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Please Help

mbenson72

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I have a 81' cb750 custom. Will having having the air box off make it act like its starving for fuel when you accelerate? It runs a little better with the choke pulled. But once you have reached a higher rpm like 4K it starts starving for fuel. Please help me.....
 
> Will having having the air box off make it act like its starving for fuel when you accelerate?
Yes
In general when ever you change how an engine breaths (Exhaust or Air Filters) Carburetor Jetting must be adjusted to compensate. Your 81 CB750 has cv carbs and the air box is ideal to make it run right. Use the search, there's lots of information here on tuning carbs.
 
It's a very common mistake. People think the bike looks cooler with the airbox off with out realizing they throw the whole engine out of tune by removing it.

With a lot of time and money you can get the engine to run "almost" as good as it did with the airbox on. The simple fact is, the whole thing was designed to use an airbox with those exact dimensions.

With the newer paint techniques you can have the stock one painted almost any color you want (I saw one that appeared to be blue anodized) or you can find many aftermarket airboxs that are more pleasing to the eye. They won't be exactly perfect for the engine but they are much closer then anything that doesn't have all 4 carbs share the one common air chamber.

Avoid the K&N oiled filters as it's near impossible to get the exact same amount of oil into the fabric each and every time and that will change how the bike runs too.
 
Nobody EVER runs the valves on these either and can produce the same issues when you begin to burn valves to make the engine miss at lower and lower rpm. A compression test is usually called for since so many think the engines are still in perfect shape after 35 years. Then the crying begins.

The CV type carbs HATE having anything other than the stock airbox as noted.
 
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