Now that I'm not driving 300 miles to visit my kid at college I will delve into the topic this thread has derailed to. Perhaps I should start a new thread, but I'm not too smart some times. I didn't read every post on this thread, so I may be late to the party.
My methods are as follows. I vacuum check first. It is the most important. A saw creates a vacuum when it runs, so it's the test that matters. I have had saws that have failed vacuum first, but passed pressure due to seal lips moving back and forth. This has only happened twice in my shop that I recall, but it has happened to me.
To block off the intake and exhaust I use the Stihl pieces supplied in the Stihl required tools that I had to purchase when I became a dealer. For all other model saws I make my own block off plate and seals. I often use inner tube material from heavy duty tubes used on heavy equipment for sealing rubber. I require a saw to hold vacuum or pressure for 15 minutes to call it good. I have performed vac/press tests on saws that would only hold for a minute and still ran fine and had no tuning issues.
Like I said above, I first apply vacuum. It doesn't take much of a leak to give you trouble pumping the pump. If I have a massive leak like this I generally switch right to pressure and attempt to pump. If it's so fast that it leaks down quickly, it becomes a wrestling match trying to pump and squirt soapy water fast enough. On a slow leak, obviously, I will just use the pump. On faster leaks I will use my compressor regulated to 10psi and use the spray bottle. On leaks that I can't seem to reach with soapy water I will dunk the saw in a Rubbermaid tote full of water. I have not issues do this with even the flywheel and ignition attached. They are designed to be weatherproof and a quick dunking shouldn't hurt a thing. With pressure applied, no water will enter the inside of the saw.
At this point I usually have identified the issue. On saws that have slow leaks, make sure you reef on the saw against it's AV, this will often reveal a leaking intake boot as well as some impulse hose leaks.
On those two saws I had a vacuum leak, but not a pressure leak, they were both crankcase seals. For those I laid the saw on it's side and dribbled a little bit of mixed gas onto the seals, when I applied vacuum I could plainly see it being drawn into the seal.
The other way to check for vacuum leaks, one that I commonly use on snowmobiles and motorcycles, is to spray non-flammable brake clean around the likely areas of leakage. An engine will change it's tune or stall when it pulls in the brake clean. My dad uses starting fluid and listens for increase in RPM. How he hasn't blown himself up yet, I don't know. Of course, the damn thing has to run to be able to accomplish this. Usually, my vac/pressure test (I refuse to call them leakdown tests) is used on non-running engines.
The other good use for a good vacuum/pressure pump is to test fuel lines and fuel tanks. A fuel tank should hold pressure and not allow vacuum to build. Often, I will test from the filter end. If it holds pressure both the needle in the carb and the fuel line are good to go.
That's it in a nutshell. All this info is available with a search around here. I don't think anything I do with vac/press is rocket science or controversial. The only thing I find worthy of debate is that I probably vac/press check too often according to some builders around here.
My methods are as follows. I vacuum check first. It is the most important. A saw creates a vacuum when it runs, so it's the test that matters. I have had saws that have failed vacuum first, but passed pressure due to seal lips moving back and forth. This has only happened twice in my shop that I recall, but it has happened to me.
To block off the intake and exhaust I use the Stihl pieces supplied in the Stihl required tools that I had to purchase when I became a dealer. For all other model saws I make my own block off plate and seals. I often use inner tube material from heavy duty tubes used on heavy equipment for sealing rubber. I require a saw to hold vacuum or pressure for 15 minutes to call it good. I have performed vac/press tests on saws that would only hold for a minute and still ran fine and had no tuning issues.
Like I said above, I first apply vacuum. It doesn't take much of a leak to give you trouble pumping the pump. If I have a massive leak like this I generally switch right to pressure and attempt to pump. If it's so fast that it leaks down quickly, it becomes a wrestling match trying to pump and squirt soapy water fast enough. On a slow leak, obviously, I will just use the pump. On faster leaks I will use my compressor regulated to 10psi and use the spray bottle. On leaks that I can't seem to reach with soapy water I will dunk the saw in a Rubbermaid tote full of water. I have not issues do this with even the flywheel and ignition attached. They are designed to be weatherproof and a quick dunking shouldn't hurt a thing. With pressure applied, no water will enter the inside of the saw.
At this point I usually have identified the issue. On saws that have slow leaks, make sure you reef on the saw against it's AV, this will often reveal a leaking intake boot as well as some impulse hose leaks.
On those two saws I had a vacuum leak, but not a pressure leak, they were both crankcase seals. For those I laid the saw on it's side and dribbled a little bit of mixed gas onto the seals, when I applied vacuum I could plainly see it being drawn into the seal.
The other way to check for vacuum leaks, one that I commonly use on snowmobiles and motorcycles, is to spray non-flammable brake clean around the likely areas of leakage. An engine will change it's tune or stall when it pulls in the brake clean. My dad uses starting fluid and listens for increase in RPM. How he hasn't blown himself up yet, I don't know. Of course, the damn thing has to run to be able to accomplish this. Usually, my vac/pressure test (I refuse to call them leakdown tests) is used on non-running engines.
The other good use for a good vacuum/pressure pump is to test fuel lines and fuel tanks. A fuel tank should hold pressure and not allow vacuum to build. Often, I will test from the filter end. If it holds pressure both the needle in the carb and the fuel line are good to go.
That's it in a nutshell. All this info is available with a search around here. I don't think anything I do with vac/press is rocket science or controversial. The only thing I find worthy of debate is that I probably vac/press check too often according to some builders around here.
