I already found some crud in the little sump on the tank plus found a plastic piece in it also. I'm gonna take the tank off again and see if I can get some fuel flowing. I have a suspicion the valve is the culprit. I sure hope they still sell a rebuild kit for those.
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Magnesium decks?
- Thread starter parkboy
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Export threadI tried to get mine running again today with no luck. I cleaned the tank, put a new fuel line on it and got it so fuel flowed good out of the tank with the valve open. I then took the carb off again and cleaned it and checked the float level which was fine. I blew through the carb inlet to make sure the float valve was working right and it seemed to be. I put it all back together and it did the same thing, running for about five seconds and quitting. I tried it without the air filter with the same results but I did notice some fuel settling where the filter was, don't know if that means anything or not..I work on two stroke engines all the time but have to admit this one has me stumped..
Well at this point I think I would check compression, not much else it could be. Sounds like maybe you have enough vacuum to draw the fuel from the carb throat, but not enough to make the venturi pull it through the nozzle. Seals or rings could be the culprit. A leak in the crankcase, or an air leak at the carb flange could reduce the vacuum as well.
I checked compression some time ago and it was kinda low but still in the usable range but I can try checking it again. I installed the lower crank seal last week because I've heard that one goes out first but it appeared to be okay, may get around to the upper one soon. I sealed the carb flange to the engine so I don't think that's it. I kinda ruled the ignition out but not even sure about that. It is like the fuel isn't going from the carb bowl into the engine. Doesn't it just suck it up the tube that's in the bowl into the venturi? I've checked it and the passage is clear. The reeds look good from what I can see. I've also checked the exhaust ports and the muffler and didn't see anything blocked..
Yes the fuel is drawn up through the nozzle in the carb, but not directly. When the air being drawn through the carb is at a sufficient velocity it creates a venturi effect and draws a sufficient amount of fuel/oil mix up to the throat of the carb via the main jet/nozzle. Air leaks anywhere in the system will take from the required velocity to draw fuel up into the throat. These 2 strokes are very simple by design, but not as forgiving when it comes to leaks. 9 out of 10 times when one of these 2 strokes will run on primer only it is due to a clogged carb nozzle, but since you say it's been cleared 100% then I would lean toward crankcase compression being the culprit. Recheck the seals, upper and lower, it's not uncommon for those to just completely pop out on you.
Yep, I've worked on hundreds of chainsaws but not too experienced with Lawn Boys. Chainsaws that will run with a prime will generally keep running if the fuel system is okay but I'm not seeing that here. I'll go out and check the compression in a few minutes but the Lawn Boy doesn't look like it will lend itself to a pressure/vacuum test like a saw will because of the muffler but I might be able to make a plate to go over the intake and exhaust and do a pressure test on it..
I just went out and checked the compression on the mower, it measured just above 110 psi cold, after about 5 or 6 pulls. Not that great but I've had them run on less, especially the reed valve engines but I guess it could still have a crankcase leak.
I've made a kit to check crankcase pressure in chainsaws, all I need to do is make a couple of block offs for the LB and I'll be able to test it. Should be cool enough to work out in my little shop in a couple of days. I'll let you know how the test came out. I haven't done any work around the crankcase but I guess a seal could be leaking. I have plenty of soapy water to find out where the leak is!
Also I have a decent running Lawn Boy with a steel deck which doesn't get used much. The engine looks a little different or is it just the aluminum plate under the engine that is different? If it's possible to put that engine on my 19 I might do that until I can get this one sorted out.