I have a os 25 that was given to me from a friend but it as a problem. It will stay running as long as i leave the electric starter on it but as soon as i take it off it will only run about 5 sec. I thought maybe is running to rich but i dont know. What glow plug should i use in it?Thanks for the help.

That's a new one (keeps running when starter is on)? Anyhow from what you say sounds like a bad glow plug or no fuel. It can be a b-t working with an old engine since you have no idea what previous owner as done. Any glow plug should usually work as long as you know it glows brightly. With needle valve opened about 2-1/2 turns choke it till you see fuel at carb. Connect glow plug but do not use starter at this time. Hand start carefully ( use a chicken stick). It should at least fire several times maybe even start. At this needle setting it should be a bit rich so adjust for smooth running. If it quits then you may have a fuel problem or clogged fuel valve. If running decent then try adjusting idle. You failed to mention what engine you have but if air bleed open air hole slightly to lean out close to richen. If separete idle screw close to lean open to richen.Tuning an engine takes experience so get help if possible.

It probably dont gets enough fuel. The starter will work like a fuelpump. when you crank the engine with the starter it will suck fuel from the tank and reach the carb. And when you turn off the starter it wont suck fuel anymore. So, turn the full speed needle completely in, and then out again about 2-2,5 turns. If the problem still occurs then I dont know. I had a similiar problem once. You should also check the fueltank and the fueltubes for leaks, and clean the carb.

Theses are great little engines

SOund like it need some tlc

Your gonna need to pull the carb and clean it. usually I'd say rtv it when you put it back together but I've never had to do that with an OS.

change the glow plug and cheack the fuel tubing and tank.

With the glow igniter off and throttle wide open. hold your finger over the exuast and flip the prop. After 4-5 your should see fuel pumped to the carb.


Set the low screw so the head is even with the outside of the carb body, then screw it in a full turn. set the high end. Screw it all the way in then unscrew it richen it 2 1/2 full turns. It should run at that setting. set the radio for a high idle and move the stick up 4-5 clicks. add the igniter and start it. It should run. if not lean the high end a half turn. if it winds up, runs for a sec and dies richen the high end a half turn

go the full throttle and lean the high end screw until it peaks in rpm then richen it until you hear a slight rpm drop. drop it to idle. it may die just restart it at a higher rpm. pitch the fuel line. It sould run for 5 sec and die. If it speed up and dies it rich. lean out the low end. if it just dies it's lean. richen the low end.


reset the high end. reset the low end. let it idle about 30 sec and go to full throttle. it shouldn't hesitate. if it hesitates lean the low end. if it dies richen it

do this 3-4 times.