STihl 075AV Tillotson Carb Tuning Assistance

[1_badger]

Hi,
I've been attempting to restore, for the past 2 years, an old 075AV I bought from France via Ebay (I'm based in the UK). I've finally got the saw running but I now need some guidance / advice on tuning the tillotson carb. Having rebuilt the carb I set the H and L screws as outlined in the service manual at 1 and 1.25 turns out. With the choke open the saw starts fine and throttles up okay perhaps idling slightly too high, but as soon as I close off the choke she dies. I'm new to this so I wondered if the idle screw needs adjusting. Whilst the manual mentions the idle screw there's very little information on it other than its set at an optimal setting in the factory and you might have to adjust it if you're working high above sea level. Does anyone know if there's a "standard" setting for the carb idle screw for working near sea level. I'd like to adjust it to tick over steadily once its warmed with the choke closed. Having looked at a number of other threads I've not discounted issues with seals and other problems which I haven't looked into yet, but if anyone knows any basic carb set up guidance particularly with respect to the idle screw I'd be grateful.

Cheers,
Nick Foster

 

[president]

Hi,
I've been attempting to restore, for the past 2 years, an old 075AV I bought from France via Ebay (I'm based in the UK). I've finally got the saw running but I now need some guidance / advice on tuning the tillotson carb. Having rebuilt the carb I set the H and L screws as outlined in the service manual at 1 and 1.25 turns out. With the choke open the saw starts fine and throttles up okay perhaps idling slightly too high, but as soon as I close off the choke she dies. I'm new to this so I wondered if the idle screw needs adjusting. Whilst the manual mentions the idle screw there's very little information on it other than its set at an optimal setting in the factory and you might have to adjust it if you're working high above sea level. Does anyone know if there's a "standard" setting for the carb idle screw for working near sea level. I'd like to adjust it to tick over steadily once its warmed with the choke closed. Having looked at a number of other threads I've not discounted issues with seals and other problems which I haven't looked into yet, but if anyone knows any basic carb set up guidance particularly with respect to the idle screw I'd be grateful.

Cheers,
Nick Foster

A nick( canadian hello ) whilst peering down at carb(air filter off)look at where the throttle lever at carb end
you;ll se the mechanical idle screw protruding thru the carb body and its usually 1 to 1and a half turns in after it
contacts the throttle lever plate for initial adjustement cheers

 

[harrygrey382]

If it's idling high with the choke on you have an air leak somewhere. There are many possibles on this saw... around the 1 turn mark out is standard (1.25 sounds right even). You could back the L out to 2 turns and see, but even if that makes it run ok it's still richer than it should be (so compensating for more air from somewhere).

Quickest way to find the leak is to pressure/vac test the saw. Or you could inspect all seals/gaskets (carb/intake gaskets, crank seals including oiler seals, impulse line). Check the fuel line for a small hole as well

 

[1_badger]

Harry and President, just wanted to say thank you for the inputs. I'm hoping to get the case pressure tested once I can track down a pressure kit. Will update on progress when I make some. Cheers Nick

 

[1_badger]

Have to add, even though it's an AV model I can't rule out that one of my flange joints hasn't shaken loose, it doesn't half vibrate at high revs, I'm going to get some threadlock to secure the screws better - Nick