075 stihl building pressure in fuel tank

[Kfd518]

I was kind of an inclusive statement... knowing that it was so short, it wasn't going to be trackable.

So is there a difference between the machine number and the serial number? All of the references in the manual I have show this same 7 digit machine number format.

 

[AKDoug]

Modern Stihl serial numbers are 9 digits long. If it isn't a 9 digit number, I don't believe it is traceable outside of contacting Stihl directly.

 

[Kfd518]

Got is thank you sir for the clarification. Blue mountain states they have no way to track it being as it was sold originally way out of their service area

 

[Kfd518]

Still waiting for oil pump worm oil seal to come in…stihl 9642-003-1440 backordered from stihl as well as the anti vibe mounts under the handle assy. 2-3 week availability 1.5 weeks down can't re-test till it get is hopefully this is the problem. Went ahead And replaced fly wheel side and clutch side main oil seals while in there.

 

[Willeywoodcutter]

I know this is an old thread but what were the results..I have an 076 that builds pressure or something in the gas tank and causes it to cut out any help wood be appritiated.

 

[Kfd518]

Don’t know what finally cured it. It got taken down to crank case halves and shaft. Both seals replaced. Base gasket replaced carb rebuilt again and all other seals replaced. Now tight to pres and vac. Runs like a top. Sorry I’m not much more help I’m thinking the lean out as well as crappy summer blend fuel was causing it to boil

 

[Willeywoodcutter]

My saw doesn't boil the fuel but seems like it is building pressure to the point you have to start it with the throttle locked. I was wondering about the fuel cap what is that little screw for do you know? Thanks for the quick reply too

 

[Kfd518]

Tank vent is there. Sounds like it’s running rich and flooding out to me if you have to lock the throttle. Check your adjustments likely low side, or could be that low side is completely clogged and not passing fuel but if this is the case it shouldn’t idle at all. I may be wrong in my assumptions though.

 

[Willeywoodcutter]

Could the tank build pressure and push too much fuel into the saw?? Saws runs and idles great until it builds pressure in the tank. Should that tank vent screw be seated tight?

 

[SEAM]

The tank vent should optimally let air in but no fuel out. Pressure build-up in the tank is quite normal and the inlet needle in the carb should be able to cope with that. The older vent systems usually were not perfect - some even start to "bubble" around the vent with a full tank - and did not cause an overly build-up of pressure.
I would check if the inlet needle (below the metering valve/lever) holds (some) pressure. If it leaks pressure building up in the tank will push fuel through the carb when the saw is not used due to changes in ambient temperature.
The venting action can be checked using a piece of hose directly on the vent holes in the cap.

 

[Kfd518]

There are at least two different styles of vent used in 075/076.

If the needle and seat aren’t holding then yes it is possible to push fuel past.

 

[Chainsaw Jim]

Back out the grub screw in the fuel cap until you can blow a little bit of air through it. Also it's normal for that style of vent to leak a little bit.