550xp in the workshop

[billpierce]

Pal has given a 550 to fettle. Won't start. New plug, good strong spark, clean air filter, good comp.

 

Before I get started do I need to treat anything differently as it's autotune? Not worked on an autotune before. Is there a reset button on the carb? As it doesn't seem to be fueling.

[spudulike]

Check the state of the piston, do all the normal things you would on a non AT saw as they often are the things that fail on AT saws. You can spray carb cleaner down the carb and see if it will fire but would do the compression and piston check before going too far.

No reset button on the carb, the saw should fuel and flood if you pull it over on full choke a few times. Check the gauze filter and metering arm, same as on a normal carb - they aren't that different!

[billpierce]

Check the state of the piston, do all the normal things you would on a non AT saw as they often are the things that fail on AT saws. You can spray carb cleaner down the carb and see if it will fire but would do the compression and piston check before going too far.
No reset button on the carb, the saw should fuel and flood if you pull it over on full choke a few times. Check the gauze filter and metering arm, same as on a normal carb - they aren't that different!

Great thanks. Gave it a quick squirt of carb cleaner just to see if I could get it to fire...no luck.

I will pull exhaust/ compression test next.

Ta

[outinthewood]

I have run and owned three 550's a great saw that can do some odd things, Just asking the plain basic- the plug is wet but still not starting ? all the wiring harness is connected and not damaged ? I don't know if there is a way of checking the fuel valve without pluging it in to the workshop software ? There is a magnet below the "Needles" which can pick up bits of debris which can cause problems but not sure on starting. When I've done the big clean I have had a no start - dash a little fuel- not carb cleaner- over the air filter and away they go. As already said they are a carb after all, you can still strip them and clean it's just they dont have needles as we know !

[billpierce]

Haven't checked wiring harness yet. Has a good spark. Not getting wet though.

[billpierce]

Did try fuel and carb cleaner and it didn't fire once both on the filter and finally a drop down the cylinder. Still nothing. I will have a play and report back....

[Sveriges]

The magnet is used for the throttle sensor and yes they can pick up all sorts of debris  from the bench. There is no way of checking the valve without activating it via the laptop but it’s very rare to have one fail. What is important is making sure the airgap on the coil is set to 0.2 and that the magnets are clean. 

 

As as stated above make sure the engine is good mechanically. If it isn’t then you need to find the route cause. I would also pressure and vac test it. You can’t repair these properly unless you know the engine is air tight  your wasting your time otherwise. With the right tools it’s a 5 minute check. Split manifolds and port cover gaskets  used to be common. The auto tune can compensate for a small air leak and they run lean enough as it is! Of course it would still start and run but when the operator has it red hot in the woods and it doesn’t restart properly or it seizes they get really pissed! 

[spudulike]

Out on the woods - If the saw is full of fuel down to flooding, do as you would with a normal saw. Remove the plug, turn upside down, pull it over hard until no more spatters out. Heat the plug up good and hot, replace quickly, put the carb on fast idle (no choke) and pull over without the decomp on.

If it doesn't start then check the plug is sparking.

It is quite easy to miss the first pop, had this a few times on certain machines and is usually just down to rebuild oil fouling the plug and the decomp lowering the compression more than the engine needs.

 

Bill - If the saw is sparking than the earth and that part of the ignition system is OK.

[outinthewood]

Who said anything about flooding ? I find that a lot of folk are "afraid" of Autotune/Mtronic it is as you said a carb that can get dirty and can be cleaned and the basic things are overlooked. There are a couple of extra wires and no needles that can be adjusted to see whats going on. I had assumed from what the OP had said he had checked the basic stuff and he made no referance to flooding, perhaps I should have said damp instead of wet in other words proof of fuel . I'm not 100% sure but the way they are wired can mean a spark but the fuel valve is not doing it's part, I'm sure a dealer can wade in on that ? In my 30 odd years of running saws as my job I sometimes forget to state everything and some of it is still in the brain not printed out ! 

[spudulike]

Sorry - misread your post, didn't see you were answering rather than having an issue