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Carburetor Spray Bar Length Adjustment

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Carburetor Spray Bar Length Adjustment

Old 08-06-2014, 08:45 PM
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jetpack
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Question Carburetor Spray Bar Length Adjustment



I had a number of carbs to take apart to clean and polish, repair or replace parts. I did not record or measure the spray bar length into the bore on a couple of them. I knew I would be having to ask this question before I removed them. There are no marks.

What methods are there to make sure when the spray bar is adjusted I am getting the best spray pattern and draw?

I know some kind of vacuum gauge can be made but would have to see one made. I only have a couple carbs to do so not looking to spend too much on materials.

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Old 08-07-2014, 02:39 AM
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1QwkSport2.5r
 
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Install spraybar into carb body and look from the bottom of the carb. The slot/orifice should be straight to the bottom. Pretty standard AFAIC.
Old 08-07-2014, 04:49 AM
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If it is the kind that protrudes in from the side, exactly half way is ideal. I always go a bit less because it chokes down the hole and I 'think' it will be faster.
Old 08-07-2014, 11:49 AM
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The opening of the spraybar is the end of the bar so there is no up or down. The body of it is threaded and can be adjusted before or after centerline of the carb bore. A lock nut secures its position.

Half way is what I was guessing but wasn't sure if that was the ideal position.
Old 08-07-2014, 04:25 PM
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The orifice the fuel fuel comes out of is centered in the venturi bore of the carburetor and faces down towards the engine. With some spray bars that only go halfway across the bore, you either center it in the middle or just very slightly off to the side, as the fuel comes out and sort of arcs over before heading down into the engine. So you are moving the spray bar to the side slightly so that the fuel spray stream gets centered in the bore.
Old 08-08-2014, 08:41 AM
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RC car engines have a similar spraybar setup except most of them just barely protrude into the bore. Some car Carburetors have an adjustment to move the spraybar in and out to tune the midrange but most of the time is never adjusted.
Old 08-09-2014, 05:47 AM
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Thanks all this is good to know

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