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Harley Davidson Intake Leak Symptoms

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There are a couple of general issues you’ve got to be prepared to face when dealing with engines. From mechanical to electrical, natural, and even human causes, machine problems suck. An intake leak is one of those issues you have to expect when using a motorcycle.

How do you diagnose an intake leaks? What are the Harley Davidson intake leak symptoms you should look out for? Can you still drive your motorcycle with an intake manifold leak? How do you fix them before they get out of hand? These and many other pieces of information you’ll come to learn in this short post.

What is an intake leak?

An intake leak usually occurs when there are cracks in a portion of the intake tract beyond your fuel delivery system. The leak can occur anywhere between the cylinder head and the carburetor slide. When this happens, the intake manifolds sucks outside air in, rather than dispersing air out. This can cause performance issues including poor fuel economy, decreased acceleration, and engine misfires.

Best Air Intake for Harley Davidson

How do I diagnose intake leaks?

There are a few ways to figure out if there is a leaking intake manifold.

  1. Tug the clutch in and close the throttle. Naturally, if there’s an intake leak, the engine revs drop immediately.
  2. Check for the leak itself, ignite and start up your motorcycle, and allow it to idle. Get a bottle of carb cleaner. Apply the liquid in areas, and a change in RPMs is a sign you have a leak issue in your hand. This video explains it very well. https://www.youtube.com/watch?v=oKVHqCJN2LU

What are the Symptoms of Leaking Intake Manifold?

Harley Davidson Intake Leak Symptoms
Power Loss
Hesitation to Lean Issues
Engine Overheating
Low Oil Pressure
Bad Oil Viscosity
Air Intake Leaks Manifest in Several Ways

From power loss to hesitation to lean issues, engine overheating, low oil pressure, or bad oil viscosity, air intake leaks manifest in several noticeable and not-too-noticeable ways.

Usually, when there’s an intake leak, there’s a disproportionate ratio in the amount of air and fuel that flows into the engine. As a result, too, the additional oxygen mix increases engine temperature, affects (reduces or increases) engine performance, and causes the air-fuel mixture to go leaner.

High idle is one issue that readily comes to mind. You know you might have a vacuum leak in your intake manifolds if you observe that your bike suddenly starts idle higher for no particular reason.

The second one is hanging revs. This is a common and easily noticeable symptom. Hanging revs occur when the engine drops immediately after you pull the clutch in and close the throttle abruptly. When you notice this, there’s a big issue of an air leak threat. 

How do you fix an intake leak?

Here’s a piece of headline-making news: diagnosing is the most difficult part of your job when you think you have an an intake leak. Repairing the intake manifold problem is a simple and not an expensive job. If you choose to opt for a DIY process, it is fine, but, why not try to engage the service of a professional? In that way, you wouldn’t have to repair and replace, over and over again.

To fix the issue, you need to seal the cracked part before you start up your engine, and guess what, your motorbike engine is back to full capacity. Blowing the piston top may be damaging to the vacuum hoses because the latter are not often made of hard materials.

There’s also a chance that your V-twin intake isn’t properly aligned with the cylinder head. The best solution is to completely seal off the crack by reinstalling it. Loosen the head, let the intake settle to a flush position, and then tighten it.

Also, if your carburetor needs a tight seal, go for Carburetor o-rings; they are both cheap and effective on your motorbike. It is better than merely loosening the throttle shaft or applying the felt spacers on the setups.


The truth is that the earlier you diagnose an intake leak, the better. The increased temperatures in your engine will begin to cause major damage with time. The low-fuel mixture will burn fast. This would be more than your engine cooling system can manage and you can end up with a coolant leak on top and will need to do some major replacing. Here’s a piece of advice you may not get elsewhere: ‘do not use aftermarket air parts to fix Harley Davidson intake leaks. Go for the OEM air parts.’ If you’re in doubt, then try to contact Harley Davidson customer service support. Enjoy the full performance of your Harley Davidson bike, and bye for now! 

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Harley Davidson Intake Leak Symptoms

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