MS181 spluttering and bogging down at high revs

[Ratman]

Thanks [emoji106] will keep playing, seen where it is through body... sneaky little sod! Might just do as you said then if its working ok for you up to now, just retune as normal then using tacho or any minor tweaks to be adhered to?

[bmp01]

Accelerator circuit is for response during. ... wait for it. .... acceleration (ie increasing engine speed). In the steady state of wide open throttle it does nothing. You can understand this when you've seen the bits in front of you - the piston doesn't move any further once the throttle shaft has reached wide open throttle. ... 

 

So all you are trying to over come once the accelerator circuit is disabled is that initial stumble when you quickly open the throttle. I set the saw up a little rich on the low speed circuit. So at idle, find the fastest engine speed with the low speed screw, then back it out until idle speed drops slightly. Blip throttle , check for response...

Worth noting, at operating speeds the low speed circuit is responsible for 25% ish of total fuel to the engine. So there might be a requirement for a small tweak to the high speed circuit.  (That 25% number came from Zama website, sounds very approximate to me, but the principle holds).

 

But let's not get too far ahead. Check the condition of the accel piston first. 

 

 

 

 

[Ratman]

Tidy [emoji106]

[Ratman]

Had the carb apart to check the throttle accelerator valve as suggested, all looks good but obviously it isn’t to say that it could be worn. Did take pics of everything at stages but my phones life expired and i’ve lost a lot of photo’s with info etc on them, gutted [emoji30][emoji24]
So rebuilt everything and put some fresh fuel in, 6 pulls on choke and got the plutter, flick to half choke she fired, flick throttle and she idle’s sweet [emoji108] press trigger and its no different, sometimes it will rev out great sometimes it will start to bog then revs out fine, sometimes it will rev out fine but bog and splutter at top end!!! [emoji37][emoji35] driving me mad! I’m contemplating buying a cheap carb as a test carb for future, for the amount of use it’ll get from me for test purposes its never going to get worn out anytime soon, and if it shows a resolve then my bod can decide whether he wants to fit a cheapie or buy a genuine expensive one. Unless anyone else has any ides? [emoji6]

[Ratman]

Have tried two more new spark plugs just to rule them out, ngk and bosch to eliminate any brand differences if there are any and if they affect the saw in any way.
Reset L and H back to factory, have had a very slight difference in performance by just altering an 1/8th of a turn anti on the L. Knocked idle screw an 1/8th anti too, pretty good clean response most of the time but will occasionally try and bog from initial press, and so on and so on as above thread states.

[billpierce]

Are you familiar with tuning saws? It may need further carb adjustment.

The farmertec carbs on eBay aren't too bad. Certainly ok for a year, but you need to be able to tune them

[lurkalot]

A good strip and sonic clean and a new set of diaphragms normally cures them for me.  Talking of Diaphragms, what condition are they in?  Although the metering Diaphragm might look ok, if it's gone stiff at all it'll affect the running.

[Ratman]

Are you familiar with tuning saws? It may need further carb adjustment.

The farmertec carbs on eBay aren't too bad. Certainly ok for a year, but you need to be able to tune them

Hey Bill, messed around a little with em but not masses, can generally get em near as damn it. This is one pig tho!!! I’ve ordered a cheapy carb off flea bay, will see how she runs when that goes on.

[Ratman]

A good strip and sonic clean and a new set of diaphragms normally cures them for me.  Talking of Diaphragms, what condition are they in?  Although the metering Diaphragm might look ok, if it's gone stiff at all it'll affect the running.

Hey lurkalot, its had a full carb kit plus diaphragms / gaskets etc, as above tho i’ve just ordered a cheapy carb off the bay, will keep you all updated with the outcomes [emoji106]

[spandit]

My MS181 dies when I press the trigger. Think I'll order a new carb too