Stihl BG55 compression Testing

goosemasterkl

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I have a Stihl BG55 leaf blower and I want to do a compression test on it but I'm not certain to the procedures involved. Do you have the choke open or closed? Do you hold throttle wide open? So if someone could give me some advice on this I'd really appreciate it. Thanks to anyone who may reply
 

bertsmobile1

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Like all compression tests it matters not what throttle or choke settings you use because yo continue cranking the engine till the reading stops rising.
However it will happen a lot quicker with a wide open throttle & choke off.
Normally 3 to 6 pulls as compared to 22 pulls for closed throttle & choke on.

Now be carefull about your readings.
The cylinder is only 15cc volume at tdc.
If your compression tester is 2 threads short of the end of the plug hole the combustion chamber goes to 20 cc so your reading will be 25% lower
The inverse applies if your tester is too long.
You must use a screw in tester for this reason & it must go as close to possible to the end of the thread in the head.
Otherwise your readings will not be accurate.
having said that less than 75 PSI and it will not fire.

Leak down testing is what is required for small engines and in particular for small 2 strokes.
Also both pressure & vacuum testing of the crank and the latter is more important than the former
 
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