bmp01

9 hours ago, coppicer said:

This one feels like plastic, not rubber (or metal). Will have a poke around.

.... plastic not metal.... fair enough. Its just to stop the rubber manifold from collapsing in under closed throttIe vacuum.

No12 is a metal ring that plugs into the rubber manifold. I think its no 5 - which seals the reference pressure on the metering diaphragm to the pressure in the air box. Otherwise it would be referenced to atmosphere, (how older saws are). Its a simple dodge, to try to correct fueling when the air filter is partly blocked. Cant see it making much difference at idle, clean filter situation.

So, fuel in the pump but not the metering side eh ? Obviously you did get fuel in metering side (on choke) or it wouldn't have run at all. Then again saws been stood for a few days so maybe evaporated off, not conclusive.

Added a bit more to that post as an edit....

Metering arm lives under the metering diaphragm, requires the carb to be pulled apart...

IIRC its a Zama carb on these, the Zama website is quite helpful if you can tolerate some reading and pondering.  There's a full explanation of how the carb works on choke, part throttle and open throttle plus the pump and metering arm layout. ...

Head to http://www.zamacorp.com/ then look for SUPPORT, then TECHNICAL SUPPORT then DISSASEMBLY AND SERVICING (types C1U etc).

Down the page you'll see this:

It used to be you could download this technical guide, not sure that's possible now. 

Anyway,  that's the metering arm stuff,  you need to decide if it's the type A or B, can't remember.

Whie you're in there, there's the filter to attend to. 

Pretty sure you can check the main jet one way valve in situe by accessing one or t'other drilling while closing high speed screw.....

Unscrewing the idle screw too far out will disable the idle circuit but you'd have to go a long way. If engine starts like this it will rev high - like the high idle position on choke switch. 

The pump in the carb is pretty straight forward, as you say if the diaphragm material is in good condition, correctly positioned against the carb, gasket against cover, then probably ok. You need the crankcase pulse signal to reach the carb but there's no separate impulse line on these, its combined in the rubber boot, worth checking for splits though.

A few other things, 

-did you check and set the meter arm height in the metering side of the carb ? Maybe fuel is getting to pump but going no further, coz the metering valve is closed. Research on here, been covered many times. If you strip the carb after the engine stops (no choke) pay special attention to where you find (or dont find) fuel, it can help with diagnosis.

-did the filter in the carb get changed ? Same logic as above.

-main jet one way valve not doing is job,  happens if an air line has been used to clean main jet. Check by bIowing each way through the jet with a piece of soft tube. 

-accerator piston and its oring worn out, needs removing and inspecting, happens on old or high mileage saws. Also been covered on here.

Second issue - doesn't sound like an issue.  Once you have a bar/chain on there,  sprocket will slow down much quicker. Side cover will reduce sounds too.

First issue,  yes carb. 

Starting on choke sucks fuel into the carb.

The brief running off choke is using up the fuel that's now in the carb/engine.

Either the mixture is a bit Iean - so as the excess fuel is used up the carb is not supplying enough fuel.

Or the fuel pump in the carb isnt working, so the carb (and engine run out of fuel). Off choke the carb cant suck fuel up, so you need the pump...

First punt, back the low speed screw out an eigth turn, try it.  ...then try another eigth turn and try it.

If no improvement your probably into pump issues.

17 minutes ago, spudulike said:

And stick your tongue on it to test it

Not sure if I'd want it to be working or broken at that stage, emoji is spot on.

32 minutes ago, kevinjohnsonmbe said:

Obesity is a classic example of what I’m interpreting from what (I think) you’re saying....

Nope not what I meant .... although obesity seems another thing were not good at (or good at depending on your persective).

In a nut shell, I meant we (in the uk) dont like to be told what to do, we dont like following rules or guidance (compared to other nations). 

Read a few pages of this .....

Seems to me there might be a correlation between the attributes of the free minded UK population and how well the UK is doing in this pandemic.

Absolutely no point blaming anyone in authority (government or medical establishment) for not steering the ship in the right direction because 'we' pay no attention to it anyway. I'm not referring to individuals on here necessarily - but you can see it everywhere in society from the groups of teenagers 'behind the bike sheds' to the parents at the school leavers parties, the callers on the Jeremy Vine BBC radio 2, the beach invaders etc, etc,

On this particular challenge it seems our society is not best placed to achieve a great result. Individuals dont have a unified goal or the will power to weather the isolation (or what ever the requiement is) and crucially we dont have the dractonian penalties of the communist counties where the control of people becomes easier.

We're just set up different, good for some things not so good for this.

Interesting reading that Macpherson. I like the logic, worth a punt for me. 

I like that there is no product for sale (ie no financial angle), although I guess we shouldnt discount the author making a name for himself and maybe he has an axe to grind with established pharmaceutical companies.

Turmeric (pills) is a natural alternative to conventional anti inflammatorys. Not saying its a replacement for stong pain killers as seems less potent, but has its place and helped me through sciatica and minor disk operation. 

From my limited experience I'd say that's reasonably conservative cylinder pressure.   Looks like you've gone for a small squish to get over the high exhaust port ( "97 degs ex" ---> 166 exhaust duration, big number). You dont get any piston to det band contact with that ? 

6 hours ago, frammo said:

personally i only compression test ported saws to check i havent overdone it..

Ok. Interesting point, what numbers do you use to say you've over done it? 

220psi is ok for a works saw but I've not managed that. ..

Post deleted

Flexhones are pretty harsh and not what you'd call precision items. Seen them used on 4 stroke engines successfully after some practice but don't think I'd like them 'balls on sticks' running across a port. At least with the brake hone the stones are tall enough to not 'fall' into the port.

Just my 2 pence worth....

On 08/07/2020 at 16:05, Stubby said:

They look like Belleville  Washers in the stack . I suspect you compress the washer stack to enable a circlip or wire retainer of some sort to be removed . Probably a dedicated tool for it .

This.

If you've got the clip off already (top pic shows it still in place...) then yeah if might just be crudded up. 

Presumably you've composed the belleville washes so they ought to have loosened off.... should slide off....

Nice one.  Thanks for the update.

Plenty of 'how to's' on carb tuning on here and on t'internet.....

Smokey, might be if previous owner was trying to tune out an air leak ( ----> lean mixture)....but don't bank on it, make sure fueling is right or it'll seize again.

40 minutes ago, Liam Outdoors 89 said:

 

Day 3 issues started....

 

Really high idle, adjustment slows it down then creeps up again. Saw just starts ragging it's arse off for no-reason.

 

So either the idle screw is winding itself in (while you are running the saw away from idle) or you've got an air leak so the throttle can't restrict the amount or air / fuel into the engine. The latter will cause engine to seize if not attended to. 

54 minutes ago, spudulike said:

......and I know where the local tip is

Nah, you haven't got the patience to wait in a 2 hour long queue......

Had similar question a week ago,  see here. ...

https://arbtalk.co.uk/forums/topic/120859-after-market-seal-kits-carb-rebuild-kits-any-good/

"that’s a Stihl “in house” spec bearing"

Hate it when they do that. ...  But fair enough, you've not much option and as you say if you're doing one then might  well be consistent and do the pair.  

"Bearings I’ll stick with OEM, no doubt in them then"

...that's the one place I'd go "aftermarket" if theres a saving, you can often see FAG or INA etc on the OEM part. Buy the same or another top brand part from a bearing stockist...

-get the right running clearance,  press fit brs are often c3 grade. 

-don't buy no brand Chinese bearings for chainsaw, ever.

-check cage material, piston pin needle brg must be metal cage, clutch brg advisable in metal too. 

The expression 'hit and miss' is about as conclusive as I can get with aftermarket stuff.

Pistons are better quantifed, Meteor are good, Hyway ok, Vtec and Golf last resort in my experience. But some peeps have fitted no brand pistons and got away with it - maybe long enough to flog the saw.

Bearings - establish what you need and source known brand stuff,  that's a good saving over OEM while

keeping quality.

Consider what saving are you making in relation to consequencd of part failing. If it's buried in the engine it'll be a full rebuild at best eg piston circlip. Side screw at 10p vs 2 quid then why not.

Aye, all true.

How long to diagnose? I'd guess at under 5 minutes for this one.   

Chap who did my MOT's insisted on driving car into the test station,  said he could tell in the space of 25 meters whether he had to spend time on a car. And before that he had a good feel just from sauntering up to the car, critical eye plus experience....

16 hours ago, Shepherdess said:

I can assure you, all that has been tried but thanks. 

 

I don't doubt its all been tried.  What is surprising and a little disappointing is the lack of detail.

For instance,  if the muffler was removed (as suggested) its the work of a few minutes to upload a picture. Ye'know cant even be bothered to confirm if the spark plug was soggy wet or bone dry ?

But anyway no point wasting breathe.  Bye  ? .

24 minutes ago, Shepherdess said:

I should state that my husband is not an inexperienced idiot! He had worked with various machines and engines all his life and can usually solve most problems himself ....

Good to hear, the chainsaw and idiot relationship is not necessarily an enduring one

In fairness that 'idiot' comment was directed at those offering advice (to work on the saw), not your husband. 

Good luck, some feedback might help in due course - it's impossible to say with certainty what the problem is at the minute.