yamaha 25 two stroke running on 1cyl

[Av8erdunn]

I have a 99 yamaha 25 that has started running on 1 cyl. It started with me forgetting to vent the fuel tank. We were running from a storm and I barely made it back to the marina About the time the bulb collapsed and it started running like crap. Now it's only running on one cyl. The oil was low as I just got this engine and was debating disconnecting the oil injection and was running pre mix. It's almost like its running in a safe mode for low oil but the light didn't come on nor is it ever on while running. It's run great for the last 6 hours I have used it up until now. I run a compression check and she is sitting at about 116psi on the dead cyl and about 112psi on the working cyl. I have taken off the carb and checked it and it was perfectly clean. Reeds looked good from looking through the intake and I replaced spark plugs hoping I had a bad plug. I even went as far as swapping the coils to see if the dead cyl woul follow but it didn't. The odd thing is if I put the motor on the hose and rev it up in gear it will run on 1 cyl until it gets higher up in the rpm range then you can hear the second cyl kick in. It's got me puzzled for sure. Any ideas?

Also how do wire up the wires on the oil tank level so they will not throw an alarm without he oil tank being on the motor? It's just a ping and black wire as shown in the pic.

[Av8erdunn]

Here's the pic. Sorry I forgot to add it

[99yam40]

I have a 99 yamaha 25 that has started running on 1 cyl. It started with me forgetting to vent the fuel tank. We were running from a storm and I barely made it back to the marina About the time the bulb collapsed and it started running like crap. Now it's only running on one cyl. The oil was low as I just got this engine and was debating disconnecting the oil injection and was running pre mix. It's almost like its running in a safe mode for low oil but the light didn't come on nor is it ever on while running. It's run great for the last 6 hours I have used it up until now. I run a compression check and she is sitting at about 116psi on the dead cyl and about 112psi on the working cyl. I have taken off the carb and checked it and it was perfectly clean. Reeds looked good from looking through the intake and I replaced spark plugs hoping I had a bad plug. I even went as far as swapping the coils to see if the dead cyl woul follow but it didn't. The odd thing is if I put the motor on the hose and rev it up in gear it will run on 1 cyl until it gets higher up in the rpm range then you can hear the second cyl kick in. It's got me puzzled for sure. Any ideas?

Also how do wire up the wires on the oil tank level so they will not throw an alarm without he oil tank being on the motor? It's just a ping and black wire as shown in the pic.

that don't look like a ping wire to me

[Av8erdunn]

This for pointing that out. It's PINK.

[99yam40]

what does this mean?

So did my response on the other forum give you something to look at?
Or are you just looking for more answers before you have a look?

[Av8erdunn]

I am wondering what to do with those wires since I have taken off the oil injection.

[99yam40]

did you not understand what I wrote on the other forum?


Yamaha oil injection is gear driven from crank shaft, if it turns it will pump.
keep it all clean and test as Yamaha recommends and it will sure you well for many years

[Av8erdunn]

Actually I didn't even get a notification that anyone had responded to my post. Sorry!!! I guess that's a possibility but why would it work for one cyl and not the other?

Thanks for the replies both places.

[99yam40]

why do you think it is not working properly?

hard to figure out what problems you are having if you do not post the info

[Av8erdunn]

I'm talking about your response to the fuel pump when you told me to check it. Why would it work for one carb / cyl and not the other? I will put the oil system back on once I get her running right.

[99yam40]

float.needle and seat, and line should be the only things that would keep fuel out of carbs.
But passages in carbs would be the things that normally plug up on individual carbs

Oh yea there are check valves and lines that need to be checked along with crud/water in the tank that has to be addressed as far as keeping it clean

[Av8erdunn]

I cleaned the carbs and they were clean as a whistle and I ensured all jets were free and clear. When I took the carb apart the carb for the dead cyl1 was full of fuel. So I have compression, fuel and spark and she runs like crap. That's why I was wondering if it could enter in a safe mode or something when low on oil in the tank? It almost like timing is retarded on this one cyl. The fuel tank is clean; I just bought it and cleaned it good prior to putting any fuel in it. I checked for water and that's a negative.

[99yam40]

timing light will show if timing on a cylinder is off, but I do not see how that would happen

compression, spark, timing, and proper fuel to air ratio is all that is needed

[Av8erdunn]

That's why I'm so puzzled. I have everything I should need to run and she's a no go. I'm gonna check my fuel pump tomorrow after work and I will report back on what I find. I'm keeping my fingers crossed but since I had fuel in the bowl I'm not too optimistic. Thanks for your help.

[Av8erdunn]

Well I think I figured it out, my idle air screw on top of the carb had come out. Undoubtedly the previous owner had messed with the screw and didn't put the spring back on and it backed out. I have to put the carbs back together again and reinstall the needle valve when I buy a spring and give her a try. If that fixes it I'm gonna reinstall the oil injection and give that a try as well.

Thanks for all the help.