Author Topic: cv carb slide  (Read 2473 times)

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Offline harley 1998

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cv carb slide
« on: Wednesday, August 18, 2010. 06:53:05 AM. »
hello guys i need some advice on a my carb slide. i have a 1998 sportster sport i put a stage 1 jet ket in the carb runs fine, just one little flat spot. my kit didn't come with the plastic slide, some says to drill the vacuum hole out in the slide and some says not too. i do not know what to do any advice that anyone can give me will be greatly appreciated thanks.  :scratch:

Offline mayor

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Re: cv carb slide
« Reply #1 on: Wednesday, August 18, 2010. 08:43:39 AM. »
I wouldn't drill a larger hole in the slide.  I've played around a good bit with tuning CV carb's, and I've yet to find a better set-up than one with an unmolested slide.  When you drill that hole out larger, the afr gets real crazy (much less controlled).  From my experience, most of the time poor use of the "jet kits" can kill milage and actually hurt performance.  Keep in mind, the CV stands for constaint velocity.  Drilling a hole in the slide and using a lighter spring might make the carb sound like it's sucking air like a 4 barrel quadra-jet, but that doesn't mean that the velocity is still there. 

Earlier this year I did some road tuning with a WEGO afr emter on my lowrider that has a cv carb on it (the larger 44mm though), and based on afr meter readings - the light spring with an unmolested slide had a much more eratic afr pattern at cruise than the stock spring with unmolested slide.  I kept the lighter spring in it, because it brought my afr to the range I wanted to be in....but it definitely provides much less control on the slide than the stock spring. 

I've done a good bit of road tuning by feel with my carb bikes, and one thing I noticed was tuning by seat of pants is very subjective.  If you're going to tune that way, make sure you understand the signs of rich and lean....even that doesn't make up for a true afr reading by an afr meter.  When I road tune carb bikes I base everything on feel and how the exhaust sounds (tone), and even then I've been wrong based on afr meter readings.  I think it is very easy to mistake overly rich for not being rich enough when you are tuning a bike by feel, if you're not paying attention to what your engine is telling you. 

hope this helps,
warning, this poster suffers from bizarre delusions

Offline PC_Hater

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Re: cv carb slide
« Reply #2 on: Wednesday, August 18, 2010. 01:44:24 PM. »
Put the bike on a dyno to find out what it does.
Once you know that there is a real problem and what it is you can try and find out how to fix it.

The dealer I bought my first Sportster from made a mess of the Stage 1 tune using a DynoJet kit. I could tell it wasn't right.
The dyno proved it. 16bhp hole in the mid-range.
Luckily dyno-man knew to call DynoJet and they talked him through fixing it.
1942 WLA45 chop, 1999 FLTRI, 2000 1200S