Stihl 75 Pole Saw - No Spark no start!

[Duke box]

Hi guys,

I've been trying to repair / rebuild a ht 75 Pole Saw.

It has new:
Ignition module
Spark Plug
Carbi
And has been cleaned within an inch of it's life...but the b***** won't start.

I've figured out its not sparking.

So I've got a donor clapped out ht 75 engine and handle which sparks and fires up and switched the following parts around to try work out what the problem is...

Ignition module
Spark plug
I've even switched round the throttle/stop/start handle as i read on another post that the on off slide switch can sometimes be a problem..

But nothing! Still no Spark.


What am i missing? What else could it be?

Note: I'm an accountant by trade so you may have to dumb the responses down.
Cheers..

 

[Conquistador3]

Have you checked the gap between the ignition pickups and the flywheel?
On those Stihl engines it needs to be set at 0.3mm. If you haven't got a feeler gauge of the correct thickness, an ordinary business card should do the trick, provided they don't print them on thinner or thicker paper Down Under.

 

[Duke box]

Have you checked the gap between the ignition pickups and the flywheel?
On those Stihl engines it needs to be set at 0.3mm. If you haven't got a feeler gauge of the correct thickness, an ordinary business card should do the trick, provided they don't print them on thinner or thicker paper Down Under.

Hey there. Haven't tried the business car trick but I did Play around with different gaps and nothing worked. Not sure it's that.

I've managed to pull the ignition on and off the old donor engine and can still get that one to Spark.

Is it possible there's something wrong with the fly wheel?

 

[pro94lt]

Have you checked the on off switch? Mine was causing no spark...

 

[Duke box]

Have you checked the on off switch? Mine was causing no spark...

Hi there,

I switched over a donor on off switch but still no spark so I'm not sure it's that.

Is there a way to test the switch to be sure?

 

[pro94lt]

If the 2 Metal pieces are touching it grounds it out I believe... what about plug wire?

 

[Duke box]

If the 2 Metal pieces are touching it grounds it out I believe... what about plug wire?

Sorry, not quite sure I understand that.

As mentioned, I've pulled off a working ignition module, plug and switch from another donor ht75 engine and still can't get this unit to start.

 

[pro94lt]

Well if you take the side cover off the on/off/choke switch you'll see when off the 2 Metal poles touch grounding out the spark... what I'm talking about is mounted on the pole part of the unit. Where the throttle is.

 

[HarleyT]

Take off your muffler and look at the piston.

 

[Duke box]

Well if you take the side cover off the on/off/choke switch you'll see when off the 2 Metal poles touch grounding out the spark... what I'm talking about is mounted on the pole part of the unit. Where the throttle is.

Ah yeah, I get you. Yes I saw that mechanism when I pulled the handle apart.

Thing is, when I put on the other units on/off/choke handle (which I know works) I still have the same problem I.e no Spark.

 

[Duke box]

Take off your muffler and look at the piston.

What am I hoping to see Harley?

 

[HarleyT]

Hoping to see a piston that is not badly scored...

It will take only a minute..... Costs nothing.

 

[Duke box]

Hoping to see a piston that is not badly scored...

It will take only a minute..... Costs nothing.

Piston is all good. When I pulled it all apart, I had the muffler and carbi off and the piston looked scuff free.

Out of interest, why would that potentially affect the Spark.

 

[HarleyT]

It would not. Just something to look at first.

 

[HarleyT]

Next, leave the kill wire disconnected. Then try it. It is also likely flooded.

 

[Duke box]

Out of interest, one of the ht75 motors I have has two wires coming from the on /off switch (a black and a blue). The One I'm trying to get working only has a single Black wire coming out of the on/off switch.

Any views on that?

 

[Duke box]

Next, leave the kill wire disconnected. Then try it. It is also likely flooded.

Kill wire would be the black one that plugs to the top of the ignition module.

Near 1am here so will have to wait till morning before giving it another shot.

 

[HarleyT]

All the kill switch circuit does is connect the terminal on top of the coil to ground to short circuit the coil and shut the unit off.

 

[HarleyT]

I put this up a little while ago, I don't know what happened to it. It is a pic of both versions.

 

[Duke box]

All the kill switch circuit does is connect the terminal on top of the coil to ground to short circuit the coil and shut the unit off.

Hey Harley and Pro.

You were right. Disconnected the black wire from the ignition coil and its now sparking well.

So I'm assuming it's the switch that is the problem.

Pro - how did you fix your switch?