New member new saw

[Stubby]

2 minutes ago, billpierce said:

Look at an exploded carb diagram for this saw. Check you put back together ok. Gaskets in the right order etc. H and l screw 1 full turn out from fully in.
 

Plus Gaskets the wright way up .............

[pinhead]

Fairly sure it went back as it came apart I laid things out on blue roll so as not to get it wrong it is possible as I am only human 

 

[pinhead]

Strange thing just happened 

I went out and took the carb off again everything was correct and the right way etc so I was desperate to change somehing so I put the old needle back in 

I also tested my fuel filter and line with my vac pump with a pot in line to catch fuel and it flowed fine I was thinking that the aftermarket filter could have been restricted due to poor manufacture

 

Anyhow put it back together and tried it again and it did the same as before but I tried again and just as it was about to die on fast idle it cought again and ran on so it runs I reved it up and down a few times its a little hesitant but I can tune that I think the screws are on 1 and 1 exactly it won't idle but starts straight up again on fast idle 

Thought I better stop as I was in the garage with the door shut and didn't fancy gassing myself and out side would be too noisy this time of night so tomorrow I will try tune it 

[bmp01]

12 hours ago, Stubby said:

Plus Gaskets the wright way up .............

+1 

Having the metering chamber gasket the wrong way up does exactly what you experienced. ...runs on choke, runs on fast idle then dies,  repeat as often you like. 

Don't ask me how i know this. 

If the metering arm height is set too low it could do exactly the same.

 

Just saying .......

 

 

Edited November 24, 2017 by bmp01
....damned auto correct....

[pinhead]

Ah that is probably it then as I put the old arm spring and everything back in 

[bmp01]

So,  how it works. ..

Under choke conditions the choke blocks the inlet track (duh !) which causes a big depression in the carb port AND in the metering chamber (via the tiny jet holes). It's a much stronger depression with choke compared to normal running condition. It's the depression that sucks the metering gasket down onto the metering arm thereby opening the metering valve. Quite simply the bigger the depression the further the valve opens.

 

If you are marginal on opening the metering valve you can see the height of the metering arm or the size of the 'pip' on the gasket are important.

If the metering gasket is up side down. ... there's no 'pip' on gasket, so need big depression to get any movement of the meterIng arm and valve.

 

HTH.

 

 

 

[pinhead]

Well it sort of running right now but I am not impressed 

Got the low speed screw about a turn and a half out and it idle's fine no chain creep with very little on the la screw 

High speed is about bang on 1 turn maybe a 16th more and it does everything it should but it just doesn't excite me it lacks power still just like before really 

We have a ms251 at work so I compared side by side its on the same chain both sharpened by me mine on a 16" 251 on an 18" but only one more link in the chain and doesn't really seem bigger 

The 251 cuts a ring in same price of oak around 10 11 seconds to mine 14 ish I just cant lean on the saw at all it slows down too much and it just doesn'

 Sound crisp 

I am wondering if the metering valve needs a bit more height if not just don't know where to look 

Theory its set a little rich to make it idle and 4 stroke possibly had to do this due to lack of fuel and it doesn't supply enough in the cut 

I did turn the saw off in the cut and looked at the plug it wasn't quite as dark brown as I would like but wasn't grey 

[spudulike]

Here we go again....you need to verify that the cylinder and piston are OEM or at least quality aftermarket. The reason is that the OEM kit will raise around 170psi compression and even high hours machines do this. If the machine has an OEM top end on it then you can get severe skirt wear on high hours machines, usually accompanied with a metallic slapping sound on idle. This would give a lacklustre machine!

 

Lack of power is most likely either a poor top end or a carb that is miles out of adjustment or has issues. The carb should be set to one turn out H&L and if you cant get a decent idle and max revs then you have issues elsewhere. If the saw revs out and idles OK then it is likely the top end is a bit iffy.

 

I have known many Chinese kits make around 140psi and this isn't enough to get decent torque in the cut. It sounds like you are going round in circles. You should always verify that the saw can make good compression, that it has no issues like a nipped/seized piston and once you know the mechanics are good then you can look at the carb and ancillaries.

 

The saws generally cut pretty well and have a fair turn of speed, not a racer but a reliable workhorse! If it is pretty flat then I would be doing the above! Compression isn't the only part as I have seen machines with good compression make no power but a hot compression check usually shows a significant drop in compression.

 

If you don't understand or can't do this then find someone who can!

[pinhead]

I don't have a compression tester and the one I borrowed before the saw went badly down hill was faulty 

The saw now has a farmertech top end yes it is Chinese and this may be the problem but the old top end was genuine the piston is questionable as it has no markings on it 

I will get myself another compression tester and see what it is at now cold and hot 

If I had to guess if the 251 had 3hp as advertised I have about 2.5 not the 3.5 it should have 

I did make a video of the cuts but my phone fell over you can hear the saw well enough though I will see if I can upload it 

[pinhead]

20171124_104601.mp4