Ms261 problems

[Allweathers]

Right guys and girls...I have an old 261 C 2013. Bought secondhand as a project...Replaced crankshaft, bearings and seals...new piston and rings using saved original head. Top end replaced due to recent seizure. This was probably due to fuel and or running too lean...coil fine, spark fine however before It seized I could tune it to run but when it got hot it wouldn’t start...!!! Then it seized...Now I was a mechanic so would like to think I have some knowledge although this is now pissing me off!!!...and I have spent hours trying to get this saw to run but since I replaced top end I can’t get it to run...start stop cables all inspected and fine..new tank breather recently fitted and copy carb cleaned although this is pretty new..took head off no broken rings..used a ring compressor. Pressure tested and vacuum all hold. I have even heated it with heat gun around crank etc under vacumn and pressure to simulate it at hot and both hold!!! What on earth is wrong!!! I can get it to start on choke and keep it running flicking between full choke and half choke but it’s revving like hell then just bogs...only thing I haven’t replaced is fuel pipe and filter. Filter looks fine but pipe may be getting a bit sloppy...is it getting sucked flat??? I’m at the end of my tether...no spark arrester cos over the pond!!! Please give me some suggestions!! Excellent compression...is it the cheap carb??!!! PLEASE HELP. 

[Wonky]

Sounds like it’s still lean or there’s little compression, so it sounds like the carb.. Those cheap carbs can be a bit a bit tedious to set right

the best way to find Out if the carb is faulty, is to pull a good one off another saw..

I know we all don’t have another saw thou..?
 

Also adding, if you suspect fuel line or fuel filter you could find a way to just bodge another line in a cup\small bottle  with fuel. But it’s unlikely it’s the fuel line going flat straight away. But only if the filter is bad. 

Edited July 12, 2020 by Wonky
Adding

[Allweathers]

Thanks wonky...ok so the update is this...leaking decompression valve found as a result of compression test. Tiny air bubble through the soapy water so obviously not closing properly... now replaced with blank.I think this may have caused a sticky ring initially which may have caused the issue with hot starts. May have made it run lean and caused the eventual seizure!!?? The carb was working fine before the top end change and although I have used nearly a can of carb cleaner on it from close inspection it looks like there are minute shiny pieces of aluminium. Maybe one of the ports is blocked??? I’m going to strip it out again and blow it out!! It may of course been the filter causing lack of fuel so I will replace that too!! I just want it to run mate!!!

[Khriss]

I would swap over a cheap Chinese carb - see if symptoms change . Probly 10 squid off eBay.   Would renew yr pipes regardless.  K

[Allweathers]

Frammo...thanks..I am determined to get to the bottom of it...cylinder not bad just some aluminium deposits which I removed then went over with wet and dry. I bought another non oem pot but have not used that yet. I went for a half decent one rather than dirt cheap one!!

 

 Khriss...yes definitely getting new pipes..will try and clean existing carb as worked fine before seizure and give it one more go...you see it runs on choke so it’s very lean but I don’t know where it’s getting all this air from. Vacumn and pressure test fine!!! ????

[Stubby]

1 minute ago, Allweathers said:

Frammo...thanks..I am determined to get to the bottom of it...cylinder not bad just some aluminium deposits which I removed then went over with wet and dry. I bought another non oem pot but have not used that yet. I went for a half decent one rather than dirt cheap one!!

 

 Khriss...yes definitely getting new pipes..will try and clean existing carb as worked fine before seizure and give it one more go...you see it runs on choke so it’s very lean but I don’t know where it’s getting all this air from. Vacumn and pressure test fine!!! ????

Could just be a split fuel line .

[Allweathers]

Stubby checking that this arvo...will get back!!

[Allweathers]

Will do...will keep you all posted..thanks       ..to all?

[Allweathers]

Right got the bloody thing started with the cheap carb after dropping it in carb cleaner for a couple of hours and blowing out. Cannot tune it both screws h and l are sitting about three turns out. It idled for about 5 minutes and revved with no bogging but I can’t get it 2 stroking so am in the market for a genuine carb if anyone knows where I can get one. I may have to go over the pond but it will cost!!! Running it on 40.1 mix with premium fuel 97 octane. Is that ok or should I go for a tub of aspen? 
 

well I hope it is the carb but I’m in a better spot than I was 2 days ago...can’t understand why it’s gone from a tune-able carb to absolute crap. Unless it got a gob full of aluminium when it sized or the heat has got to it. Any ideas????

[Allweathers]

Normal searches on eBay gumtree etc...this bloke is always breaking saws and selling stuff but do I drop £40 quid on a maybe gamble?? I guess all the L screws are replaced after limiter removed to get them running richer...is that correct??