Tillotson Chainsaw carb question

[Paul Moir]

I'm having a little trouble with a Jonsered 630 that has fuel delivery problems. It's got a Tillotson HS series (218S) carb on it which had both mixture screws backed out a few turns. The saw had a mind of it's own and you had to fiddle with the mixture controls constantly to keep it running.<br />My question is about how the diaphram in the 'bowl' works. The way I understand it, when the fuel quantity drops in that chamber, the diaphram is supposed to collapse and open the inlet needle to let more fuel in. But on the one I've got, the spring that closes the needle valve is preventing it from opening even with the chamber empty. Is there supposed to be some sort of spring or something that pushes the diaphram in? Or is the diaphram supposed to be springy enough to act against the needle's spring?<br /><br />Mabey I'm misunderstanding how it works though... <br /><br />Thanks to anyone who can help!

 

[Scaaty]

Re: Tillotson Chainsaw carb question

diaphram supposed to be springy ..at least I think. Try a new one if you can get one.

 

[Paul Moir]

Re: Tillotson Chainsaw carb question

Thank you very much Robby6950!<br /><br />This one's definitely gone all limpy then. In retrospect this makes sense - earlier this year it must have gotten some bad gas, because the fuel line melted into nothingness. After I replaced it, it still never ran right even after cleaning out the carb. I guess the diaphragm took it too.<br /><br />I just found some diagrams online that indicate no separate spring (Chain Saw Info). I'll try getting a carb kit tomorrow for this thing. It shouldn't be much trouble - seems like they're pretty common and the saw isn't very old.<br /><br />Thanks again!

 

[Paul Moir]

Re: Tillotson Chainsaw carb question

I picked up a carb kit today and just finished buttoning it up. Now it's running like it's supposed to - really, really well.<br />I get how the diaphram is supposed to work now; it collapses as the engine sucks gas through the jets, allowing more in. I was thinking positive pressure rather than that.<br /><br />On a related note, does anyone know why one has to pull the cord on a small engine approximately 400 times after you flood it before you realize you have? Does pulling the cord keep your brain from working or what?