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How to diagnose carburetor vacuum leaks on your motorcycle

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Uploaded on Feb 2, 2011

This is a simple video demonstrating the best method to detect vacuum leaks around your carb boots. Vacuum leaks are a fairly common problem in older bikes, and luckily they can usually be remedied quickly and easily, the first step however is diagnosis.

If your bike is running rough, won't rev up or has an irregular idle, before you take off the carbs and open them up, check for vacuum leaks. A vacuum leak occurs when too much air is introduced into the combustion chamber via a failure in one or more of the carburetor boots or other rubber mating surface. When too much air is sucked in, then the bike cannot combust the gasoline efficiently; there must be an optimal ratio. Therefore it is up to you to detect these leaks, and either plug them up or replace the carb boots.

In this particular bike, the engine was running VERY lean. Not only did we have vacuum leaks, but the baffles were taken out of the engine, and the previous owner had removed the air filter and neglected to install a new one. This is not only dangerous by allowing foreign material to enter the engine, but it also makes the engine run much hotter, as lean explosions create more heat than regular ones (think about blowing on a fire in your fire place: more air, hotter fire). This can be detrimental to a variety of parts in the engine, and it is a good thing we didn't ride this bike around too much before finding the problem.

If anyone has any questions as to why this is important or how to find/repair these leaks, leave a comment and I will respond.

Thank you

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