chain saw problem for 741 baus

[pjt]

Hi baus and everyone else,
I have a bit of an intermittant problem with my 3120 xp husky.
Seems to be related to the time it sits after use eg between one slab and the next.

So it goes something like this...
From dead cold starts ok and revs after initial warm up, cut slab full throttle no probs will idle ok if part way thru and then returns to full revs ok can also stop it make adjustments or whatever restart full throttle fine no probs and will do it all day.
It seems to playup when it sits for about 10 to 15 mins and has cooled down a bit
Ready for next slab... so no choke, decompress, pull, fire, grab throttle, die, burrr burr kind of noise:) repeat die, repeat die, try no throttle, starts and idles sqeeze throttle, dies, repeat, idles, sqeeze, dies, arghhhhh :~:(:(:( stand up regain breath and composure try again, pull, no throttle, idles, any throttle and it dies,
so to get it going I very gently squeeze trigger and if i hear it dying let trigger off, idles, gentle sqeeze on trigger and eventually I can get it to run.
It does exactly the same thing when it runs out of fuel... theres no need to fill up cos it's only done one slab!! halfway thru the next burr burr:doh: out of fuel:B
However if it hasn't run out of fuel, I wonder if it's a fuel vapourizing type of problem, the engine is hot enuff and with it sitting for a bit, liquid fuel vapourizes so no fuel to run. but... it idles, is the fuel for idle drawn from a different area in the carby that doesnt get vapourized?

Sitting here thinking about it, as soon as I have finished a slab I turn it off straight away, should I let it idle for a bit to cool down a bit at idle?? A hot day probably doesn't help either. And it's intermittant doesnt always do it between slabs.
Any thoughts ideas baus? and other chainsaw weilding wood nuts cos I reckon I'm not the only one with this problem
Thanx everyone in advance
Peter

[741Baus]

Gidday pjt, it sound to me that the tank vent hose is partially blocked, as this problem is not occurring all the time . the next time this happens when milling just open the fuel cap a bit and see if it picks up revs if it does its an indication that the tank vent is blocked . If you want I have a pdf of a work shop manual that covers this saw and a variety of others so pm me with your e-mail address and I'll send it to you, its not very comprehensive but gives you the general idea where every thing is situated on these saws Baus

[jaksam]

I had the same problem with my 3120 (which was part of the reason I sold it and bought a Stihl 088 Magnum :U )

Had it to the dealer several times (jets, checking breather pipes, etc) with no improvement and the general consensus was that it was somehow vapourising the fuel due to heat.

In the end he suggested I turn the saw off by using the choke ie. flood the engine. The logic being this would dump cold fuel into the cylinder and cool it down enough to stop vapourisng the fuel.

Whether the logic was correct or not turned out to be immaterial as it seemed to fix the difficulties I was having with the saw.

And then I bought a better saw...:p

[pjt]

Thanks guys, I'll try both of the suggestions and see how things go.
Peter.

[Sigidi]

Peter if it starts okay and idles, but dies when the throttle is used in those times it has sat for 10-15 min. I'd just start her let her run at idle a min or two then it should take care of any vapor issues. If it still does it then maybe you have a vent prob?

I'm no expert, so I'm just thinking a way around it.

[Calm]

I think if it is stalling when you try to rev it up it is not getting enough fuel.

What is causing it - How to fix it?

Vaporising - too lean on transfer ports/jets- accelerator pump not working - marginal/slightly too lean on the idle jet

Well it doesnt have an accelerator pump so cross that off, it probably doesnt have a transfer jet - but may have a port - could be blocked but works ok when not stopped hot.

So you are down to the low speed jet and high speed jet adjustments.

I would try to richen up the low jet on the carby a bit, this is te jet that is being used at this stage of the running.

If it is vaporising then try packing something on the exhaust side of the "carby cavity" to help stop the heat getting in. To help fix this the isdle for a bit before you rev it up should fix it.

I'm not a "expert" but i am a mechanic and a good one at that.:q

[timbertalk]

Regarding fuel vaporising, I have a Kawasaki 2-stroke brushcutter which runs well for about 10 min, then cuts out every time. Don't bother trying to start it then either, unless you want some exercise! To test whether this was due to vaporising, I filled the tank with very cold fuel (in freezer for an hour, don't worry I'm not married any more), and lo and behold, it will run for hours, until it heats up again. Two hours brushcutting is all I can take at a time anyway. Why not try this to test for vaporising?:wink: Ken

[pjt]

Thanx everyone for the tips,
My gut feeling is I need to do a few operational things...let it idle a bit, give it a few quick revs, idle a bit more then maybe choke it to flood it after a long run, one thing at a time tho, KISS might be the case here.

And when it is playing up but idling let it idle for a bit and then try to go WOT.

The other thing I'm thinking is that 2 stroke carbs don't have a fuel bowl/float arrangement like 4 stroke carbs do... therefore, Where is the fuel vapourizing from?
Could it be that the liquid fuel is pushed back into the tank by the expanding vapourized fuel?
Thoughts?
Peter.

[weisyboy]

the carby on chainsaw and whipersnippers are diaphram carby so they will operate at any angle other 2 strokes still have a bowl.

maby a problem with the intake valve anfd the cylider is pushing the fuel back?