Still figuring out this old two stroke outboard....

K

Kris Winiarski

Member
This past fall I sold the really nice 20hp honda I had on my boat and replaced it with an early 90s 30hp yamaha two stroke that I picked up for cheap. After a few hours disassembling the carbs and cleaning out all the jets, adjusting the mixture screws and idle screw (with help from Jode), I had it starting after a few pulls and running really nicely. That first trip after cleaning the carbs I was pretty amazed how much more speed and power the motor has to get up on plane with some weight in the boat versus the honda, given it only weighs another 20lbs or so.

Fast forward to duck season it was still running well but I found it was a bit harder to start that first time on colder mornings. After a little bit of tinkering I found that it started much easier in the cold if I maxed out that idle screw. After that adjustment it started easily and ran great a handful of trips this winter, but the last weekend of duck season, I found that it wouldnt idle in neutral without the choke out and would bog down when giving it gas. I'm assuming when I pop the carbs off again that I'm gonna find a clogged jet.

I'm curious to know if folks think that it clogged up again because I was running with the idle screw maxed out or if that is completely unrelated? Do these older two strokes, even when routinely run, just get some junk in the carbs from time to time... or should I be able to go a few years between carb disassembly when I run it routinely? Would a small water separator help or is that unnecessary here? Should I start buying gas without ethanol from the docks?
 
Don't forget your fuel hose. Really cold temps adversely affect the hose to fitting connections. I have less than pleasant memories cutting two hose assemblies up and swapping fittings and hose clamps - 4:30 am dark and in temps right around zero F. Got it to work but wasn't pleasant. Your performance description is similar to what I was fighting with the last summer which turned out to be hose related.

Good luck!
Scott
 
You shouldn't have to have the idle screw all the way out to get it to start, even when cold.
And in that position, it should idle, without the choke out.
Throw in bogging down, add it all up and sounds like a fuel supply problem.
I'm agree on replacing your supply lines & blub and making sure your connections are solid.
And check your gas supply, make sure you dont have water in the tank.

if its any consolation, I'm chasing similar problems with my Merc 25, I haven't worked on it in a while but am looking to rebuild the fuel pump this spring.
 
All of these comments are spot on. Also be sure to add Stabil or something similar to your gas. The carbs do not like ethanol fuel and its really easy to gunk them up. My suggestions follow all the advice here, I would add to check the fuel pump. Also ensure that you fuel vent in the gas cap is not iced over or clogged, this will cause a motor to die out rather quickly, i've experienced this before.
 
Basically, a visual inspection of the entire fuel supply line including the fuel pump housing is worth it in an engine this old. Try to see if you can get a supply of non-ethanol premium to do a comparison with another fuel line suppling gas. As several others have mentioned, plastics in this era were not chosen for their resistance to water absorption from your fuel supply, which causes the polymer to swell and alter fuel delivery rate. Using something like Stabil pulls water into solution. The big question is does this aid adsorption into the plastic polymer array or lower it
 
agree with all of the above and throw in the fuel filter and or fuel/water separator. They may be blocked even with small particles of ice in your gas.
 
Kris, how much fuel do you use in a season? Twenty or 30 or even 40 gallons? The difference in cost between ethanol (E90 I hope --not E85!) and non-ethanol per season might be insignificant compared to the troubles you may potentially be introducing by using ethanol fuel. If you add a fuel filter/water separator but continue to use ethanol fuel I doubt that you will see much improvement because any water that may be in your ethanol-filled tank is going to be totally mixed-in with the ethanol fuel. Take a sample from your fuel tank and examine it in a clear glass jar for cloudiness which would indicate water is present. On the other hand when water is present in a tank of non-ethanol fuel the water separator will be able to do its job. (If you test a fuel tank of non-ethanol fuel for water the sample must be taken from the bottom of the tank--using a glass turkey baster or similar--keep in mind that water is much denser than "rock oil" gasoline 8lbs/gallon vs 5 lbs/gallon). I am unsure what happens in freezing temperature re: ice crystals forming in a tank of ethanol fuel vs. non-ethanol fuel. Not to sound like a broken record but unless it is extremely inconvenient for you to buy non-ethanol fuel then I would spring for the difference in annual cost. Keep in mind that non-ethanol fuel has more energy per volume so this offsets the higher cost a little bit. Although I am a big fan of non-ethanol in smaller outboards I ran ethanol much of the time in my 90hp Johnson and added Stabil. But I don't believe that adding more chemicals (Stabil) to ethanol fuel thereby creating a Witches Brew of who-knows-what is better than non-ethanol fuel. I have been told that Stabil has enzymes that eat the water and convert it to combustibles....hmmmm.
I've owned/worked on only 1 small Yamaha outboard so I don't know much about Yamahas compared to what I have learned on Johnson/Evinrudes. On some Johnson/Evinrude models it has been found that: 1)positioning the Spark Plug in a particular orientation provides better starting 2) in extremely cold weather at the ramp removing the spark plug, heating with a propane torch and reinstalling the spark plugs can be a fix. Other members have provided a lot of good ideas but if none of these work then you might put your questions up on iboats.net Forum under the Yamaha section.
One more point..although I too use Starting Fluid on occasion for 2-cycle engines some of the most respected experts advise against this as it may be harmful if/as the Starting Fluid has no oil lubricant. Instead they advise squirting fuel/oil normal mixture into the spark plug holes to prevent wear and loss of Compression.
Best of luck figuring this out...start with known-good fuel...
 
OK... thanks for the comments. I've been running regular gas from the gas station, but I'll try to just buy non ethanol from the docks here and see if it makes a difference. The boat is in the water year round down here in Maryland and gets used consistently so I assumed I didnt need any additives with quick turnover of the gas (I also frequently just dump whats left in the tank into our minivan when I fill the 6 gallon tank). [/url]

I'm gonna take the carbs apart this weekend, clean out those jets again and see if that gets it running well like it was previously.
 
Kris,
I have the same motor down here in NC. I learned the hard way to only run non ethanol gas.

I have not had any issues with starting no matter the weather or the temperature.

Larry
 
Kris, lol you might be "lubing up" the rings/cylinders in your mini-van with that residual 2 cycle fuel--depending on volume you are transferring. But probably no different than some newer vehicles which are actually designed to consume oil. We had a Recall on our 2016 van but only if the engine was burning more than 1 quart every 4500 miles or something like that. Weird...
 
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