Chainsaw Repair

I have the Mityvac 8500 which is pressure and vac. But they are around $67.

http://www.ebay.com/itm/Mityvac-8500-Silverline-Elite-Hand-Vacuum-PumpTest-Kit-MV8500-Mity-Vac-/231018477698?pt=Motors_Automotive_Tools&hash=item35c9c63882&vxp=mtr

I also have a Mityvac II which is plastic and like the one at Harbor Freight.

http://www.harborfreight.com/mityvac-vacuum-pump-39522.html $36.99

Study the pictures very carefully so you can see the differences in the gauge of the combination models with the little twist valve on the left side where you change it from vacuum to pressure. The cheap vacuum only one doesn't have a change-over valve and the gauge only reads vacuum. But there is a pressure port that sticks up out the top where you can plug a pressure line onto the vacuum only pump but you will need a gauge for it.

Most of these are intended for brake bleeding and the vacuum sensors on a automobile engine. You don't need all this for a chain saw. You may get by cheaper by buying just the pump itself.

Most people proclaim the HF one only does vacuum. I have played around with it and it'll do up to about 15 lbs pressure easy enough but you can not read the pressure. You will need a "TEE" fitting and a pressure gauge to make it work. The pressure gauge may set you back $15 at the hard ware? The tee fitting can be found at the auto parts but might be at the hardware too. Extra clear plastic line can be had at the hardware and they have black rubber hose at the auto parts.

When checking POP-OFF on carburetors don't bother with the actual pop-off pressure, just run 10 lbs in the fuel inlet and see if it holds for 10 seconds. Putting 30 lbs pressure in a carb inlet only serves to ruin the pump diaphragm.

On the crankcase you are using 1/2 atmosphere pressure and vacuum. That is +/- 50 kPa or 15 in vacuum or 7 lbs pressure. It is another 10 second test.

On the crankcase, the vacuum test is a pass-fail but with the pressure, you can soap the seals and other areas for leak location.