduro that runs 100:1, but that dont mean it doesnt exist. [emoji6]

[jimbunyard]

Turns out it's for an 8MH, while an Enduro 8 is model 8CV I think, listed at 2% mixture, so it's back to the drawing board...

If everything else is kosher, as it seems to be, and the engine was running well when it was laid up, I wonder if something could have crawled up inside some water or exhaust passage and clogged things up enough to cause a problem...

[hpeer]

I bought in April of 2017. The shop (Abacos, Bahamas) obviously it for a bit before giving it to me, I’m guessing just 5-10 minutes to make sure it worked.

I then immediately put it in storage and only took it out in December. It was buried deep underneath our bunk.

So it has always run like this. Always missed. Always low power.

My first thought was “Can there be this much difference between a Enduro (50:1) and a “regular (100:1) 2 stroke?”

I’m in Luperon now, will be in PR in a few weeks, then on to the VI’s and down island chain to (hopefully) Grenada by late May. No taking it back to dealer on warranty stuff. I’m on my own. I tried to have a dealer look at it in Georgetown the the mechanic was sick while I was there and had a huge backlog.

[jimbunyard]

The nature of these somewhat subjective problems often makes them very difficult to resolve.

That the engine starts easily and (apparently) runs throughout it's operating range makes the electrical system a less likely root source, though a 'weak' coil or corrosion in a connection somewhere could conceivably cause the symptoms you describe.

Not knowing the history of the engine (was it new from the dealer, or did they get it from another source; did they repair or change something, possibly mixing something from a different model with the Enduro model? Like a carburator?), as a diagnostic you could run the engine on a 100:1 ratio long enough to see if the problem goes away, without causing any ill effects in the time needed to verify the power output.

If it does you've at least eliminated some of the candidates and can concentrate on the fuel system, which from your description sounds like is the problem anyway.

Since the engine appears to be loading up; running too rich, I'd concentrate my efforts on narrowing down the causes of that. Intuitively this would seem to preclude a 'clogged' passage or jet, but small engine carbs are very intricate and if a vent is blocked it could result in a rich running condition. As could an improperly set float level.

If testing with a 100:1 mixture, I'd definitely use new plugs, or at least 'clean' them with the torch method described previously, as plugs run in a consistently rich environment can fail to provide a good spark when under compression...even if the spark looks 'good' out in the open.

[hpeer]

Jim,
It was purchased brand new from a Yamaha dealer in the Abacos.

[a64pilot]

Just me, but I’d never run anything on 100 to 1, even if it was supposed to.
Little motors that I run hard, I run on 25 to 1 and bigger watercooled motors 50 to 1,but 100 to 1 is nuts I think.

By the way, I don’t foul plugs at 25 to 1 either, and certainly not at 50 to 1.

Get a carb, I think so many people change carbs now days that these things are so hard to clean, that they are stocked.

[hpeer]

First....
Seems to have been the carb. I got a new carb, it’s running better, not as good as the old engine but deffinetly better. Smooth through the rpm range.

Second....
I’ve bee travelling the thorny path
DR: only Yamaha dealer was in Santo Domingo, too far away
PR: only Yamaha dealer would not service the engine. apparently they do not service Yamaha engines but immediately told me to call some guy
BVI: Yamaha dealer is Tradewinds at Nanny Cay.

At Nanny Cay they refused to work on the engine. The Manager accused me of “tampering” with the engine because I had adjusted the lean screw and changed the prop. He kept miss-interpreting my words in an accusatory manner. He challenged me on the oil fuel mix required. Unbelievably he apparently didn’t know how to calculate the mix himself. By his own words all he knew was 3 gallons required a “bottle” of oil. When I asked if that was 16oz or 32oz I got a look that said he didn’t know and no verbal answer. Simply put he was arrogant, ignorant, and insulting.

I was able to buy a carb and installed it myself. Apparently even that is not allowed, I overheard another gentleman being told he was allowed to do NO work on his boat. “Maybe if you do a little painting inside that would be OK.”

I know some folks have a great experience at Nanny Cay. Others have also had a bad experience. This was mine.