Poorman's guide to Vacuum Testing

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Under pressure

Yeah...I like to pressure test a 2-stroke CC just to get a second opinion. Nothing like some piece of mind.
 
The only problem with a vac-only test is that it's often really hard to find where it's leaking.

Pressure testing is real good to find big or hard-to-see leaks... just keep pumping and get your ear down to the saw, or squirt with soapy water. I aways pressure test first, then vac.

When vac testing, and you have a slight leak that's hard to find, flip the saw on its side and drop light oil into the seal area. If it vanishes or stops leaking, that's your problem..

I also have a low pressure regulator to feed 3-5psi air to the saw under test - much easier to find the leaks that way than pumping - you can even dump the entire power head into to a 5 gallon bucket of water!
 
Excellent!

Four Paws, great job! Thanks for taking the time to put this together. I've been wondering if a brake bleeder would work and you've answered my question! So another one... where can you buy the little nipples that you've used to connect the bleeder hose to the impulse hose. Harbor Freight as well? Home Depot? Thanks!
 
where can you buy the little nipples that you've used to connect the bleeder hose to the impulse hose. Harbor Freight as well? Home Depot? Thanks!

Yes, you can buy them at HF, Home Depot, any industrial tool supply store. Any place that sells air compressors/air tools should have them.
 
Thanks for all of the detailed info. Now I know what I'm off to do for the day. I've got an old 1716 skilsaw that has all of the syptoms of an airleak. Watch out now cause I'm armed and dangerous. The best thing to do with that first cup of coffee, a side order of AS. First cup :rolleyes: , second cup:biggrinbounce2: ,now after a side of AS :hmm3grin2orange: :chainsaw:
 
Really good job on the post Four Paws,very clear instructions. If the saw you are working on does not have an impulse line you may need another way to connect the vac or pressure line up to.I use a fitting that screws into the spark plug hole,it is homemade from an old spark plug base and a hose nipple just made them fit together and soldered them,brass to clean steel. Also use two air hold fittings that are meant to hold valves closed on four strokes if seals or springs need replacing and you don`t want to pull the head.A air hose coupler makes connecting the low pressure air supply line easy. Pioneerguy600
 
Hey
I just bought one of those pumps from the parts store today. Got the fittings and kinda gave up after that. This is the best == THE BEST post i've seen on here yet. :clap: :clap: :clap: :clap: :blob4: :rock: :rock:
 
Great job Josh! I need to vacuum test my 306A because it runs real erratic even after I rebuilt the carb. I already have a Mity-Vac, so a few fittings and I will be good to go. Thanks for the info!
 
Great job Josh! I need to vacuum test my 306A because it runs real erratic even after I rebuilt the carb. I already have a Mity-Vac, so a few fittings and I will be good to go. Thanks for the info!

By all means check it, but I had a 306a that was my main firewood saw for over 20 years and it always acted like it had a air leak when laid over on its right side.

Had to feather it to keep it running for a second then it was fine. I checked if for leaks and even replaced the crank seals. No leaks were ever found and it ran forever that way.

I think it was something in the Tilly carbs as I have a Jred 49sp that I just went through with a Tilly carb that still acts screwy when laid on its side also.

Wish I knew
 
thanks for the write up and pics...this is why I love this site. Learning all I can about working on saws. great job.
 
Seems like I've seen similar pumps that can pressure and vacuum test, but I may be wrong. Anyone know for sure?
 
By all means check it, but I had a 306a that was my main firewood saw for over 20 years and it always acted like it had a air leak when laid over on its right side.

Had to feather it to keep it running for a second then it was fine. I checked if for leaks and even replaced the crank seals. No leaks were ever found and it ran forever that way.

I think it was something in the Tilly carbs as I have a Jred 49sp that I just went through with a Tilly carb that still acts screwy when laid on its side also.

Wish I knew

Thanks, I will check it out. I really like the way this saw cuts, but I hate it when you have to stay on the trigger just to keep it running and constantly needing to adjust the carb. :cry:
 
How do you go about pressure testing the crankcase.Do all saws have the impulse line as stated in this thread to vaccum test ????
 
How do you go about pressure testing the crankcase.Do all saws have the impulse line as stated in this thread to vaccum test ????

Hi milkie62; Not all saws have an impulse line. To connect the saws that do not have impulse lines you have to come up with a fitting that screws into the sparkplug hole. There may be a fitting that can be purchased with a hose barb fitting already on it but I made mine from a old spark plug . First break out the white porcelain insulator material,a couple cracks with a hammer works well, then clean up the area where the porcelain meets the metal base. Take a hose barb, the ones I use are made of brass ,and with a little filing or a lite grind make it fit into the base where the porcelain came out and then just solder together, use flux and 50/50 solder and any torch to just melt the solder and it will join tightly. Once done you have a fitting to connect your hose up to.For pressure testing you can just run a line from a compressor or any air supply but you will have to reduce the pressure to a couple of lbs as you don`t want to blow anything apart . I have a regulator from one of my paint guns that will regulate down to zero and set it for 2-3 lbs then apply air and then check for leaks .If you have a good ear you can hear where it is leaking, apply soapy water with a spray bottle to the crank seals ,the gaskets around the carb and spacers or boots ,the crankcase halves and the base gasket under the cylinder or the head gasket if there is one,
if they are leaking it will bubble and you have found your leak.
If you just want to test the crankcase to see if it holds pressure you would also need to have a hand pump,gauge and release valve, these can be bought as a kit and connect to the saw the same as above. Pump up some pressure ,10-12 lbs works for me and see how long it will hold, the longer the better but if it is not all leaked out in 20 seconds the saw will run all right. The vacuum test works better for me as this is what the saw is subject to under operation. If it does not hold vacuum then I apply air to find the leak.
This may answer your question , it is the way I do it, other mechanics may have a different method but it all serves to find one of the most common problems with small engines. Pioneerguy600
 
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