Question for carb experts

[Sweetwilliebrownjr]

My bike is rich at anything less than 3k or so at wot. That's with stage 7 needles. It doesn't do it with stock needles, but I can't adjust them properly. Wouldn't drilling the slides actually make it pull the needle slower in a wot situation? It seems like it would require more vacuum, which would take more rpm, to pull them, making them pull at a higher rpm. Apparently these stage 7 needles are too aggressive to be pulling as soon as they are. Am I on the right track here? I don't want to drill them if I don't have to, but I've been fighting this for way too long.

 

[dannymax]

Just the opposite I believe, drilling allows the slide to lift quicker.

 

[Rusty McNeil]

Man if was me I would avoid drilling the slides. There's no going back.

Someone else might chime in but maybe a set of stage 1 needles might help you.

 

[Sweetwilliebrownjr]

Trust me, I don't want to drill them, but I can always epoxy and redrill. It seems to me like it would need more vacuum since the bleed hole would be bigger. You'd basically be making a bigger vacuum leak, correct? If there was no hole, then the slide would pull Super fast, if the hole was the size of a quarter, it might never pull.

 

[SpecOps13]

The slightly larger hole allows air to be pulled faster in theory opening the carbs faster. Too big and this doesn't work at all. I don't drill because I've never felt a major difference after. If it works, don't fix it is my theory.

 

[Sweetwilliebrownjr]

So, I guess I'm wrong. Where does the vacuum that operates the slide originate? I'm assuming it's coming from the hole that has the o-ring on the slide covers. Judging by what you guys are telling me, it has to be coming from the air passing over the slide in the throat of the carb, creating low pressure. Is this right? If it is, it would seem I need smaller holes in the slides, or way stronger springs. Bare with me guys, I'm learning.

 

[johnpclynch]

The small hole with the O-ring is a drain to clear out any misplaced fuel/moisture from that side of the diaphram.
The slide operates by "sensing" the difference in vaccum beween the throttle valve (slide hole) and airbox (oval intake just before the venturi) - the bigger the slide hole the quicker the vaccum will act upon the spring, too big a hole and the slide will shudder open and closed causing the engine to stumble.
A stock set of carbs has a slide hole designed for general use, the slide will move evenly and reacts relativly slowly to changes in throttle. modified slides will vibrate more and react quicker to changes in throttle

 

[Sweetwilliebrownjr]

Thanks for clearing that up. I was just confused apparently.