Echo PB 251LN Will Not Fire

[oli]

I have an Echo handheld blower, PB 251LN, serial# P34712065726, manufacture date August 2012. Compression is good, 120 psi. Exhaust port and muffler are clear. New plug-tried several. Piston looks good from both the exhaust and intake side-no scoring. Flywheel is tight and no indications that key is sheared. Coil is adjusted properly. I have swapped out the flywheel, and ignition coil with known good parts. Good 1/4" spark with adjustable gap spark tester. This blower will not even fire or pop by squirting fuel into carb. I even tried starting fluid with ether. I believe the problem is related to timing, but do not know where to look next. Is it possible that the output shaft could have rotated out of time where it is attached to the crank arm? Does anyone know if Echo has issues with this particular piece of equipment? Thanks in advance.

[bgsengine]

plug wet or plug dry after trying to start? if wet, could be flooding. doesn't take much to flood em out then you have to clear the flood (including any gas in crankcase) - poorly adjusted or leaking carburetor could be a root cause.

[oli]

I routinely use starting fluid, or gas from a spray bottle to diagnose problems with non running equipment. Carb has been removed, and I am spraying directly into the intake port and know it doesn't take much. I will check and verify if I am flooding the engine, but I don't believe I am. I have also verfied the kill switch is working properly. Thanks for your response.

[KE4AVB]

Just thinking out loud... It could be a blown cylinder or crankcase gasket.

[Skywatcher]

Hi Oli

Assuming this unit is a two cycle engine, how's the crankcase compression? Are you getting good transfer from the crankcase up into the cylinder? I've seen two cycle engine come in with wrong intake gaskets between crankcase and carburetor allowing crankcase compression to be lost through pulse port. I've also seen Stihl chainsaws with a cracked or broken pulse line dumping crankcase compression, so not getting any transfer into cylinder. Let us know what you find,

Sky

[oli]

Yes, this is a 2-cycle engine. Unit was a not running when I received it. Cylinder pressure is good-120 psi. Crankcase compression is a new term for me. How would I evaluate that? Unit was very clean when disassembled, no indication of leaking seals or gaskets. I will seal off the pulse port the next time I try to to get it to fire. I am contemplating the purchase of a pressure / vacuum tool to perform pressure / vac test, but don't know how soon that will be. Thanks for your response.

[bgsengine]

crankcase "compression" meaning the pressure/vacuum pulse caused by movement of the piston. This positive/negative pulse pressure is what is used to operate the carburetor's fuel pump diaphragm. It MUST be air tight or those small pulses bleed off. AND, the crankcase must also be air tight (and vacuum tight) because otherwise it will suck in unmetered air that mixes with the fuel charge and causes lean fuel mixtures. Did you try putting a small charge of gas into spark plug hole? (less than a teaspoon) and see if it will fire that charge? if it will, then the fuel that you are introducing through carburetor is not getting to the engine properly, which is why Sky asked if crankcase pressure had been verified. Did you use all new gaskets on assembly? how far was it disassembled? even the tiniest scratch on a gasket surface can lead to a vacuum or pressure leak, as can hardened or failing crank seals. A pressure/vacuum tester would be a MUST-HAVE investment for anyone that works on 2-strokes regularly, along with the know-how to perform the leakage tests.

[Skywatcher]

Hi Again Oli

One very quick and simple way to get a feel for crankcase compression, although no where near as accurate as pressure testing, is what I call the "Transfer Pop Check". Remove the sparkplug and turn the ignition switch off or ground the plug wire so you don't fry the ignition coil. With the choke off and throttle wide open, pull the starter cord briskly a few times. You should hear a crisp POP from the sparkplug hole on each revolution as the piston uncovers the transfer ports releasing the crankcase compression into the cylinder. If you do not hear the popping sound as the engine is spun over, you'll need to dig a little deeper. Hope this helps points you in the right direction,

Sky

[oli]

I previously posted about this unit, and the fact that it would not fire even when gas was dispensed directly into the cylinder. Compression, spark, exhaust port, and muffler were all good. Flywheel was tight. Among the suggestions received was to perform a crankcase pressure / vacuum test. I did not have the tools to perform this test at the time, but have since acquired them. Crankcase pressure / vacuum tested good. With nothing more to test, I focused on the ignition module. I contacted Echo and learned that the ignition module for some manufacturing dates failed prematurely. Unfortunately, too much time had elapsed for a warranty replacement. I ordered an aftermarket module and installed it. Unit started within a few pulls. Despite having a very strong spark, the ignition module was defective and out of time. It would have been a lot easier to diagnose if the ignition module failed completely and there was no spark, but that was not the case. Thanks for to everyone who responded.

[KE4AVB]

Yes I have seen ignition module to fail this way. IT rare but it does happen so when troubleshooting you got to keep an open mind about can the cause of the failure to run.

I once had a Homelite chainsaw where the ignition would set the paper air filter on fire at times. I had igniters to not fire on compression stroke but work fine on the wasted spark. When that did happen the first time in the shop I though someone had fired off my 12 ga and the next time it cause a foot long flame out of the exhaust that nearly set my pants leg on fire.