chances rich 2-stroke mix hangs up carb?

[1 FMF]

have new yamaha 25hp 2-stroke outboard, still less than 10 hours on it so been running premix at 25:1 with yamaha oil. Have about 5-6 hours on it currently. Been running great for first 3-4 hours, lots of power and hits top rpm. Tach reads 5800 rpm.
One time cruising around 4000 rpm had to avoid some junk in water so I rapidly closed the throttle. Ended up stalling motor, was very hard to restart, when running sounded funny at idle and wanted to stall unless I gave it throttle and ran > 3000 rpm. So i ran that way back to the dock for about 10 minnutes. Got back to dock and motor all better.
Ran fine for next week.
This past week been losing top rpm, dropped to 5200 wot at first now it won't get on plane and loses all power anything greater than 2000 rpm. If i pull the choke it roars briefly and I can feather the choke for about 2 seconds at most to get power.
Brand new gas tank and it's fresh gas. So i'm hoping it's a gummed up carb from all the oil, a stuck float maybe.
I've pulled the plugs and they look great, they are clean no deposits even. And the motor will idle and run < 2000 rpm fine, with expected amount of smoke.
Anybody with similar experience?

 

[mikeg5]

welcome to the world of fickle 2 strokes.. ill be glad when everything goes to 4 strokes.. yeah they are a little iffy right now but that will change..... take your carb apart and inspect and clean. check the choke too

 

[Pablo]

Most all 2 strokes, at the very least, need the jets adjusted during breaking/set in.

I doubt the float is stuck (it has a float?), but you are on to something......I can't testify to the Yamaha oil, but after you verify the cleanliness, get a good oil, select a good ratio and then adjust your jets.

 

[Steve S]

Talk to the dealer the problem sounds more like some kind of lean condition because of what you said about pulling the choke and it seems to run better .I don't think oil gums up a carb unless it sits for a long time and the gas evaporates. In the early 80s my friend let me store and use his 14 foot with a 35 Johnson for 4 years when he went to med school the thing was 100% reliable so hopefully the problem is simple like some crud in the carb.

 

[1 FMF]

Already have the carbs off, really nice setup. Has nitrile o-rings mounted into the carb base plate, so I can remove them with never a need to replace gaskets to the intake. It's so nice i'm almost happy to wrench on the thing.
Took me about 5 minutes and that's with the learning curve of finding what nut/screw holds what on. Will get around to pulling the bowls off the carb this evening. Had talked to the dealer and it sounds like a common problem. I'm good with carbs so all he said i needed to do is just pull the bowls and clean out the main jetting.

Not sure if there are floats or not. My 9.9 merc has a float, and most carbs on similar sized motors (even lawnmowers although 4-stroke) have floats. But I may not have floats now i think about it remembering how small the bowls seemed to look. would be awesome if no float, just one less thing to go maintain.

pablo, what do you mean most all 2-strokes need jets adjusted?

i've been running yamaha oil at 25:1 to 20:1 premix ratio since 1st startup. Now have about 6 hours on engine. Smokes quite a bit at idle but pretty clean when running 3000+ rpm. When I pulled the plugs they looked brand new except for a thin amount of black on the end of the threads. The porcelain and ground strap electrode were completely clean! Never seen a 2stroke spark plug that clean before, and this was after the motor missing and not getting past 2000 rpm.

 

[1 FMF]

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welcome to the world of fickle 2 strokes.. ill be glad when everything goes to 4 strokes.. yeah they are a little iffy right now but that will change..... take your carb apart and inspect and clean. check the choke too

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dude your crazy. the only! good thing about a 4-stroke outboard is the cost savings of not burning oil.
an equivalent 4-s will never match the power and performance of a 2-s, and everybody will be even more screwed in the future as fuel quality/performance/economy degrades with more ethanol and gov't interference.

i did a bit of research before buying my 25. Was going brand new and spending $2k so i wanted the best for my money. check out the weight differences, also note the extra cylinder needed for the 4-s. The 4-s defeats the whole purpose of an outboard and its exaggerated by their inability to produce low rpm torque. Friend bought a 15hp 4-stroke merc and was disappointed in it's low rpm power and wishes he went 2 stroke. It gives him good top speed on his 10-12' raft but a 10hp 2-stroke he had gave him equivalent or better out of the hole jump. I could be ok with less power of a 4-s outboard vs a 2-s, that's very understandable if not expected, but the weight issue is inexcusable. The emissions claim is a joke because 2-strokes can run very clean if maintained, and 4-s can run dirtier because they are not immune, they have carbs and can run rich, and also burn oil. On paper it may look better but real world is a different story. just read some of the boating forums, plenty of posts about help me with my 4-stroke outboard.

Merc 4-s 9.9hp 2-cyl 209cc 55x44mm 84 lbs
Merc 4-s 15hp 2-cyl 323cc 59x59mm 111 lbs
Merc 4-s 25hp efi 3-cyl 526cc 61x60 157 lbs
Merc 4-s 30hp efi 3-cyl 526cc 61x60 172 lbs

yam 2-s 9.9 2-cyl 246cc 56x50 79 lbs
yam 2-s 15 2-cyl 246cc 56x50 79 lbs
yam 2-s 25 2-cyl 395cc 67x56 106 lbs

Anybody know what merc does to make a 5 extra hp from 25 to 30 and what introduces 15 lbs?

 

[cruisertech]

How do you adjust A jet?

 

[Pablo]

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pablo, what do you mean most all 2-strokes need jets adjusted?

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I have found with some 2 strokes as they break in the idle jet in particular needs fine tuning. Maybe the factory setting isn't ideal for the particular conditions or mixture. I'm not sure of your engine set up, nor especially what kind of main jet you have. I have no idea if this is your issue at this point.....but what have you found out? Did cleaning help?

 

[Pablo]

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How do you adjust A jet?

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It depends - most engine manuals supply the basics. Some of the power mechs here can probably help with your engine.

Here's some old fashioned stuff from the web:

Basics 1

Basics 2

 

[1 FMF]

Don't remember seeing the idle/pilot jet but the main jets are 1.25mm. Checked the 40-70hp models and they run a 130 jet, but I don't know if it'll fit in my carb. Might have to sacrifice $15 to find out. Otherwise nothing else is available, I've called extensively to find larger main jets.
The pilot circuit side of things I think is fine, don't see any need to mess with that yet. Mid throttle runs fine. have a problem right now with idle, i sheared off the mixture screw on one carb cleaning it (see mechanical forum) so I think it's screwing itself inward and the motor sneezes a lot at low idle.

On the lower carb I had some junk stuck in the main jet. Also had a lot of black flecks in my fuel filter on the engine, might be coming from the inside of the fuel line, will have to keep an eye on it, although the 6-gal tank it was on was old and shot from sunlight. also had a crack in it so may have gotten a little water in the fuel.
cleaned everything out, thing runs f'ing awesome. GPS'd and laser rangerfinder averages me at 39 mph, 42 at one point going with the tide.

running a turbo stainless prop, 10x14, turning 6000 rpm wot.
gonna see if i can't get a 10x15 or get my 14 double cupped. Hoping to get a solid 40mph out of it wot.

Still running 25:1 to maybe 40:1 premix. have about 6-7 hours on it. Should I expect more power after 10-20 hours when I start running leaner oil mix? I'm supposed to run it at 100:1 but I think I will stick with 50:1 and keep an eye on the plugs. At 25:1 they're amazing clean.

 

[Master ACiD]

dude 25:1 is a bit rich for a end user outboard. that engine was probably fully broke in 30 minutes after you first started it.
in a 2 stroke, the only things that really break in are the piston, rings and cylinder. the crank and rod bearings are ball or needle, and those type of bearings dont really break in.
jump to 50:1 or 40:1 and dont look back.
with that said, the oil isnt youre problem.
black flecks sound like fuel line problems. also i dont think youre main jet is the problem (unless its clogged) because you said the thing pulled 5800 rpm on the original jets.
id clean out the fuel line and carb and install the filter right before the carb, so as to minimise the length of line between the filter and the carb. then grab a pair of new plugs just for testing purposes. if the plugs dont fix anything throw them in youre toolbox and keep them as spares. you should have spares on hand at all times anyways so buying plugs are justified.

pull 1 plug and take a look at the spark too. a coil going south can have enough energy to spark a plug at low and mid rpm's but not enough to do it at high rpm's.
i had this happen to a honda dirt bike i just got done overhauling. i ended up putting a petronix flame thrower automotive coil on it, but thats another story. hehe

 

[1 FMF]

update: all the problems i'm 100% sure were caused by an old fuel line i was using from my 6gal tank to the motor. The interior of it had to be flaking away,,, ethanol (alcohol) in the gas maybe causing it?
i replaced that with the new one that came with the motor, should have done that before putting the motor on the raft,
haven't had a problem since that change.

even when i ran the mix at 25:1 with yamalube, the plugs looked like they came out of a 4-stroke they were so clean.
after the 10 hours, i slowly leaned it up to 40:1 then to 50:1, then the leanest at 80:1. after the 80:1 tank of gas, i've been running around 50:1 to 70:1 ratio,

the original prop that came with the motor spun up to 6800 rpm, i finally figured out the pole setting on the tach. I've since gotten a nice 14" pitch stainless turbo prop on it and can almost do 39 mph consistent wide open at around 5800-6000 rpm. I usually run it around 4000-5000 rpm, but often have too much fun w.o.t. Got the motor home now for the winter, plugs are clean as can be. The whole problem was junk clogging up the main jets, the one time i pulled the carbs when the raft wouldn't get on plane i could see a clog in the main jets. I have pulled the carbs a total of 3 or 4 times, but after the fuel line change i pulled the carbs once, blew them out, and have been faster than most big boats since

 

[Pablo]

Quote:
The whole problem was junk clogging up the main jets, the one time i pulled the carbs when the raft wouldn't get on plane i could see a clog in the main jets.


Wow - thanks for checking back and following up!

 

[Gillsy]

Not all four strokes are created equal. My last outboard was a re-badged Suzuki DF-140. It was a 16 valve dohc fuelie that kicked butt, and was the most satisfying marine power plant I ever owned, and I owned six boated. This thing would get 6-6.5 mpg, and push my Larson SEI 180 to 48 mph gps with five people on the boat. Very quiet. I understand that the Yamaha F-150 was very good also. Neither of these engines offered the brute force of a two stroke, but they are very good engines.