Does it have a fuel pump? yes the diaphragm inside the carb. is the fuel pump, when the pistion goes up and down it acts on the diaphragm through small passages and that action pulls the fuel from the tank.

**Your problem is probably a dirty gummed up carb. which is blocking the small passages restricting the fuel through the carb.**

I would squirt carb cleaner down the carb. and try to start it. it should run off the carb cleaner till it gone. Do this several times, maybe you will get lucky and it will clear the carb. If so add carb. cleaner to the gas tank so it will clean it from the other side (internal) of the carb.

If that don't work particle disassemble and cleaning of all the small passages you can get to maybe be required.

If that don't work you may have to manually acutate the fuel needle valve and determine it's not stuck and inspect the diaphragm for stiftness? If that don't work an rebuild kit maybe in order, you can find what carb. you have by finding the letters and numbers stamped on the carb. body. wtXXX, waXXXX? ect...(the xx's will be number's warblro, caXXXX, cuXXXX? zama ect...) goggle warbro or zama for rebuild instructions.

Thanks, will give it a try

I found a crack in the impulse line next to the impulse component, I cut 1/4" off line and reinstalled impulse part.
I checked fuel line without removing it and it looked ok.
I removed filter to see if that was the problem.
Now it won't start. I shot some carb cleaner into the carb and nothing happened. not even a pop.

pulled spark plug attached wire, grounded plug and pulled starter rope last night in the dark had spark.
Switched plug from MS255 saw and put in my 046 saw and the 046 started ok.
Is there a way to test the impulse?

I have a Stihl 250 and it is the worst saw I've ever owned. Yes the impulse line cracked -- all along its length it deteriorated before 2 years of light use -- multiple cracks. Gas line, too. Obviously defective design and materials. And yes it starts for 10 seconds or less, then stops as a result. It is very difficult to replace these and get things properly back together. To the OP, when you re-installed it you must have created another problem, not unusual.

Other problems with my saw:

It leaks gas through the gas cap. This wrecks whatever you put it on.

Why does it leak? Because it has been redesigned by vaunted German engineers to look nothing like a real gas cap which used to have screw threads. No, Archimedes invention wasn't enough, it had to be specially re-designed by urban ad men for Stihl. It's an odd shaped black and white plastic thing with a lever which needs to be located about 45 degrees in rotation, the lever snapped shut and then checked. Even closed properly, mine leaks gas and oil.

Same for the bar oil cap. It MUST be checked because it can look closed even if it isn't. Nothing like pouring a tank of bar oil down your right pant leg in the woods in winter. Guess how I know?

Oh, forgot to mention, the bar oil cap though similar, is offset differently than the gas cap. Seems perfectly designed s well to drag sawdust down the keeper string when you close it up. Other saws use plastic bands or even ball chain for the keeper, both of which can swivel in the tank, and be controlled when re-capping, but not Stihl -- they think a cast in the cap kinking piece of black thread is a design advancement.

Be sure to buy a special new gas can for this saw, too, if you own other saws, because it uses expensive high test, not regular gas. Be sure to fill up with both kinds when you stop at a station, a task to add to the list, and don't mix them up.

Stihl used to be a good name back when I was a tree surgeon in the 70's - that's why I bought this one as a homeowner now -- I also own Husqvarnas, but Stihl is just pretty looking junk now -- do-nothing design engineering with a premium price tag. Labeled "occasional use" despite the fact that it costs as much as a good saw. I suppose as an excuse for leaks and breakdowns.

No thanks, Stihl, I'll get a rebuilt Poulan at half the price if I want a saw to last a year and a half. Or a Husky if I want to spend top dollar on a real tool for the long term.

Try a 270 or 290 Farm Boss ifin you want an even worse Saw lol !

If you you found a crack in your impuse line, you probably need to replace all of the fuel lines because there are probably more cracks that you can't see. Also, remove the carb and disassemble it. Take both covers off and spray every passage with carb cleaner. If the diaphragm is still flexible you can reuse it.

Watch this tear down video on youtube if your not sure how to remove the carb. its not hard to do.

http://www.youtube.com/watch?v=0m22-0Vo6Ic&feature=related

I just bought a used BG55 blower on ebay that the owner got rid of because it wouldn't run and the dealer put a new carb on it and it ran for a few weeks then wouldn't start. Picked it up cheap and put a new fuel line and tank vent because it was really clogged. Once the fuel line was put on, I readusted the carb to factory specs and it runs like it was brand new.

Just for the record, I had the same kind of problem, ran fine at idle but bogs and quits within a few seconds of high speed, and it was the fuel filter.