MS250 - What have I done??

[IRONJACK]

I have a 2002 MS250 that's probably done 20 hours from new. It lived in my Mums garage for years getting dusty.

I've used it on several occasions now and it's been solid, apart from sometimes stalling when cold at idle.

I was using it on Wednesday and after 10-15 mins it started cutting out and stalling at high revs, after a few more minutes it wouldn't start at all.

After successfully changing the membranes on a 200T carb, I decided to get a carb kit and set to it. While taking it apart the following day, I went to take the plug out (to replace it) only to discover it was very loose. As I already had the carb off I thought it would still benefit from a service, so I took it to my local garage to borrow an airline to blow it out on the way GHS to get the new plug and carb kit. I also took the opportunity to give the saw a good blow out.

Once home, I changed the membranes and put the saw back together.

Now it won't run properly.

Symptoms;

1 pull on full choke - will give the normal fire and die.

3 pulls on half choke - fires, revs up to about 75% then stalls.

10K+ pulls on no choke occasionally produces a stutter, lots swearing and a very sore arm!

Other info;

It slowly leaks fuel, 1/2 a tank over 3 days, but I can't see where from. (I think it must be ninja fuel)

The fuel line is a bit cracked but doesn't appear to be breached.

The fuel is actually fresh, with precisely mixed Stihl 2 stroke oil.

Since the amazing service I gave it, it has reved up fully and it ran well for around 90 seconds ish.

I did put a new, correct plug in it.

The carb was still at factory settings, I measured screwing them in 1 full turn each, then tried them screwed out 3/4 turn each but same symptoms. They are now back at 1 full out.

The idle screw has been tried in numerous positions, but I think it about where it should be now.

I took off some plastic and rubber parts and soaked them in washing up liquid. I cleaned and dried them thoroughly. Whilst starting this thread I had a brainwave, perhaps the breather pipe and/or valve was blocked with water and was creating a vacuum in the tank? So I went outside and pulled it off the tank. My arm is sore again, and the symptoms are consistent with yesterdays.

 

I'm sure if I'd just replaced or even just tightened up the plug it would be running fine now.

 

Anyone seen anything like this before? Or have any bright ideas?

Many thanks in advance for any suggestions.

[spudulike]

The dissapearing fuel is probably a leaking needle valve - the fuel is probably ending up in the crankcase and causing flooding!

 

Hope you got the gaskets round the right way on the carb rebuild!

[18 stoner]

It slowly leaks fuel, 1/2 a tank over 3 days, but I can't see where from.

 

I think this issue could be the problem and needs sorting before wasting any more time/money on other stuff.

[18 stoner]

Just read my post back, and it wasnt really too helpful!

 

Spud is correct, it could be causing flooding, but also could be drawing air.

[IRONJACK]

I'm not worried about the leaking fuel, it's VERY slow and I'll just empty the tank when I'm finished with it.

If the fuel was flooding the crank case, wouldn't I have had the same problem before my masterful service? It's been leaking fuel since I've had it, but the issues started after I dicked about with carb.

I'm pretty certain the new membranes and gaskets went on the right way round.

[IRONJACK]

So start by replacing the cracked fuel line?

With these symptoms, is it possible I've inadvertently blown (with the airline) some cack deep into the carb body?

I didn't touch the inner valves, but have spares that came with the carb kit. As they're metal and saw has done little work I thought replacing them would be pointless, and tricky. Should I swap them out?

[Tom D]

If it is leaking fuel when not running then it is probably drawing air when it is running.

 

change the fuel line.

[spudulike]

The "metal valves" you describe will either be needle valves or welch plugs, to rebuild a carb, you need to understand how it works and what each part does, the needle valve arm will need re-setting if it is replaced.

 

If the fuel is leaking to the outside of the saw then it isn't the needle valve, especially if it hasn't been replaced.

 

Actually - on reading our original posting - find the fuel leak and fix it - the starting problem is probably the orientation of the pumping gasket, the thin plastic one should be closest to the carb body with the spacer one closest to the top cover. Had a Jonsered like that once - had an arm like Popeye until I fixed it!

Check the gauze filter is clear of crap when you check it.

[IRONJACK]

I'm pretty sure the spacer and membrane are the way described, but you've planted a seed of doubt so I'll check tomorrow.

[IRONJACK]

The gauze filter was spotless but I changed it anyway, as the carb kit had a spare.