Stihl 201tc idle issues

[Bensmith]

Hi everyone, my 2018 Stihl 201tc (mtronic v2 i think) wont idle, it starts cold every time and mid to top revs runs a treat but when it dies i often have to restart it on full throttle.

I changed the solenoid (the old one was black and new green) first which enabled it to do the 90sec reset (which I’ve done every time changed anything) but still no idle so next i changed the diaphragm and reed, spark, fuel and air but no significant change.

Because I changed only the solenoid first there’s a chance I blew some rubbish back into the diaphragm chamber which then contaminated the new solenoid but I have since redone the whole thing in one go with a good clean and it’s just the same

I can force it to idle by turning the “old” idle set screw that’s thread locked in the factory but it’s rough and not a permanent solution unless at extreme altitude and im at sea level.

It will idle perfectly, rev up well and not cut too badly with the pulse line off but as soon as i put any resistance over the crank side it dies and if I block the carb side it dies after a few min on idle.

If I loosen the exhaust bolts it will also idle but with the exhaust removed the idle is erratic, so I did the mod hoping it would help but it didn’t.

Any thoughts on what’s causing these symptoms would be appreciated, thanks

[Stubby]

22 hours ago, Bensmith said:

Hi everyone, my 2018 Stihl 201tc (mtronic v2 i think) wont idle, it starts cold every time and mid to top revs runs a treat but when it dies i often have to restart it on full throttle.

I changed the solenoid (the old one was black and new green) first which enabled it to do the 90sec reset (which I’ve done every time changed anything) but still no idle so next i changed the diaphragm and reed, spark, fuel and air but no significant change.

Because I changed only the solenoid first there’s a chance I blew some rubbish back into the diaphragm chamber which then contaminated the new solenoid but I have since redone the whole thing in one go with a good clean and it’s just the same

I can force it to idle by turning the “old” idle set screw that’s thread locked in the factory but it’s rough and not a permanent solution unless at extreme altitude and im at sea level.

It will idle perfectly, rev up well and not cut too badly with the pulse line off but as soon as i put any resistance over the crank side it dies and if I block the carb side it dies after a few min on idle.

If I loosen the exhaust bolts it will also idle but with the exhaust removed the idle is erratic, so I did the mod hoping it would help but it didn’t.

Any thoughts on what’s causing these symptoms would be appreciated, thanks

Have you checked to see if the impulse line is split or not connected ? 

[Bensmith]

The pulse line looks fine, at the moment it only wants to idle with the line off!

 

So I guess a question would be why would a saw run without the pulse line?

I assumed it needed the pulse to regulate the carb.

[Stubby]

30 minutes ago, Bensmith said:

The pulse line looks fine, at the moment it only wants to idle with the line off!

 

So I guess a question would be why would a saw run without the pulse line?

I assumed it needed the pulse to regulate the carb.

I think we need Spud on this one @spudulike .........

[Bensmith]

Thanks, I feel a bit stuck because with a standard carb id just up the idle and or adjust the L on the carb and it would probably work again but I can’t do that with this one other than forcing it with the idle set screw on the carb which is fine for around a tank but the mtronic seems to learn and the problem reoccurs and I up it a bit more to the point where when I set it back to “factory” after the full carb clean the screw was nearly 3 turns out.

The spark isn’t really saying too rich or lean, it was possibly a bit rich on the no6 plug so I put a no7 in it and seems a little lean now

[spudulike]

The impulse line allows the fuel in the fuel tank to be pumped to the carb ABOVE it...think of it as part of a mini fuel pump. I have seen saws run with them removed as the fuel tank generally has a bit of positive pressure in it but when this goes negative, the saw will not run.

Idling issues on these saws are more often than not, down to the solenoid...I know you have changed it.

You mention changing the "Reeds"...these saws don't have reeds..reeds allow the carb to pump fuel mix vapour directly in to the crankcase whilst sealing it once positive pressure forms in the crankcase which does away with the piston timing on the inlet port on the cylinder. Old saws may have reeds as well as old two stroke motorcycles. You may mean the pump diaphragm, when you replaced these diaphragms, I trust the spacer sealing gaskets were replaced in the correct order....the pump diaphragm should rest directly against the carb body, the metering diaphragm should have the spacer garket between it and the carb body.

Did you change the gauze strainer? This causes many issues on carbs.

Have you checked the fuel line and fuel filter? some of the Stihl solenoid upgrade kits come with the later orange (finer) fuel filter.

The exhaust can block as Stihl like to make the outlet pretty small but it sounds like you have been there.

The wiring loom under the top handle front AV mount can stress and stretch/break the wires especially if the saw has stuck in the cut at some stage and it is best to either measure the continuity of the three wires or just replace the loom. I had one saw that seemed fine but would consistently cut out if shaken violently.

Have you checked the coil to flywheel gap? 

Is the HT lead in good order? Seen plenty of saws where the spur has come away from the HT lead.

 

[spudulike]

BTW...you really shouldn't change the idle screw setting, if the saw ran for most of it's life in a set position, it should't need changing. Running a saw with the impulse line off causes an air leak and can risk engine seizure although the Mtronic should compensate for this. 

Is the piston in decent order?

[Bensmith]

Other than the lack of idle it’s a great saw, the throttle response is amazing compared to my 1978 015  and it will eat through up to pretty much any 8” log without breaking a sweat, its logged up at least 10 cubic M for me this summer and happily devoured the lot, I just wish it would idle so I can take it up a tree and be safe

[Bensmith]

Thanks Spud, lots to digest here, I think I’ve been calling the metering diaphragm the reed

It was a kit, i changed the gaskets, diaphragms and gauze but not the needle, arm or spring

The piston looks cleanish and not scored but I’ve only looked through the exhaust and plug ports.

I’ve only run it with the pulse line off for testing purposes I wouldn’t use it like that, I was surprised at the strength of the jet, I was expecting more of a puff but ill check the rest of your suggestions and get back

[Bensmith]

I'm still wrong and you're right it's the pump diaphragm I've been calling the reed.

 

21 hours ago, spudulike said:

I trust the spacer sealing gaskets were replaced in the correct order....the pump diaphragm should rest directly against the carb body, the metering diaphragm should have the spacer garket between it and the carb body.

Have you checked the fuel line and fuel filter? some of the Stihl solenoid upgrade kits come with the later orange (finer) fuel filter.

The exhaust can block as Stihl like to make the outlet pretty small but it sounds like you have been there.

The wiring loom under the top handle front AV mount can stress and stretch/break the wires especially if the saw has stuck in the cut at some stage and it is best to either measure the continuity of the three wires or just replace the loom. I had one saw that seemed fine but would consistently cut out if shaken violently.

Have you checked the coil to flywheel gap? 

Is the HT lead in good order? Seen plenty of saws where the spur has come away from the HT lead.

 

Gaskets checked and in the correct order, i tried flipping the metering diaphragm and it may have made it a fraction better but after a reset its the same

 

The fuel line, filter and tank were all given a really good clean, its on the standard white filter but running it with a much less restrictive filter its the same. I don't have a way to pressure test the fuel lines other than with my mouth and some carb cleaner and it seems ok.

 

I've opened up the exhaust outlet so when i blow through it the resistance feels about the same from each end so about twice the original size, it definitely sounds a lot happier and feels a bit more aggressive but no idle.

 

There's continuity on the red and yellow wires from the coil to the carb connector, i couldn't see where the black one terminated and completely forgot to check the carb side of it so will have to keep you posted on that one. I thought someone said a wiring fault is either intermittent or just wont work, my issue is consistent no matter how much i prod and poke those cables.

 

The flywheel gap is about .2-.3mm, my feeler gauge has seen better days but what should the gap be?

 

The plug spur is well connected and doesn't look yanked, it has a reassuring click and again holding it in or wiggling it around it runs the same. There's a slight dint in the HT lead where the retaining screw has compressed the plastic and i cant check the rest of it without removing the fly and i need to make a puller for that. 

The spark isn’t really saying too rich or lean it was possibly a bit rich on the no6 plug so I put a no7 in it and seems possibly a little lean now but well within old carb parameters on both

 

22 hours ago, spudulike said:

BTW...you really shouldn't change the idle screw setting, if the saw ran for most of it's life in a set position, it should't need changing. Running a saw with the impulse line off causes an air leak and can risk engine seizure although the Mtronic should compensate for this. 

Is the piston in decent order?

 

Thanks, I know I shouldn’t do it but I feel a bit stuck because with a standard carb id just up the idle and or adjust the L on the carb and it would either give me something to work from or just work again but I can’t do that with this one other than forcing it with the idle set screw on the carb which is fine for a while but the mtronic seems to learn and the problem reoccurs and I up it a bit more to the point where when I set it back to “factory” after the full carb clean the screw was nearly 3 turns out so clearly not a solution.