Did carb mods, but slide drilling question

2 replies to this topic
  • chicagobikefan

Posted January 12, 2006 - 08:15 PM


Just got my 55/158 jets. Changed to K&N air filter, removed snorkel, shimmed needle about .030, put in aforementioned jets, but did not drill the slide. I wanted to only do the things that were reversible just in case. Wow, what a power difference; I'd say about 20% more power at least. Wheelies much more easily. Starts easier, runs better. (The bike is louder with the intake less restrictive.)

BUT, I have a question. What does drilling the slide holes out *do*? I can't even figure out why the two non-centered slide holes are there. How does drilling them out affect the bike's performance? Any carb experts out there?

(P.S. I have a Supertrapp IDS2 quiet muffler on order (it's backordered :applause: ) When I get it, I'll try to make a video of its installation and post it.)

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  • goblin127

Posted January 12, 2006 - 08:55 PM


The hole/s are to alow air to pass through the slide so that it will open and close. Gives it better throttle response, less lag.

  • XR650L_Dave

Posted January 13, 2006 - 09:10 AM


The slide/diaphragm is just like that on a carbed street-bike, commonly called a CV (constant velocity? vacuum?) carb.

The throttle is the little butterfly in the intake, just like on a carbed car.

When you open the throttle, some air rushes through despite the fact the slide is closed (and of course the XRL has a small cam that manually opens the slide a little).

This air passing through creates an area of lower pressure, sucking air out from above the slide. This vacuum is what pulls the slide open.

The larger the holes in the slide (up to a point) the quicker that 'vacuum signal' can suck the air out from above the slide, and the quicker the slide opens.

Note that enlarging the holes does not make the slide open further during a steady-state condition.


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