Cleaning carb on smoking Stihl

[coppicer]

Hooray! Sort of. I gave it some fuel and oil. The saw fires as normal on choke, I flip it to normal, then it catches, runs for a second or two, then dies. Sometimes I can get it to rev for a few seconds. I'm assuming that this is a carburation issue? I dialled the three carb screws all the way in and out to what I thought was default, but maybe I got it wrong.

 

Second issue: ring-a-ding-ding from the washer on the end of the crank stub in the picture below. It's held on by an e-clip, and there seems to be a lot of play, so it tinkles on over-run. I can't seem to find a close-up picture in the documentation as to which side should face out, so I'm thinking that maybe I have it the wrong way.

 

Can anybody advise on either of these? Thanks.

 

[bmp01]

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.

[coppicer]

Thanks, not had any luck with that so far, but I will try resetting all the screws. I replaced the pump diaphragm a few days ago and I don't think it's possible to put it back together incorrectly if you're following the manual, but maybe I did something wrong.

 

On the positive side, bar oil is flowing through the saw, which is good - I was concerned that the oilways were blocked.

[woodwizzard]

You say three screws. Don't forget one of those is the tick over screw, so won't have a factory setting as such. You will probably need to be screwing that in a bit to get it to keep running.

[coppicer]

1 minute ago, woodwizzard said:

You will probably need to be screwing that in a bit to get it to keep running.

Er, I've been unscrewing it further! Is that the wrong direction?

[bmp01]

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.

 

Edited August 2, 2020 by bmp01
Filter note added.

[coppicer]

2 hours ago, bmp01 said:

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.

Didn't check any of these! Thanks, will get onto it.

[spudulike]

I would set the metering arm if not done already and then hold the carb up to the light, open the choke and turn in the idle screw until you see a very small amount of light around the brass throttle valve plate. 

The carb should be pretty close to going then. The other suggestions are a bit more complex and would be a phase two if the saw still didn't function like this.

It is always worth doing the obvious and easy things first and then progressing to the more difficult if the easy stuff fails.

[coppicer]

4 hours ago, spudulike said:

I would set the metering arm if not done already and then hold the carb up to the light, open the choke and turn in the idle screw until you see a very small amount of light around the brass throttle valve plate.

I'm all for doing the easy things first (and exclusively, if possible). Anyway, now been waylaid by wife to begin assembly of IKEA item. Looks possibly more complex than the carb.

 

EDIT Furniture is supposed to have 20 screws, M4 x 10mm. There are only 19 in the bag...

Edited August 2, 2020 by coppicer

[coppicer]

Sorry about this @bmp01 and @spudulike, but with regard to your comments, I'm using the Stihl repair manual and it doesn't mention a metering arm anywhere (only a metering diaphragm). Is it the "air valve lever" referred to in the screenshot below?