Husqvarna 435 cylinder/ piston fault or something else?

[spudulike]

On 30/12/2020 at 20:32, DaveyCrockett said:

There was a little debris in the strainer,  nothing horrendous. 

Did you mean -  both flywheels and coils CAN be faulty?

No, I don't know the history of the saw or where the parts came from but in my world, flywheels rarely fail, the most common issue is the key getting sheared off and have had one Poly flywheel lose its magnetism by being bashed against the coil as the gap was incorrectly set.

Coils are generally reliable but have seen some pretty strange issues such as no spark, spark but not under compression. No spark at all, sparks for a couple of seconds then nothing, spark at idle and dying on any throttle (very weird, probably the ignition advance circuit), spark on idle and mid revs but like the limiter is on at 7000rpm when the throttle held open.

How is the coil/flywheel gap set on your saw? If the gap is too large, it may be giving you these issues.

[DaveyCrockett]

2 hours ago, spudulike said:

 

How is the coil/flywheel gap set on your saw? If the gap is too large, it may be giving you these issues.

I didn't measure gap before removal, but it looked sensible. I set it at 0.3 mm putting it back.

A new module is on order. I will report back the outcome.

You have had some pretty weird issues over the years. It seems like all the testing methods for ignition modules are not 100 %. What do people regard as the most reliable tester and is there a better way?

[htb]

Substitution with a known good one, if you are in fortunate position to have one, which is not much help to you.

[adw]

A genuine unit I hope.

[peatff]

15 hours ago, spudulike said:

spark at idle and dying on any throttle (very weird, probably the ignition advance circuit),

 

I had one do that and it had the cleanest carb anywhere till I tried another coil. Very perplexing.

[spudulike]

On 02/01/2021 at 09:31, peatff said:

 

I had one do that and it had the cleanest carb anywhere till I tried another coil. Very perplexing.

Same here, had the carb apart three times as it was just like the high speed circuit was blocked and pulled the coil off another machine in the end and bingo. 

These modern coils often have different levels of ignition advance for starting, low revs, mid revs and flat out. In this case, I would say that the coil had blown the last one or two stages of advance hence this issue.

 

[adw]

Said it from day one, i have to confess it's probably the cheapest unit they could possibly of found.

[DaveyCrockett]

On 03/01/2021 at 20:01, adw said:

Said it from day one, i have to confess it's probably the cheapest unit they could possibly of found.

New genuine ignition module fitted and it's running pretty good.  Max RPM a bit slow and it has a little hesitation on acceleration, but a tune up tomorrow should see it right.

Thanks to everyone who contributed to the thread, especially ADW who's diagnosis was spot on.

DaveyCrockett

[spudulike]

Damn...ADW will never let us forget this.....ever😭

Glad it is sorted....lets hope it stays that way....for a long time!