Stihl 020T "lumpy" to turn over, won't start.

[PatrickIreland]

Over the weekend, my 020T decided it didn't want to pull over smoothly any more. When I pull the recoil, it seems like it's trying to force past something on each compression stroke. So it's more like a "Chunk, chunk, chunk" when I pull it.
I only had a minute to check it (no free time!) so tried a spare known good recoil assembly I had - no change.
It's not the chain brake, and with the side covers off it can be turned over by hand easily via the fan.
It hadn't been used for a while, but had been run to empty before, so not a stale fuel issue.
Started up fine with new 50:1 mix, then after I turned it off, it started this malarkey. No bar or chain on it at present.
I do have a spare (new) slug and jug for it if needed, but before I start to tear it down - any pointers as to what I should be looking for?

Thanks in advance,

Patrick.

 

[KenJax Tree]

Pull the muffler and take a peek at the cylinder and piston

 

[blsnelling]

Pull the spark plug and see how it feels. Lumpy can be the flywheel magnets going past the coil.

 

[PatrickIreland]

Pull the muffler and take a peek at the cylinder and piston

Yep, that was going to be my next step... just wondering if there is a common cause for this that is easily fixed!

 

[PatrickIreland]

Thanks Brad - do you mean the magnet actually making contact with the coil, maybe due to a dead bearing? I'm not hearing any noises, and it is VERY "chunky" - not what I've felt from any of my other saws (mostly 041AVs) - it won't even "drop-start", or should I say, "drop non-start". Almost feels like it has FAR too much compression.

 

[Bilge Rat LT 20]

Is it flooding?

 

[67L36Driver]

Is it flooding?

+1

Needle/seat in the carb leaked and vapor pressure in the tank forced fuel in. Had a MS440 do that and wouldn't turn over the next day.

 

[PatrickIreland]

Afraid I didn't get a chance to look at it last night, gents, nor will I tonight - but surely the tank cap is vented to prevent pressure building up - or is it a one-way vent, to allow air in as the mix is used up?
I think my first plan of attack should be to drain the gas, take out the plug and pull it over a good few times to get rid of any excess fuel, in case it is flooding.
Interestingly, my boss has one of these cheap copies of the Stihl Kombi system (hedgecutter, strimmer, polesaw, etc) which was exhibiting exactly the same symptoms - I pulled the plug, gave it a few pulls over, then reinstalled the plug - it pulled over smooth as anything, and started straight off. I put that down to a dodgy Chinese carb, which I intend to replace.
So is it possible that pressure can actually build up in the tank, and force it through the carb? As I said, I thought the tank was vented - but maybe it's only vented to let it pull in air, not let out excess pressure!

Many thanks for all your replies,

Patrick.

 

[67L36Driver]

One way vent. Lets air in to replace space of spent fuel.

 

[PatrickIreland]

Ah, that would make sense - I store the saw in my front porch (Ireland here, so it is glazed in, not an open porch!), and the sun hits it first thing in the morning so it is a bit of a greenhouse, and we have had a lot of sun recently (more than we got in the summer!) - that would no doubt be enough to push fuel through the carb into the cylinder/case. I shall make sure it is unflooded and try it again, thank you!

 

[PatrickIreland]

VERY short update - pulled the plug, looks fine, pulls over nice and smoothly. Have left it to see if anything drains out - so I think I can rule out magnet-coil touching action.