Dead Cylinder

[sonat]

I have a '92 115 that has not been run for about a year and a half. before starting it I replaced the plugs and added new good fuel. when I fired it up it has one dead Cyl. it has fire to all plugs and I changed the plug on that cyl again and still is dead. the compression is 110 lb on all cyl's except the daed hole and it has 100 lb. when I pull the plugs out all plugs show a little oil and gas on them except the dead hole and it looks dry. I'm thinking I have a stuck reed valve on that cyl. does is sound right? is there anything I can spray into the carbs while running to free up a stuck reed valve? or is removal the only way? thanks for your input.

[jb123]

a stuck reed would have blowback thru the carb.
id suggest a good carb cleaning and and for the compression, a shock treatment of ringfree or seafoam , hopefully the ring may be stuck and hasnt slapped in the cylinder too long.

[Ken]

Hey, jb, with a stuck (closed) reed valve, would you still get blowback thru the carb ?
I could see it if it were stuck open - dunno.

sonat - you could have a stuck (closed) float valve in that one carb and not allowing any fuel into the bowl. I would do as jb suggested and try a shock treatment with RingFree or SeaFoam.
Here's my procedure with SeaFoam that I use on my C115 - this is from a previous post:

Two strokes build up a lot of carbon internally and need to be de-carbonized by doing a "shock treatment" with a detergent like Seafoam.
I like to do the shock treatment once a year on my C115 - in late winter when I am going thru my list of "spring make-ready".
If you use a detergent like Yamaha Ring Free or SeaFoam all the time in your fuel tank, then the carbon buildup is not as bad. Still, a lot of 2-stroke owners will de-carbonize once a year - you will get various opinions on this.
I "shock-treat" my C115 by running the following mixture thru it. This will smoke up the area pretty good, and leave a lot of carbon on the drive way:
16 oz can Seafoam
3/4 gal gas
3 oz oil (2 if oil injected)
Disconnect the fuel line at the input to the bulb and attach a three foot piece of fuel line to the bulb. Mix the above in a small container -
I use an empty 5 quart oil jug. Set the container on the deck of your boat and insert the fuel line and secure to make sure the end stays on the bottom of the container. Pump up bulb and start outboard with earmuffs and water hose, of course -run a little above idle for 15 minutes and turn off. Let sit for 15 minutes. Run again for 15 minutes. Let sit 15 minutes. Repeat until all mixture is consumed. Reattach main tank hose to bulb and run regular fuel/mixture thru motor for 10 minutes - you want to get the concentrated detergent out of the fuel system.
Now, clean up the drive way before your wife sees all that nasty carbon and makes you get rid of your boat.

If the shock treatment doesn't work, then you're gonna have to tear down those carbs, clean, and install a carb kit.

Good luck [img]smile.gif[/img] ,
Ken K

[jb123]

ive never heard of one sticking closed, so i assumed he meant open. also there should be more than one reed so if one was sticking, the others should still work correctly.

[sonat]

first of all, thanks for your prompt replies. I did also,in checking what's going on with this thing, remove the jet from both carbs to see if there was fuel in them and there was fuel in both cards. I have used ring free in almost every tank of fuel I have run through this engine. my tank hold 12 gals and I normally add 1 oz of ring free to it. but I have never done a shock treatment and I will try that, sounds like a good thing to do. I am confussed about the reed valve having some blow back through the carb. if the reed valve was stuck closed, it looks like to me that would exsplain why the plug on the dead cyl looks dry, am I thinking wrong? this engine has two carbs the top carb serves the top two cyls, the top right cyl( facing the front of the engine)is working fine but the top left cyl is the dead one. not sure but it looks like the fuel jet for the dead cyl could be plugged up not letting it get any fuel or is there just one main fuel jet in the carb serving both top cyls?. but the oil is injected below the carbs so if the reeds were working right I think I should be seeing at least some oil on the plug but the plug sure looks dry of anything. One thing is probably for sure this engine is 15 years old and the carbs are likly ready for a good cleaning. any input you guys can me will sure be great, thanks for your help.

[sonat]

P.S. does anyone know where I can get a good shop manual on a '92 model 115 Yamaha outboard engine?

[slim]

yeh you need to tesr your carbs down. there are two main jets in each carb. one on each side of the bowl at the bottom. if your not getting any fuel, then the little bit of oil that is getting in is being used to lube the cyl. in there wont be enough to get on the plug on top of the heat burning the tiny bit left in the cylinder. you dont have a stuck read valve. infact, i believe there are 4 or 8 valves on this motor per cylinder. i cant remember. tear the carbs down, go to a auto parts store and get some carb cleaner that you soak the carbs in. this is better then any spray you can get. soak all the jets and bodies of the carbs minus any rubber o-rings like the red ones on the main jets. do not soak the needle valves. they have a rubber tip. also dont forget to remove the o-ring that holds the choke spring on. soak for one hour, remove and rinse thoroughly with water and then blow out all passages thoroughly with compressed air. i like about 125psi. reassemble, resynce and run-up. you should be ready to go. your 10 psi difference in compression is probably due to a dry cylinder so clean the carbs and spray a shot of 2 stroke oil in the cylinder before you fire it up. let me know how it turns out.

[sonat]

thanks to all for your input. knowing now that are two main fuel jets, one per cyl,the carbs do indeed sound like the problem. I mean after 15 years of great service I think it's about time.

[sonat]

well you guys called it right. I pulled the top carb off and disassembled it and the main jet was plugged off. guess now I will give it a majior tune up. thanks for your input.