Tuning carbs with no L and H screws

[billpierce]

will have a check, but reckon they are alright, you can hear that its idle is high!

[bmp01]

I agree saw looks like it is running rich, probably rich at idle too.

I bet it is leaning out - that's to say getting closer to optimum - when hanging on the strop, so the idle speed goes up.

I wonder if in that orientation - the fuel line is pulling a mixture of fuel and air ie fuel pick up isn't fully dipped in the fuel. ..maybe the fuel level in tank is on the low side?

 

bmp01

[billpierce]

fecked around with this saw again, fuel lines look good, no pinching or splits, cuts and revs fine but either chain creep (fast spin) when saw is level or if backed off til no chain creep, saw dies when hanging on strop.

 

full of fuel. real puzzle. you can alter the revs bypushing/twisting the trigger handle, but i think this is just the carb lever getting pulled slightly.

 

no other ideas? or clues?

 

thanks

[bmp01]

fecked around with this saw again, fuel lines look good, no pinching or splits, cuts and revs fine but either chain creep (fast spin) when saw is level or if backed off til no chain creep, saw dies when hanging on strop.

 

full of fuel. real puzzle. you can alter the revs bypushing/twisting the trigger handle, but i think this is just the carb lever getting pulled slightly.

 

no other ideas? or clues?

 

thanks

 

So, obviously you've checked the throttle linkage isn't tight sitting level...

 

 

Back to the idea that it's fuel related, seems i had it arse about face in my previous post, so does it immediately idle slower when hung up or does it progressively get slower and finally stall? If it were rich at idle (I'm assuming it might well be from that plug) and then made richer it would get slower (and possibly slower and slower until it stalls).

 

What's the orientation of the carb? I'm wondering if the metering lever and valve are working (but only just) when the saw is level, and not operating when the saw is hung (i know the spring on the metering lever ought to cope with this but if the valves not sealing, who knows).

Solution in this case would be: check the valve, set the metering lever correctly, make sure the metering diaphragm is up the right way and also that the gasket is between the carb and the diaphragm etc. If that's good you could try squashing the metering lever down a 1/4 mm in the name of experimentation ...

 

 

Also is the metering chamber vented to atmosphere or is there a compensation for filter blocking?

 

bmp01

[billpierce]

So, obviously you've checked the throttle linkage isn't tight sitting level...

 

 

Back to the idea that it's fuel related, seems i had it arse about face in my previous post, so does it immediately idle slower when hung up or does it progressively get slower and finally stall? If it were rich at idle (I'm assuming it might well be from that plug) and then made richer it would get slower (and possibly slower and slower until it stalls).

 

What's the orientation of the carb? I'm wondering if the metering lever and valve are working (but only just) when the saw is level, and not operating when the saw is hung (i know the spring on the metering lever ought to cope with this but if the valves not sealing, who knows).

Solution in this case would be: check the valve, set the metering lever correctly, make sure the metering diaphragm is up the right way and also that the gasket is between the carb and the diaphragm etc. If that's good you could try squashing the metering lever down a 1/4 mm in the name of experimentation ...

 

 

Also is the metering chamber vented to atmosphere or is there a compensation for filter blocking?

 

bmp01

Cheers, will check all of that carb stuff this weekend. Appreciate the help

 

Bill

 

Sent from my C6603 using Arbtalk mobile app

[neiln]

choke sticking slightly closed? would cause it to run rich, fast idle but slowly coke up at idle making it stall after a while. Is the strop thing a bit of a mislead, orientation not the problem, just that it doesn't normally idle long enough at other times to coke up.

[billpierce]

Well you'll all be pleased to know that the carb boot had split. Causing an erratic idle and revs changing when held at a different angle. Haha!

[billpierce]

[peatff]

What's caused that, is it rubbing or is something pulling on it and are spares easily available ? Good to find and fix a problem though. I had a moped with similar problem but it only used to stop when it rained. I just wrapped amalgamating tape round the manifold and it ran for years like that.

Edited September 5, 2017 by peatff

[billpierce]

What's caused that, is it rubbing or is something pulling on it and are spares easily available ? Good to find and fix a problem though. I had a moped with similar problem but it only used to stop when it rained. I just wrapped amalgamating tape round the manifold and it ran for years like that.

If I had to get it'll be me pinching the saw up a tree and yanking it to try and sort it. Will be more careful.

The boot cost about £2.80 so I bought 2. Very surprisingly cheap. Running like a champ now.

I would drill the exhaust but..... No l and h adjust!

Sent from my SM-G390F using Arbtalk mobile app