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How to diagnose carburetor?

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A carburetor’s main role in the car is to use intake vacuum and supply fuel to the engine. And to fulfill its job, it relies on many add-on devices. So, if your mechanic says that there is a problem with the carburetor, there are several other devices which also need to be looked at before deciding that the carburetor needs a replacement or repair. 

When, clean and working properly, the carburetor allows the engine to start easily, idle evenly, and accelerate smoothly. Problems caused by the carburetor include hard starting, rough idle or idling too fast, poor fuel economy, etc. It is often difficult to rebuild a carburetor and expensive to replace, so it is better to check on all other add-ons.

  1. Check the choke. Sometimes a small adjustment or cleaning the choke mechanism can solve the problem. A broken choke will also prevent the engine from idling properly. A choke repair kit or a new bimetal spring is all that would be required if the fault lies with choke. 
  2. If there is too much heat near the carburetor, then you will experience hot starting problems. All you have to do in such a case is to reroute the fuel line away from sources of heat. You can also insulate the fuel line by wrapping it with insulation. Hot start problems can also be because of excessive resistance in a starter, poor battery cable connections, or a faulty ignition module .
  3. When there is too much of air and not enough fuel, the result is hesitation. It can be caused by a dirty or misadjusted carburetor, or because of a poor accelerator pump. You could also have a worn out throttle shaft. In such cases, replacing the carburetor may be required. 
  4. Air leaks in the engine can also cause hesitation, resulting from loose vacuum hoses, emission hose or the PCV system. A defective EGR valve can be another cause of hesitation. A defective distributor advance mechanism, a weak ignition coil, bad plug wires, worn off spark plugs could be other causes which needs to be rectified before deciding on the fate of the carburetor. 
  5. Check for any faulty power valve inside the carburetor. A new power valve is usually included with a carburetor rebuild kit. 
  6. The carburetor may have to be rebuilt or replaced if there are internal air leaks in the carburetor itself.
  7. Check the needle valve. If dirt enters the  valve, it prevents it from closing, which results in flooding of the engine. A carburetor can also flood if the float inside the fuel bowl is set too high or develops a leak. Floats are not part of a rebuild kit so you will have to buy a new one or a new kit.

If the problem is with the carburetor, it can be rebuilt with a kit or replaced with a new or remanufactured carburetor. Always consult your owner’s manual for specific carburetor tuning and recommendations.

If you need more help, or need specific answer for any question then try the ‘Carnity Forum’ (http://carnity.com/) section or find car businesses near you with the Carnity ‘Business listing’ (http://carnity.com/business_listing) section.

Edited by Carnity





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