Husqvarna 36 won't run

[flatyre]

just bought this little saw for £20 complete with brand new chain. It had been shelved a year ago after failing to start, I blew out the filter, fitted a new plug and some fresh petrol and it fired up after a few pulls. However as soon as I knock the choke off it revs up without pressing the trigger then dies, pull the choke out and give it a pull and it starts again until the choke is knocked off, revs up again without the trigger being pulled then dies. Any ideas whats wrong with it and is it worth fixing and keeping as a back up saw?

 

 

[Stubby]

Its got an air leak from somewhere . Or fuel starvation . Or both .....Check the small round gauze filter in the carb . Check all the rubber components for splits letting air in . Also check the tank breathe is not blocked .

Edited November 9, 2015 by Stubby

[adw]

Fuel starvation, start by replacing the fuel filter in the tank, no better, carb off, check the internal screen under the pump cover for dirt, replace diaphrams if hardened, behind the carb fixing plate you will find the rummer induction tube, check for splits, uner the induction tube is the impulse tube seal, make sure this is in good condition, failing all this check the crank seal behind the flywheel, they are prone to blow inside out.

[spudulike]

Probably fuel starvation, check the fuel line, filter, carb gauze strainer and give the carb a good clean. Pull the H&L screws and get some cleaner down them.

 

Most saws that have not run for a long time and fail like this are fuel issues some may develop air leaks.

 

The fact the saw will run on choke means the high speed carb circuit is working but the low speed one could be blocked or there is a lack of fuel at idle.

[flatyre]

Thanks for the advice guys, I took the carb off and stripped it down, no obvious gunge but I did find something when checking the rubber carb manifold. Below to the left of the oval carb port is a smaller circular port about 8mm. A small pipe runs through the carb backing plate and into this smaller port. There is a little rubber grommet forming a seal between the port and pipe which is starting to break down. I've never noticed it on any of my Stihl saws, is it some sort of breather? and could this be causing the problem? Also the carb was fairly clean and the fuel line looks ok, but the rubber seal on the fuel filler cap isn't doing its job, could this be contributing or irrelevant? Again thanks for the advice so far.

 

 

 

[spudulike]

That is what we call the "Impulse Line" as it takes the positive and negative pressure from the crankase and allows the carb to use it to pump the fuel out of the fuel tank and in to the carb using a pumping diaphragm - the one under the alloy cover held in place by a single screw.

 

An airleak in this area will cause issues with the idle being too fast and eratic when the throttle is closed and possible screaming at top end revs.

[adw]

That is the impulse tube and seal, as the piston rises and falls a positive and negative pulse is fed to the carb via this tube which causes the pump diaphram to pulsate, pulling fuel from the tank to the carb, the fuel cap leaking will not cause running issues just a wet leg, the tank breather is pressed into the top of the tank under the crankcase,you should see a good jet of fuel from the fuel hose when you pull it off the carb, this is norm due to the type of tank breather and should be there, if the carb is clean check the seal behind the flywheel they were very prone to blowing inside out.

[adw]

Sorry Steve i was was a little slow typing my reply.

[spudulike]

Sorry Steve i was was a little slow typing my reply.

 

Just shows we both know our craft Andrew, no need to apologise:thumbup:

[adw]

Just been looking at the pictures again, is that bit of old wire the ht cable??