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Discussion Starter · #1 ·
As I read service manuals it talks about performing a Crankcase Vacuume Test. How is this test performed and what special tools are needed? Most service manuals I have read talk like this test is more important than a compresion test to determine the soundness of a two stroke engine.

Any thoughts or information on this matter will be greatly appreciated.

Thanks
 

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This is generally performed to detect air leaks in the crankcase assembly. 2-cycle engines performance can be greatly impacted by the smallest air leak, so a good seal is very important.

Usually an air leak can be tracked down without performing this test. However once in awhile it can help to troubleshoot a difficult to diagnose unit. When all else fails then sometimes this test will show something when all else has failed to do so.
 

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Discussion Starter · #3 ·
Thanks for the reply 30YearTech.

How is this test performed and what tools are needed to do it?

Thanks
 

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I have always used a carburetor/crankcase tester. This puts postive pressure in engine and you can spray soapy water on engine to find leaks. You only pressure engine to 4 psi any more and you have a chance of blowing a seal out. If you have a bad leak it will not hold any pressure a small leak and it will leak down. Never use compressed air from a compressor it's just to much.

The testers are a little pricey but if you do alot 2 stroke engines well worth the price. To check you remove carb and exhaust and cover openings with leak proof cover plates which you have to make one having a hose barb in it. Then pressure engine with the gauge and hand bulb.

I've also heard of blowing smoke in the intake and checking for leaks. You do this with piston at top dead center. Smoke well come out where there is a leak. Use a cigar because it is a thicker smoke.

Check out this tester www.mfgsupply.com/m/c/32-8338.html
 

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Discussion Starter · #5 ·
Thanks for the reply's.

The problem I am having is on a Homelite Chainsaw, I cannot get the pump to draw fuel, I have put on new fuel line, installed new rebuild kit in the carb. Still I am getting no draw. How can I tell if the engine is creating any vacume to work the fuel pump? The engine has good compression. Any suggestions or help will be greatly appreciated.
 

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With the carburetor off, using an oil squirt can, put a drop or two of oil in the fuel pump pulse hole in the insulator. Pull the starter rope and the oil should blow back out of the pulse hole. If you are not getting any pulse here, remove the insulator and inspect the gaskets, test the port at the mounting point and make sure the gaskets are all lined up for pulse to flow through.

If your unit uses a fuel pump pulse hose, then you can test it the same way by putting a fuel drops of oil down the hose and pulling the rope, the oil should be blown back out the hose. If not then check the hose for any cracks or leaks. A major crankcase leak would cause the fuel pump not to operate, check the crankshaft seals and make sure they are tight in the crankcase and not torn.
 
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