Stihl MS260 Over-Fueling??

[hawthornheavyhorses]

My first post on this forum! Hello All!

 

Hoping someone might be able to help on this. My main coppicing saw is a 2006ish MS260 which I have had from new and has been pretty faultless.

 

However last week I was using the saw and it cut out and wouldn't run. I was using it at a bit of a strange angle trying to clean up a cut on some hornbeam coppice. Took it back to the workshop, cleaned the air filter which seemed to have a lot of fuel on, and it ran fine.

 

Next day the saw ran fine for 2 or 3 tanks, and then cut out again whilst the saw was in a similar strange angle.

 

Took it back to workshop again and cleaned airfilter as before but still couldn't get it to run. It would fire cold with choke and run rough for about 10 seconds, but would die and then not restart until cool.

 

So I then did the following:

 

1. New air and fuel filters

2. New properly gapped spark plug. Checked and good strong spark.

3. Took out carb, cleaned with carb cleaner, and replaced the metering and fuel pump gaskets/membranes. Didn't touch needle valves etc.

4. Took off the exhaust and checked the piston. It looks very good, no visible scoring etc. It also feels fine pulling it over by hand, plenty of compression.

5. Fresh tank of fuel from another can (known good)

 

Still no luck, running just as before. So took to local chainsaw specialist and they gave it a brief look and confirmed all the above, and also couldn't start it. They say it looks as though it is overfuelling, and therefore flooding, but would need it in to be looked at properly and they have an 8 week wait!!

 

Relucant to leave it in as I need it so thought I'd try and get it running myself over Christmas, so wondered if anyone had any experience or advice that I could try. I'm thinking it must be carb related.

 

Thanks!

 

Matt

[spudulike]

It sounds like the needle valve may be leaking fuel through a little, very difficult to tell from your description.

 

One problem I have had on the earlier version of the MS260 - the 026 was the spring in the air filter come loose causing the choke flap to open and close at mid to full throttle - it causes a pulsating sound like a very heavy four stroking noise and the saw will run very rich and not rev well.

 

Fire the saw up with the orange air filter cover removed and see if the choke actuator on the bottom right hand side of the airfilter is flipping open and closed whilst the saw is running.

 

Also check the breather - possible it had dust in it and now a bit of fuel that has totally clogged it and is causing fuel starvation.

 

What colour was the plug - black, white or tan?

 

If you get stuck, PM me - I may be able to sort it out while you wait the week after Christmas

[hawthornheavyhorses]

Thanks for that. Original Spark Plug looked fairly good, a tan colour I would say.

 

The new one hasn't had a chance to get a colour as yet, but is definately getting fuel.

 

I've changed the airfilter for a new one, and no change, so suspect that's not the culprit, but will double check tomorrow.

 

I also tried running the saw with the breather partially off to rule that out, again no change.

 

I got a needle valve with the carb kit, so will try changing that over. Any tips on setting the hight?

[felixthelogchopper]

Can recommend Dave Harris in Rayleigh who works a few days a week for Stantons.

[spudulike]

Thanks for that. Original Spark Plug looked fairly good, a tan colour I would say.

 

The new one hasn't had a chance to get a colour as yet, but is definately getting fuel.

 

I've changed the airfilter for a new one, and no change, so suspect that's not the culprit, but will double check tomorrow.

 

I also tried running the saw with the breather partially off to rule that out, again no change.

 

I got a needle valve with the carb kit, so will try changing that over. Any tips on setting the hight?

 

If you are using the original metering arm then the height won't need adjustment but it is a Zamma carb so between 0.3mm below to level with the carb body - just lay a flat edge across the carb body.

 

Can't be too much wrong with it - nobody has been messing with the H screw have they?

 

Just had a thought - take the diaphragm cover off and make sure there isn't a load of sawdust under the cover - that may cause the diaphragm to be pushed up and letting too much fuel in!

[GardenKit]

Just one more idea. I had one with similar symptons, i.e playing up on an angle. It turned out to be a very small split in the fuel pickup hose which normally stayed closed, but the AV,s were also knackered and when the handle was pulled away from the tank at a certain angle it opened up the split.

This starved the saw, but when the engine stopped the fuel ran out of the split and poured over the air filter until the saw was righted.

May be worth a look?

[hawthornheavyhorses]

No messing with the H screw before the problems started (in fact I've never needed to adjust them). I checked the screw settings after, the H screw actually has a limiter on so it can only turn 3/4 of a turn anyway!

 

It's actually a Walbro WT carb fitted to mine, not sure if that makes a difference?

 

Cleaned under the diaphragm cover when I took the carb out, nice and clean.

 

I'll double check the fuel line tomorrow, does sound as though it could be similar.

[spudulike]

No messing with the H screw before the problems started (in fact I've never needed to adjust them). I checked the screw settings after, the H screw actually has a limiter on so it can only turn 3/4 of a turn anyway!

 

It's actually a Walbro WT carb fitted to mine, not sure if that makes a difference?

 

Cleaned under the diaphragm cover when I took the carb out, nice and clean.

 

I'll double check the fuel line tomorrow, does sound as though it could be similar.

 

Yes - Walbro carb - there should be a raised moulding around the arm - the arm should be level with this - alternatively, there is a setting gauge tool you can buy.

Edited December 20, 2011 by spudulike

[hawthornheavyhorses]

Thanks Spud, didn't get to look at it today, hopefully tomorrow. If in doubt I may be popping over to see you! Will let you know how I get on.

[agg221]

Can recommend Dave Harris in Rayleigh who works a few days a week for Stantons.

 

Sorry to derail, but is that the same Dave Harris who works for Essex Wildlife Trust?

 

Alec