Stihl MS211/C problem with power in the cut

[John Rainford]

This is a follow up to my post a few weeks ago which was about an ongoing flooding issue on start up. sometimes it would start and sometimes it would flood. I'm wondering if this new problem might give a clue to the issue. Once started it revs well, but when cutting, although it sounds fine, there is very little power and it takes four times as long as it used to when cutting a small log, and has no chance of cutting anything more than 10 cm in diameter. My brother used it to cut some small logs for the fire and used a tank of fuel in less than 15 minutes. I'm guessing compression issue, or maybe an air leak, but I am no expert. I would like to fix it myself and have stripped it down completely in the past so feel confident I could do so if I knew what the issue was. I was hoping not to have to pay out for compression and pressure/vacuum tests, but perhaps that is the only way forward.

[Stubby]

5 minutes ago, John Rainford said:

This is a follow up to my post a few weeks ago which was about an ongoing flooding issue on start up. sometimes it would start and sometimes it would flood. I'm wondering if this new problem might give a clue to the issue. Once started it revs well, but when cutting, although it sounds fine, there is very little power and it takes four times as long as it used to when cutting a small log, and has no chance of cutting anything more than 10 cm in diameter. My brother used it to cut some small logs for the fire and used a tank of fuel in less than 15 minutes. I'm guessing compression issue, or maybe an air leak, but I am no expert. I would like to fix it myself and have stripped it down completely in the past so feel confident I could do so if I knew what the issue was. I was hoping not to have to pay out for compression and pressure/vacuum tests, but perhaps that is the only way forward.

@spudulike

[spudulike]

1 hour ago, Stubby said:

@spudulike

No......... keep it going, we could make 2021 with this one and just giving it to someone who can fix it spoils all the fun and it is saving money.....unless you work out the time spent at your normal hourly work rate and........anyway, it is a 211, it would be difficult to keep it an economical repair especially as it has been completely apart by someone who hasn't done this sort of work before...never good!

The new analysis/info could mean anything but compression and piston condition would be my first call as it usually is when I get a machine in. anything 150psi+ would be OK, 170psi better.

 

[adw]

Makes no real sense, if it were any air leak it would be running lean, thus using less fuel, if as you say its using more fuel then its running rich, this would also explain low power. Are we sure the air filter is not blocked, or if these things have a spark arrester, is it part blocked, should have bought a T540.

[spudulike]

You can usually tell mid/bad air leaks as the machine will stay running even with the idle screw right out, that and the saw holding on to revs when the throttle is snapped shut. Probably not an air leak but if a novice has been rebuilding the saw, who knows. Were the seals inserted properly, the clam sealed with correct liquid gasket, was the coil to flywheel set correctly, was the inlet manifold and all its support rings assembled correctly? Was the piston taken off, was it put back the correct way round - seen THAT before!

Was the carb rebuilt correctly, gaskets in the correct orientation, metering arm height correct? Has the carb been set correctly, compression...who knows etc etc! Spark plug - seen these give some weird results before, HT lead.....checked for continuity, need I go on!!!

Perhaps one of our members is local and can help, where in the country are you?

[NFG]

Send it to Spud and get it ported as well!

I'd check the common dog stuff like: Air filter, plug colour & the baffle and filter screen isnt gummed up in the exhaust. Then check the oiler is working as a reduction of oil to the bar will slow her up a lot.

My 250 ran best once I'd opened up the holes in the exhaust baffle and put a short bar on it.

Edit: oh er, sounds like its been in bits already...

Edited January 6, 2020 by NFG

[bmp01]

Sounds familiar, is this the same saw with the same low power issue posted about on 21/11/19  ?

 

https://arbtalk.co.uk/forums/topic/118088-stihl-ms-211c-with-low-compression-issue/#comments

 

I think you're going to need someone in the know to have a look at it. You might have more than 1 thing wrong with it which will make it next to impossible to diagnose remotely.

At a push a video of it running and cutting might help. Need to see the saw dust chips too.

 

 

 

[John Rainford]

Thanks for the replies. Yes I am an amateur and learning about 2 stroke engines as i go along. Amazing how many different things can go wrong with such a small engine. I think I will need to take it to a specialist , but I have some time and am going through all the parts carefully to make sure I didn't make an error when I stripped it down previously. So far I have checked the gap on the spark plug, the plug is wet and black, indicative I think of running rich. I have checked the gap between the flywheel magnet and the ignition coil. I have stripped the carb and checked the diaphragms are in the correct places and the right way round. The metering needle is at the correct height according to Zama diagrams and instructions. Used carb cleaner on the carb and checked the strainer wasn't blocked. I have washed and dried the air filter, sharpened the chain, checked the oil flow to the bar, cleaned the carbon deposits from the muffler and exhaust port. I Checked the fuel lines and filter for holes and signs of ware, same with the intake boot. I will remove the cylinder and check the seating of the baring seals, bearings are good. I will check the piston and inside of the cylinder, although from what I can see through the exhaust port they seem fine. I used JB Weld gasket sealer which is good for high temps and fuel resistant. If I don't find any issues after all this I will give up and take it to an expert who will probably diagnose the problem(s) in a few minutes.

[bmp01]

Admire your tenacity mister !

I suspect it's the carb somewhere , from what you are saying about fuel consumption,  black plug etc.

 

Have you checked the second butterfly is opening at anything above closed throttle? As you've had  it apart you'll have spotted the second butterfly/port only supplies air to the cylinder (no fuel). This second port is more than double the area of the small fuel/air port - if it wasn't opening you'd get massively rich engine and little air flow to the cylinder, so no power. I'd guess it would misfire something chronic.

 

Could also be a bad coil with timing gone bad or my current favourite topic - sheared flywheel key giving messed up timing.

Plenty other options...

 

 

 

Edited January 10, 2020 by bmp01
Correction

[John Rainford]

I'll take a look at the second butterfly and check that, thanks.