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Finding the source when you have engine problems

If an engine that has been sitting for several months fails to start, don’t automatically assume the carb is the problem. There are some other basic checks to make before tearing into a rebuild. Some old mechanics used to say “most carb problems are electrical.” What they meant was what people often assume is a fault with the carb usually turns out to be something else, like no spark.

It takes four things to make a bang inside engine cylinders: fuel, air, spark and compression.

First, it’s easy to ensure you have spark. An inexpensive in-line spark tester inserted between a spark plug and lead wire will show if electricity is getting to the plugs. If you don’t have one of these gadgets, remove one spark plug and set it down on the engine so it grounds. Then crank the engine over and watch for a spark. Removing the plug isn’t always as good an indicator as using that in-line tester tool I mentioned, because creating a spark inside a pressurized cylinder is more difficult and requires a stronger current than in the regular atmosphere. (The tool compensates for that.) So a weak current may cause the plug to fire outside the engine but not inside the cylinder. But if that’s the best you can do, do it.

If that checks out, make sure you have fuel at the carb inlet. If there is a clear-bodied fuel filter on the line near the carb, fuel should be visible inside it. If not, you’ll have to crack the fuel line at the carb inlet and see if there is fuel there. But be careful doing this, it will leak out fuel if the pump is supplying it; and you don’t want to burn the shop down.

On those carbs with a pump to aid in rapid acceleration, you may be able to just look down the barrel and have someone pump the pedal to see if fuel squirts out. If it does, there’s fuel in the float bowl.

Also, check for restrictions at the air filter. Remember vehicles that sit unused for a while seem to attract mice, who love to build nests in the most unusual places.

If all of those things seem to be OK and rebuilding carb still doesn’t get the engine running right, you may want to do a compression test on the engine cylinders to ensure there isn’t a more serious engine problem at play.

About the author

Machinery Editor

Scott Garvey is the machinery editor for Grainews.

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