Unable to start MS170 so advice needed for me to rule things out

[ipbr21054]

End of last season i was unable to start my MS170 so i left it until the new year when its going to be used again.
Looking in the port when carb removed i could see some scoring on the piston, probably as my mix used is 40:1
So ive decided to just fit a new complete engine unit, see photo attached.

Swaped it all over no problem.
Set gap between coil & magneto with business card.
New carb fitted.
Carb has 1 screw so i turned this left hand threaded screw so it was just seated & then back out 2 turns, this should get it started at least & i then just have to adjust it for tick over / chain spinning on bar or not.
New plug fitted.
New air filter
I mixed 1 litre of fuel then added Stihl 2 stroke oil up to the 50:1 mark & gave it a good shake.

I have held the throttle lever & then pushed that black lever on the left all the way down which i think now locks on the choke.
Pulling & pulling & nothing not even a backfire or splutter as if it wants to start.
I removed the plug & squirted a drop of carb cleaner in bore but still wont start.
Plug is getting wet.
Unable with my tool to see in this light if spark is present.
The 2 wires on the coil ive removed one at a time & tried to start to see if anything was being bypassed etc but still no start.
Ive checked that the black wire with brass fitting on the end isnt touching that metal part so when lever is moved up it makes a connection & kills the engine.
This wire goes to a spade terminal on the coil.
The other coil wire has a ring fitting & goes to earth via the top coil mount & engine cylinder.
Just ordered a new coil & awaiting it to arrive in a day or two.

Is there anything in the mean time i can be looking at / checking

Thanks

 

[Harry Bloomfield]

Plug is getting wet.
Unable with my tool to see in this light if spark is present.

If the plug is wet with fuel, but not firing, that suggests no spark.

Some vertical markings on the piston, are to be expected.

 

[ipbr21054]

I agree with spark
Lines of piston were maybe more than expected

So coil is ordered, anything else spark related i can check ?

 

[jj4091]

Have you tried to start it with the stop switch disconnected. Have you carried out all the other checks in the manual https://cdnassets.stihlusa.com/1654020968-stihl-ms-170-stihl-ms-180-owners-instruction-manual.pdf

 

[ipbr21054]

The stop switch being the black kill
Wire to coil ?

If so above mentioned it yes.

 

[ipbr21054]

@jj4091 which section you referring to in the pdf ?

 

[jj4091]

The stop switch being the black kill
Wire to coil ?

If so above mentioned it yes.

Not sure what colour it is according to manual it says STOP . If the lead runs from the coil to the engine body via the switch and nowhere else then yes that is what I would disconnect.
Page 40 onwards.

 

[ipbr21054]

It is the wire mentioned above.
The yellow wire is mounted to the top of the coil & travels down to a connection.
The black wire goes to the coil itself & also travels down by this connection.
The connection between the two are made by a spring like piece of metal that it attached to the chock lever.

When i tested it yesterday i was hoping by pulling the wire off the coil itself would allow the saw to start thus bypassing this wire altogether should it be shorted to earth along its travels but that was not the case, hence why i ordered the coil.

Ive just done a continuity test between the top mounted wire & the wire directly to the coil then operated the choke lever & my metre reacts each time so i know that side of things are working.

Now need to find out & check coil itself

 

[ipbr21054]

Anybody know about checking the coil ?

Meter set to 200 ohms
Connection from coil metal body to kill switch spade terminal
My reading is 02.2
Primary Winding

THEN

Meter set to 20K
Connection from coil metal body to plug lead inside cap
My reading is 10.16
Secondary Winding

Like shown in photo

 

[ipbr21054]

Whilst im waiting i noticed when the choke is set to be on the flap isnt shutting 100% so ive bent the metal rod a touch so now it does.

 

[Burnerman]

I don't suspect an ignition problem at all.......but try looking for a spark in complete darkness if possible.
The single screw is idle speed, not mixture.
Personally I'd be looking for a replacement carburettor - these ones aren't noted for reliability!
John

 

[ipbr21054]

The photo shown was from internet as i put it back together.
New carb was fitted same time as engine
First post mentioned once running i would set this screw for tick over

Why do you say not ignition ?

 

[Burnerman]

Obviously I don't know what is the matter with your machine.
However, coil failures are very rare - at least with genuine ones, don't use a pattern part here - and the spark is very small, hence looking for it in the dark.
The cut out mechanism isn't good, so disconnect any other coil wires for now.
I've found with faulty coils there is no resistance reading anywhere, but the resistances vary tremendously.
As you've found, full choke is necessary for a cold start.
Where are you up to now?
John

 

[ipbr21054]

Just typing as you replied.

Brought saw inside house, nice dark room.
I can see a spark.

So carb is a pattern item as original was ££££
I don’t use the saw all that much but when I do i need it working and a £££ original doesn’t make sense.

Pattern carb has left hand thread so all the way to say closed and 2 turns out but won’t start.
So I started again 1/4 turns out & tried to start but nothing.
Continued to about 3 turns out but could just see fuel under carb so it’s flooding.

I was using two different plugs due to flooding etc and other drying.

Even when dried out a squirt of carb cleaner in plug hole then plug back in still wouldnt start it.

 

[Burnerman]

Try with the screw fully in, but before you try for a start again, take the plug out, up end the engine and pull the recoil to clear any fuel away.
John