Hi, my ST155 does not want to start, it JUST sparks up, shakes a bit and then dies. I am not sure if I should prime it more, or could it be flooded? I was using it a couple of hours ago and it was fine, started first time - but now nothing. Have tried both warm (a while ago) and cold starts...Flooded, not primed, carby, air filter, fuel filter - not sure. Can you advise please..thanks, Max

Hi Todd:
Here's a couple of things I would do.
1) See if there is a drain plug on the carb, If there is, drain it so that you will be getting fresh fuel into it.
2) Remove the air filter cover, then remove the air filter make sure it is clean. Replace if it's really bad.
3) Squirt a bit of fresh gas into the throat of the carb, put the air filter back in place, and try to start. Usually it will be good and run. If it doesn't, youre not getting spark. If it runs a bit and then dies, you're not getting gas. Try the prime trick a few times. If it still won't keep running you'll need to take the carb apart and clean it.

Sounds like fuel pump probs if you have no spark.

Check your choke prime bulb and carburetor lines - sounds like its clogged and gas is barely leaking into flood the cylinder

Your fuel pressure regulator is bad. It is a small round 2" diameter component with a vaccuum line connected to it. If you remove the vaccuum line ane have any hint of gasoline in the hose the diaphram is bad and needs replaced. It is located on top of the engine connected to the fuel supply rail. Hope that helps answer your question. Thank you.

Prime away... on a chainsaw it does NOT squirt fuel into carb. It draws fuel from tank, through carb, and returns it to tank.
Using the choke however will flood it in a second once it has fired. with a good fuel supply, 99.5 % of chainsaw won't start problems are flooded. Lou

The pressure regulator is bad,it is allowing the fuel to pass threw to the cylinders,replace the regulator,and a new set of goos spark plugs.This is the fuel pressure regulator.

there are a few things that would cause that wo all i can tell u from what u said is that u need to check for fuel pressure w/ a gauge then look up the specs online. if u lose pressure after start up the fuel pump is bad. but if it stays good as the truck dies then u do have other issues that someone would have to look it over. u could have a ignition module heating up and opening the circuit or an electronic coolant temperature sensor reading -40 or 300 starving or flooding the engine with fuel pull out a spark plug and ground the threads onto something. and check for spark as it dies. if it stops sparking then u need to look into the ignition system. if it does not then you are looking at a fuel problem or a cam positing sensor. which could shut off fuel injector pulse and ignition fire. like i said alot of componets could cause irratic behavior like this ull just have to start off with the basics fuel and fire before you can jump to any conclusions. oh and fuel filters would cause the engine to run bad but not kill it all at once and keep it from starting. one way to rule that out is to turn the key one for 2 secs then off for 6 secs and repeat a few times this turns on the fuel pump for priming iu the system. if it still does not fire up then somethin else is going on other than the fuel filter.

sound like intake leak. get a scanner to see if egr valve not staying open . check map sensor + make sure the vacuum line didnt come off it . check coolant sensor. oxygen sensor .check fuel pressure regulator. check vacuum line that goes to fuel pressur e regulator . make sure there is no gas in it. make sure its getting vacuum. check pvc valve.shake it make sure it rattle .

Change The Spark Plug

If the starter fluid worked for a little and the engine died again, it may be some of your filters. Check the air and fuel filters and replace them if they are dirty or haven't been replaced in a long while. This is the most common reason a car won't start.

Another idea is the engine may have been flooded. If you have a fuel injected engine, don't pump the fuel when trying to start it. The fuel pump primes the engine all on it's own. If the engine is already flooded, push the fuel pedal all the way to the floor and hold it there while you try to start the engine. This bypasses the priming and opens the air to blast any unburned fuel out of the cylinders.

Check to make sure you are getting spark with an inline spark tester (at auto parts stores) and if not try replacing (in order) the spark plugs, wires and (depending on your engine) the magneto's or distributor cap. Ask the auto parts store if they can look up if you have a distributor-less ignition or if you have a distributor.

So, first the filters (air and any fuel [there may be more than 1]) then check for spark and replace the spark plugs, wires, and magneto/distributor cap.

I hope this helps and good luck! Don't forget to rate! Thank you!