What's on your bench today?

[spudulike]

Using your blocking the strato - this would richen the mixture so the theory is it is under fuelling so you need to richen the H screw - see what this does. It should make some sort of difference...eventually!

If blocking the strato does help it pick up revs, it shouldn't be the HT system as it wouldn't improve if it was.

Sounds like we need more fuel then!

Worth removing the air filter - it should make it worse!

[bmp01]

1 hour ago, openspaceman said:

I was tractor driving today so no time on the saw but I did get the owner to film it.

 

https://drive.google.com/file/d/1Fj4wpt50J0tp4G3w7M2q3Yp2_lWvRxhq/view?usp=sharing

DRIVE.GOOGLE.COM

I'll leave it up for a week or so for anyone to view.

 

I have not bought a new spark plug nor tried the hemostat on the line from the carb to the purge bulb.

Might be me but didn't the saw rev up, then start misfiring and drop revs ???

Agree with Spud that sounded rich at idle and the initial rev up didn't sound clear or particularly high revving. Was that from cold, any different warm?

I wouldn't rule out spark plug / ignition trouble for the misfiring from high speed. Broken plug I had on a MS211 made saw impossible to start though, plug was arcing internally through the ceramic.

 

Again as Spud says if blocking the strato port allows it to rev cleanly then its not ignition.

 

Got a 181 here if you want me to test carb, coil on it. Would need posting, Northants.

 

Last thing, this range of saws are pretty mediocre on compression from new, I've found high comp engines are more tolerant to fueling being a little out of wack. Have you checked compression?

[peatff]

Did it oil the Vitara windscreen as well ?😁

[openspaceman]

3 minutes ago, peatff said:

Did it oil the Vitara windscreen as well ?😁

Probably but not enough to notice, you would not believe how much stuff I had in the back, just to make sure I could keep two 50 year old tractors running for a few hours

[openspaceman]

11 hours ago, bmp01 said:

Might be me but didn't the saw rev up, then start misfiring and drop revs ???

Yes exactly that, if you look at my fingers you will see it seems to pick up with a slight stutter and then with throttle wide open it starts missfiring but not screaming like the mixture were weakening off.

 

With a constant wide open throttle the acceleration pump should make no difference should it?

Quote

Agree with Spud that sounded rich at idle and the initial rev up didn't sound clear or particularly high revving. Was that from cold, any different warm?

I didn't get it warm as other things to do.

Quote

I wouldn't rule out spark plug / ignition trouble for the misfiring from high speed. Broken plug I had on a MS211 made saw impossible to start though, plug was arcing internally through the ceramic.

Nor me, if you think about it with the strato port blocked even with the throttle wide open there will be less pressure in the chamber.

Quote

 

Again as Spud says if blocking the strato port allows it to rev cleanly then its not ignition.

 

Got a 181 here if you want me to test carb, coil on it. Would need posting, Northants.

How far from Wellinborough? I have a mate that does that trip once a month.

Quote

 

Last thing, this range of saws are pretty mediocre on compression from new, I've found high comp engines are more tolerant to fueling being a little out of wack. Have you checked compression?

No, since I retired I have no accurate means of pressure or vacuum testing.

 

The big problem is that even though this is a 11 year old saw  the current version is only £270 so apart from my time, which is free, there's a limit to which it's worth going.

Edited February 7, 2022 by openspaceman
added question

[bmp01]

3 hours ago, openspaceman said:

Yes exactly that, if you look at my fingers you will see it seems to pick up with a slight stutter and then with throttle wide open it starts missfiring but not screaming like the mixture were weakening off.

 

With a constant wide open throttle the acceleration pump should make no difference should it?

Ah ok hadnt related throttle posn, thought it was all wide open throttle ...  So are you saying it will it hold high rpm on part throttle for a good length of time but as soon as you go wide open throttle it falls over? That would be consistant with your blocked strato port expt. Suggests ignition is ok but not 100% certain...

The accel pump is just a small spring loaded piston which gets pushed by a notch on the throttle shaft to squeeze extra fuel into the high speed circuit as throttle is opened. The piston is sealed in its bore by an o ring. The o ring wears, splits or degrades with bad fuel, piston and bore also wear in bad cases. So the problems arise because there is then an (small) air leak path across the accel piston into the high speed fuel circuit. Poor or inconsistant throttle response are the usual. Not sure it would do what you are seeing but then again who knows...

 

Not a million miles from Wellingborough. If your mate travels up the M1 I'm a mile from M1 Jn 16 if that helps. Can sort this out via PM if you want.  Reward is in helping fix the bugger !

[openspaceman]

3 hours ago, bmp01 said:

Ah ok hadnt related throttle posn, thought it was all wide open throttle ...  So are you saying it will it hold high rpm on part throttle for a good length of time but as soon as you go wide open throttle it falls over?

 

No in the video I rev it from tickover and hold it there, at first it seems to pick up but not quite crisply then it falters with a misfire. I said earlier it was a bit like a pea in a whistle but interfering with the fuel flow. I wonder if a series of bubbles are being pulled through the jet. Anyway there are still things to experiment with.

 

My point about the lower pressure when the strato port was blocked was not only does this richen the mixture but spark plugs sometimes fail at pressure.

 

 

3 hours ago, bmp01 said:

That would be consistant with your blocked strato port expt. Suggests ignition is ok but not 100% certain...

The accel pump is just a small spring loaded piston which gets pushed by a notch on the throttle shaft to squeeze extra fuel into the high speed circuit as throttle is opened. The piston is sealed in its bore by an o ring. The o ring wears, splits or degrades with bad fuel, piston and bore also wear in bad cases. So the problems arise because there is then an (small) air leak path across the accel piston into the high speed fuel circuit. Poor or inconsistant throttle response are the usual. Not sure it would do what you are seeing but then again who knows...

So that is a definite possibility, air bubbles in the main jet.

3 hours ago, bmp01 said:

 

Not a million miles from Wellingborough. If your mate travels up the M1 I'm a mile from M1 Jn 16 if that helps. Can sort this out via PM if you want.  Reward is in helping fix the bugger !

I'll take it to PM if it gets no further, thanks.

[spudulike]

I had similar with a 236 today...it had shyte in the gauze strainer plus the fuel tank breather was blocked.

Have you tested the breather or just removed it and tried the saw again?

Worth a punt if not.

[openspaceman]

32 minutes ago, spudulike said:

I had similar with a 236 today...it had shyte in the gauze strainer plus the fuel tank breather was blocked.

Have you tested the breather or just removed it and tried the saw again?

Worth a punt if not.

I have replaced the fuel tank weighted filter but kept the hose to outside the tank, replaced the moulded fuel pipe that attaches to it and the carb. Plus replaced the fuel lines to and from the purge bulb, I checked the in carb gauze filter and it was clean, I back washed it with carb cleaner just in case.

[spudulike]

But what about the fuel tank breather? If you are sucking out fuel, you need to let air in otherwise the saw exhibits running out of fuel symptoms.

It will look like this....pull it off and you should be able to suck air through it relatively easily. If it has sealed up, it needs replacing.

Tank Vent for Stihl MS201, MS201C - 0000 350 5802 | L&S Engineers

WWW.LSENGINEERS.CO.UK

---

Tank vent Genuine Stihl Part OEM Part No. 0000 350 5802 Suitable for the following Stihl Machines: MS 201, MS 201 C...

 

Edited February 7, 2022 by spudulike