Bored out carb??

cr2504life · Jul 27, 2004

I was cleaning my carb out and attempting to set my float level last night and I noticed that my carb looked to be bored out. But I have never seen what one looks like after it has been bored. I will take some pictures when get home from work tongiht. I just wanted to know if it was bored that would be why the original owner had such a large jet(230 main). Does this make sence? What advantages/disadvantages arise with having a bored out carb? Thanks Ohh yeah does anyone know what the float level is supposed to be for a 97 cr250? Can i get someone to post the pics for me?? Maybe I should have put this thread in the mods and performance forum, ohh well.

reelrazor · Jul 27, 2004

Bored out carbs allow greater flow. This helps in top end power. If the engine was undercarbed in the first place you may see a benefit lower in the powerband as well.

Stock carbs are castings, but the manufacturers (keihin, mikuni) machine the venturi on a lot of them, especially in performance applications. This shows up looking as if it has been bored out(which it has, just that it has been bored to stock specs).

Usually overbored carbs are done and called 'taperbored', which means they take material from the floor and roof of the carb and leave the side to side dimension alone. This is because the side to side dimension is limited by the slide's width. If your carb measures differently from side to side than from top to bottom(measured at the downstream end) then be assured that it has been overbored.

Not sure on the float spec for that unit, but if it rests on the needle valve when it is level with the carb body(inverted) it is prolly pretty close.

cr2504life · Jul 28, 2004

here are some pics of my carb, hopefully someone can tell me for sure if it has been bored. hopefully this works
http://www.allthingsmoto.com/photopost/data/500/5250carb4-med.jpg
http://www.allthingsmoto.com/photopost/data/500/5250carb3-med.jpg
http://www.allthingsmoto.com/photopost/data/500/5250carb2-med.jpg

cr2504life · Jul 28, 2004

It kinda made sence to me why the jets were so big if the carb has been bored.

cr2504life · Jul 30, 2004

Anybody else??

ML536 · Jul 30, 2004

cr2504life said:
I just wanted to know if it was bored that would be why the original owner had such a large jet(230 main). QUOTE]

Here is my understanding of why: A carburetor does not pump gasoline into the venturi of the carburetor, it is "sucked" in by the difference in air pressure caused by the air flow through the venturi. The lower pressure caused by the fast moving air through the venturi is called the "Bernoulli effect." The ability of the pressure differential to pull fuel through the jets is called the "fuel signal".

Anyway, the faster the air moves through the venturi, the stronger the sucking effect on the fuel coming through the jets. In other words, the fuel signal is stronger. When the air speed increases, because of the increased pull on the fuel through the jets, a smaller (leaner) jet is often required to achieve the air fuel mixture.

On the other hand, if your carb has been bored out, the venturi is larger, so you have the opposite effect. Because the venturi of the carb is larger, there is less of a pressure differential, and therefore a weaker fuel signal. Larger jets are required to balance the air/fuel mixture, because the fuel is not being drawn with as much force through the jets.

Bored out carb??

cr2504life

reelrazor

cr2504life

cr2504life

cr2504life

ML536

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