Problems With No Spark on a Stihl BG55

Written by rich finzer
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Stihl is a widely recognised manufacturer of outdoor power equipment including trimmers, chain saws and blower/vacs, such as the BG55 model. The BG55 is powered by a 1-cylinder gasoline engine which has one spark plug. If you are experiencing sparking problems with your unit, Stihl recommends several actions you should take to restore proper engine sparking and operation.

Spark Plug Fouling

Coking or fouling of the firing electrode on the spark plug results from the excessive build-up of carbon deposits, which prevent the plug from igniting the fuel. Remove the plug, clean the electrode with a brass-bristle brush to remove the fouling and reinstall the plug. Stihl suggests that coking is often a result of poorly mixed fuel. The recommended gasoline to 2-stroke oil mixture has a ratio of 50:1. If you have doubts about the integrity of your fuel mixture, you should drain the fuel tank and replace your existing fuel supply with fresh.

Worn Plug

Stihl recommends replacing the spark plug after every 100 hours of operation. If the plug on your BG55 is worn out from old age and excessive use, replace it with a new plug. When originally built, your blower was factory equipped with a Bosch WSF 6 R or NGK BPMR 7 A resistor-type plug. Purchase an identical or equivalent replacement model. After installing the new plug, attempt to start the engine.

Bad Spark Gap

If the sparking gap distance on the plug has been compromised, the plug will not fire correctly. Remove the spark plug and check the gap with a gapping tool. The proper spark gap is 0.02-inches (0.5mm). If the gap requires adjustment, do so. Reinstall the plug and attempt to start the engine.

Boot to Plug Connection

Carefully remove the boot on the ignition wire from the top of the spark plug. Check to ensure that the threaded electrode top on the plug is tight. If it is loose, re-tighten it. Reinstall the sparkplug boot. As the metal contacts engage the electrode, you should feel the boot as it snaps into place. Attempt to start the blower. If none of these strategies resolve the problem, Stihl recommends having the blower serviced by an authorised dealer.

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