Dr. Dirt’s Wrenching Tips: Running When Parked

Story and Photos by Dr. Dirt

Originally published July 20, 2012

The most common motorcycle repair I come across is a bike that won't start after it's been sitting for a long period of time. We often see these motorcycles in our favorite Craigslist ads with the disclaimer, "Running When Parked". To put it simply, a motorcycle needs air, spark, fuel and compression to start. If we check the basics we can usually get a bike running in no time.

Checking to see if your bike is getting air is easy. Have a look inside the airbox. Does the filter resemble chocolate cake, did you leave a rag stuffed in the airboot, or has a small animal decided to make a nest out of your Twin Air Bio Filter? It doesn't happen often, but it does happen, and all of the above will prevent air from getting inside your engine. After all, a single cylinder engine is just like an air pump.

To check the electrical system, remove the spark plug and ground it against your cylinder. Hit the start button or kickstarter and check for spark. If the motor turns and you don't have spark, start by cleaning the old plug or try a new one. Usually, a bike that won't turn over indicates a dead battery. Check it with a voltmeter and then try charging the old battery overnight. If the battery is good and the motor won't turn over check for a blown fuse or try hooking the battery directly to the starter motor to see if it is faulty. Starter motors corrode and oxidize when they sit too long.

Old fuel is the single biggest cause that makes a bike not start. Modern gasoline begins to break down 30-45 days after the day it is refined. To make matters worse, today's gasoline is blended with ethanol and it wrecks havoc with your fuel system when exposed to water or condensation. Start by making sure you have enough gas in the tank. It sounds obvious, but I have fixed a lot of bikes by simply filling the tank or switching the petcock to reserve. Now, take a good whiff inside your fuel tank. If it smells like varnish it's time to drain the tank and the carburetor. After you have drained the tank, remove your petcock. Remove debris from the tank and check the condition of your fuel filter. Fill the tank with fresh gas and check to see that it flows freely out of the fuel line with the petcock open. Next, reinstall the fuel line and open the carburetor drain screw to see that gas flows from the overflow. If it doesn't, you have a clogged float valve and you will need to replace or clean the float valve and seat. On aluminum framed motorcycles you will often need to remove the carb from the bike to do this. Finally, remove and clean your pilot jet. If your bike is still running rough a thorough carb clean will make it run smoothly.

Finally, a quick compression check is in order. Your bike won't lose compression from sitting but if it was bad before you put it away it won't start easily or run well. The easiest way to do a compression check is by pushing down the kickstarter. If there is little or no resistance on the kickstarter you probably need to replace the valves on your four-stroke or replace the top end on your two-stroke. A quick check of your valve clearance will verify your suspicions on a four-stroke. A leakdown test can be performed to determine the source of your compression loss. On a two-stroke, we often perform a compression test to determine the condition of the engine. Both leakdown and compression testers are available form Harbor Freight for $20-$45.

If you follow the basics it's easy to get your bike up and running again. Just check for air, spark, fuel and compression, and your steed should be running again!

Want more Dr. Dirt Wrenching Tips? Check out the Dr. Dirt section of Dirt Rider magazine, or stay tuned to the website for future stories and info. To suggest a topic for an upcoming installment or to ask Dr. Dirt a tech question directly, send an email to drmail@sorc.com, subject line: Dr. Dirt.