Vacuum test advice needed please

[Ron Trew]

Hi, I have a Stihl MS381 with an air leak somewhere.
The saw starts easily enough but revs high (about 3/4 throttle) and won't come down to idle.
A mightyvac would be useful but just for a 1 time use atm I cant justify the price.
I've ordered a hand held brake bleeder vacuum pump with a gauge.
My query is, if the saw won't hold vacuum, can I track the leak by vacuum alone? IE: Will it hiss, or bubble with soapy water etc?.
I guess I can remove the gauge and connect it to a foot pump to get a pressure test, but won't know till it gets here.
Tia.

 

[TheJollyLogger]

Honestly, you will get much better response from the chainsaw forum, that's where the gearheads hang out. Just keep scrolling down.

 

[Ron Trew]

Honestly, you will get much better response from the chainsaw forum, that's where the gearheads hang out. Just keep scrolling down.

Ok thank you. I'll post in there. Admins please feel free to delete this thread.

 

[a. palmer jr.]

If you're gonna work on chainsaws in the future you need at least a pressure test outfit, very easily made and not very expensive. Is there's a possibility on your saw that the throttle might be sticking? Just a thought. Anyway, a pressure test is a must because an air leak can ruin your saw if not seen to.

 

[stihltech]

Go to harbor freight and get a vacuum/pressure tester. Block the carb and exhaust opening with rubber gasket of some kind. Use the pulse port on the case to hook the pump line to or get sparkplug adapters off the internet. Pressure leak will show bubbles vacuum leak with most likely be seals. It will suck a liquid on top of the seal in.
I prefer dawn dish detergent and water in a spray bottle.
You can also spray brake cleaner on different places while the saw is running . Any change in behavior signals a leak. Usually vacuum first. The hose provided with the can lets you get close to specific areas.

 

[Okie]

If when you first start your saw it idles good BEFORE you give it throttle and it does not come back down to idle your throttle is probably sticking.

NEXT: You say you don't care for spending any $$'s on a vac/pressure tester.

You might want to consider these options so as to justify the cost of properly testing your saw.
Take it too a chainsaw mechanic shop and let them fix it and you PAY for their knowledge OR
Fix it yourself, for your self and get experienced enough that you can MAYBE repair your own saws and save some $$'s not just today but in the future doing FUTURE repair testing.

or just get out your plastic cards and go buy new like lots of folks do now days.

I've got a $10 blood pressure bulb that goes to about 5 lbs can be used for pressure testing a chainsaw block, but I have a Mityvac pressure/vac 8500 that I use also and the mityvac is also used for testing several other mechanical things, like autos, ATV's, UTV's. Auto HVAC controls.

In answer to your question: It's usually more user friendly to FIRST test a chainsaw block with about 5#'s of pressure and use soap to look for bubbles. Just imagine trying to find a leak in a inner tube or tire by using vacuum instead of pressure.

 

[Ron Trew]

In answer to your question: It's usually more user friendly to FIRST test a chainsaw block with about 5#'s of pressure and use soap to look for bubbles. Just imagine trying to find a leak in a inner tube or tire by using vacuum instead of pressure.

This is the type of answer / advice I was looking for as if you read my op you'll see I will get pressure to the case. So thanks for that.

Not all the other crap you posted from your high and might soapbox.

 

[TheJollyLogger]

Yeah, g'day mate, dont let the door hit you on your way out.