Stihl MS231 starting problem

[aidank]

A few mths back I had starting problems with a Stihl MS231. 2018 saw, not a lot of work done.

 

Its supposed to start as follows.  

 

• Close Choke and pull a max of 3 times.  Within these 3 times it should jump to life and run briefly, ~0.5secs.  (If you dont get it to do this brief run it will not start, regardless of how many times you pull or choke position)
• After the 0.5sec run as mentioned above open Choke and pull again.  It should fire up within 3 pulls. it pretty much always does.

 

When it was running correctly it would perform as above. 

 

Over time a problem developed that it would not run briefly with the choke closed, and eventually it would get flooded from pulling it, and spark plug would get wet.  

Spark plug would then have to be removed and dryed and chainsaw pulled a few times with plug removed to clear out the flooding from the cylinder.

Problem got worse over time and if saw was left idle for even a day it would flood itself.  Fuel appeared to be making its way from fuel tank into the cylinder and wetting the spark plug first pull.   

 

Dropped it to the local shop and replaced all filters and spark plug, no better.  Back to shop again and replaced seals in carburettor.  - All was now good, and it ran fine for few weeks.  idles are all perfect v well tuned actually.

 

I filled petrol tank in yard on Saturday and started without issue - was actually thinking to myself seal replacement was a great job.  I left it run for a min and switched off.   I then had to walk 1 mile carrying saw with a full tank of petrol, 20min walk, as you can imagine saw is tossed about from me carrying it.  Tried to start and found saw was flooded and would not start at the end of my 20min trek, and required spark plug to be removed and dryed.

 

Same again on Sunday morning........

 

I guess im wondering is it normal that the shaking and tossing about during my 20min walk could allow petrol into the chamber, or is there something still wrong in the carburettor.  its probably time for entire new carburettor is it ?

 

Its a Zama Carburettor

[aidank]

I guess I was wondering should it make any difference which position the choke position is in during my 20minute trek

[Muddy42]

The fact the fuel ends up being shaken into the cylinder isn't right.  If you apply air (gently, 3 psi is more than enough, too much can cause damage) to where the fuel line enters the carb it should hold pressure and not let in any air and hence fuel. 

 

If it leaks hold the carb under water to trace the leak - maybe one of the covers ins't screwed down properly.  It could be that the valves (that are part of the diaphrams that the shop replaced) are leaking, installed badly or the needle is not closing properly or the spring is weak. The repair place should have checked that the carb was working after installing a carb kit.  Find someone decent.

 

Generally chokes enrich the mixture by restricting air not adding more fuel so the position of the choke shouldn't matter.

[GarethM]

I wouldn't say it's leaking, more the choke is just letting too much build up in the cylinder.

 

Messing up the ratio to the point where it'll never ignite, had to remove the plug once or twice on an ancient Ms250 years ago.

 

I tended to pull it over normally once or twice, if it fired happy days before resorting to choke.

 

Weirdly on my 251, I tend to rev and hit the stop button helps on the next restart.

Edited February 21 by GarethM

[spudulike]

From your description of the issue, it sounds like the carb needle valve isn't set right or it is leaking. The needle valve in the carb, stops the fuel from the tank ending up flowing straight through the carb in to the engine hence my thinking the valve isn't sealing correctly. 

It is possible that there are other issues but a saw shouldn't flood just through carrying it for a while....it is possible if the saw is left out in full summer sun and the fuel expands but it isn't that common.

[aidank]

18 hours ago, Muddy42 said:

The fact the fuel ends up being shaken into the cylinder isn't right.  If you apply air (gently, 3 psi is more than enough, too much can cause damage) to where the fuel line enters the carb it should hold pressure and not let in any air and hence fuel. 

 

If it leaks hold the carb under water to trace the leak - maybe one of the covers ins't screwed down properly.  It could be that the valves (that are part of the diaphrams that the shop replaced) are leaking, installed badly or the needle is not closing properly or the spring is weak. The repair place should have checked that the carb was working after installing a carb kit.  Find someone decent.

 

Generally chokes enrich the mixture by restricting air not adding more fuel so the position of the choke shouldn't matter.

 

 

3 psi - was i to remove carb and blow into it via a bit of tube would my lungs nearly produce adequate pressure for that ?  

 

[aidank]

18 hours ago, GarethM said:

I wouldn't say it's leaking, more the choke is just letting too much build up in the cylinder.

 

Messing up the ratio to the point where it'll never ignite, had to remove the plug once or twice on an ancient Ms250 years ago.

 

I tended to pull it over normally once or twice, if it fired happy days before resorting to choke.

 

Weirdly on my 251, I tend to rev and hit the stop button helps on the next restart.

 

 

what would i need to do to correct the choke issue

 

[Muddy42]

2 hours ago, aidank said:

 

 

3 psi - was i to remove carb and blow into it via a bit of tube would my lungs nearly produce adequate pressure for that ?  

 

Yes I often do this!

[GarethM]

2 hours ago, aidank said:

what would i need to do to correct the choke issue

I just find them a bit crap at starting, that's why I pull over on run first and not choke.

 

On my occasional use, 261 being the main workhorse. Holding the throttle whilst not best practice usually start then.