do I need a vacuum piston? (slide)
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Tourer
Joined: May 2009
Posts: 401
Likes: 19
From: Middleboro, MA USA
do I need a vacuum piston? (slide)
Hey all.
I have been trying to tune in my cv for awhile. I had installed a thunderslide kit and drilled the slide per the directions 2 summers ago. Little by little I have replaced everything back to stock trying to get rid of this on and off lean condition and carb farts. Right now I am at 45/180 on the jets and I am thinking this should be good but its not. I think because I drilled the slide it is coming up too fast and that might be part of the reason I cant get things where I want them. I am going to replace the slide with a stock one and start from scratch with everything stock again.
Good idea? Opinions?
Anyone have a stock slide laying around they don't need?
Thanks
Chris
I have been trying to tune in my cv for awhile. I had installed a thunderslide kit and drilled the slide per the directions 2 summers ago. Little by little I have replaced everything back to stock trying to get rid of this on and off lean condition and carb farts. Right now I am at 45/180 on the jets and I am thinking this should be good but its not. I think because I drilled the slide it is coming up too fast and that might be part of the reason I cant get things where I want them. I am going to replace the slide with a stock one and start from scratch with everything stock again.
Good idea? Opinions?
Anyone have a stock slide laying around they don't need?
Thanks
Chris
Thread Starter
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Tourer
Joined: May 2009
Posts: 401
Likes: 19
From: Middleboro, MA USA
No, sorry, I had a brain fart. I installed a dynojet kit, not a thunderslide. But the dyno kit told me to drill out the vacuum hole in the slide to make it a little bigger. Aside from an SE AC, V&H pipes and the abortion I made out of my slide, the bike is stock. I want to stay with the 45/180 combo, just replace the slide with a stock vacuum piston or slide that I definitely will not drill. 
Sorry for the confusion t150vej.
C
Sorry for the confusion t150vej.
C
HDF Community Team
Joined: Dec 2005
Posts: 5,421
Likes: 2,621
From: NC USA
Oh, OK... had me shook up there for a minute 
I've done a lot of experimenting (and continue to do so) with combinations of "performance" CV parts and honestly, it's hard to beat OEM or something real close. I don't use a dyno just go by feel and plug reads and a drilled slide will work, but much better suited for either "on or off" throttle or a bar-hopper ride... if the bars are real close together.
Assuming you don't have a really tall cam, with a stock slide, needle (of about any size) and stock spring, a 175 may give you better mileage and will pull just as well. Problem with the drilled slide is that it raises more quickly as well as pulls higher with less vacuum. This causes you to have to run a bit richer than necessary just to overcome the imbalance of intake velocity between the slide and butterfly which is directly responsible for fuel input at the needle/main jet.
Ok, long story short - yes, get a stock slide and preferably a stock needle and jet holder (emulsion tube) and go from there.
I've done a lot of experimenting (and continue to do so) with combinations of "performance" CV parts and honestly, it's hard to beat OEM or something real close. I don't use a dyno just go by feel and plug reads and a drilled slide will work, but much better suited for either "on or off" throttle or a bar-hopper ride... if the bars are real close together.
Assuming you don't have a really tall cam, with a stock slide, needle (of about any size) and stock spring, a 175 may give you better mileage and will pull just as well. Problem with the drilled slide is that it raises more quickly as well as pulls higher with less vacuum. This causes you to have to run a bit richer than necessary just to overcome the imbalance of intake velocity between the slide and butterfly which is directly responsible for fuel input at the needle/main jet.
Ok, long story short - yes, get a stock slide and preferably a stock needle and jet holder (emulsion tube) and go from there.
Club Member
Joined: Jun 2007
Posts: 3,193
Likes: 7
From: North Atlanta Area, GA
I upgraded my CB carb with this kit from harley-performance.com. It runs great. I got their Deluxe kit with their "EZ-Just" idle adjustment screw that makes it super easy to tweak the idle mixture.
The kit came with a couple of different idle and main jets. I run the 46 idle (stock is 45 and the next stock step is 48) and the 185 main (stock is 175) - which for Bertha seems to be a perfect combo. Idle response is crisp, and she pulls strong all the way to redline.
The kit also comes with a replacement slide needle and emulsion tube. I am really happy with this kit.
The kit came with a couple of different idle and main jets. I run the 46 idle (stock is 45 and the next stock step is 48) and the 185 main (stock is 175) - which for Bertha seems to be a perfect combo. Idle response is crisp, and she pulls strong all the way to redline.
The kit also comes with a replacement slide needle and emulsion tube. I am really happy with this kit.
Last edited by NorthGeorgiaHawg; Jul 25, 2010 at 10:00 AM.
Road Captain
Joined: Apr 2005
Posts: 535
Likes: 14
From: Highspire Pa
The best CV set up I had was done by Walley Kerstetter, and back then he also sold a kit with everything you needed if you wanted to do it yourself. He will answer any questions if you email him.
http://www.harleydavcvcarbrebuild.com/
http://www.harleydavcvcarbrebuild.com/
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