CV carb modifications

I have seen several examples on the internet wherein the CV slide is modified by reducing weight and cutting a 45 degree angle on one side of the slide,similar to thunderjet I believe.Has anyone done these modifications themselves.I wonder if you lighten the slide if you need to utilize a different spring or does the lighter slide negat the use of a lighter spring.Any comments would be appreciated.I want to trick out the CV to use on my stroked flathead.Thanks

http://i91.photobucket.com/albums/k309/Hilly_mj/Picture022-1.jpg

After reading hours of forum posts here I might be able to answer you...although we could both benefit from a more experienced wrencher.

The Venturi (the main giant hole in the carb where the air comes in) is a self regulating environment. High pressure outside the carb and low pressure inside the engine creates a vacuum and that is what sucks air into the combustion chamber. As the air gets drawn through the Venturi it pulls the fuel in with it. Which, I think, is also why altitude doesnt really matter with a constant velocity carb. The slide regulates how fast the air is allowed to get sucked in. As the air passes through the Venturi it 'pulls' the slide up. I THINK it does this two ways simultaneously...one way is through the oval slot just above the main Venturi opening. That slot is a port into the diaphram. As the diaphram is 'inflated' by the passing air, it raises the slide. The other way is by the angle cut into the slide itself. The pressure from the passing air pushes on the angle and forces the slide to lift. These two are both just guesses by the way.

By changing the weight, drilling a bigger hole in the offset, or changing the spring, you will significantly alter how the pressure affects the slide (good or bad). It may offer a better, more responsive throttle when you are first accelerating, but it will be difficult for the slide to self regulate properly. The carb may 'hunt' or flutter.

It seems to me that the consensus of this forum is not to drill or change the weight of the slide. A spring change may be acceptable, but be particular. Make sure you consider the source of your advice...I am just a Financial Advisor, but most of these folks are hardened pros. And what I hear them say is the CV carb can be just as tough, ballsy and reliable as most any entry level performance carbs.

Talk to Ken he is the true carb expert, I have one of his modified carbs on each of my bikes. Better than any S&S carb I’ve used. I don’t know if he still does the complete modifications or if you just buy the parts from him, I’ve had my carbs since 03, I think, and had both on a couple of different bikes in that length of time. Never any problems with them.

Thanks for your input guys,it maybe that the reduced weight of the slide may void the use of a softer spring but I wonder if the 45 degree cut on the face of the slide reduces intake turbalance and enhances fuel and air mixture .I might add this flathead is about 61 cubic inches (1000cc's),with a 4 5/8stroke , a compresion ratio of about 6 or 7 to one,and a cam lift in the neighboorhood of .395.I was thinking that with a motor with this a low of a compression ratio common to flatheads that a super light slide and light spring would really help in the motors ability to rev up quicker.Again any comments would be appreciated.Thanks again for your time.

Jrule1, Celticdodge, Welcome to the site.
Nice bike Cdodge,

Chuck is right, be careful of modifying that slide... Don't cut or drill anything, just try different springs to start off with. Ken sells a nice spring you can try. I personally found that the stock spring worked best but for celticdodge's flat head, a lighter spring may be the ticket.

Ken is out in Cincinnati at the V-twin Expo this week. He may be just coming back i think or snowed in

Here is his CV information web site that is FULL of CV info. Navigate yourself around this site.
Harley Davidson Performance


Then there is his parts web site.,, just about everything you need.
CV Performance Motorcycle Products

Thanks guys for your input,you really helped me resloving some performance issues.I plan on running at the ''Maxton Mile'' in North Carolina for the land speed record,I'll let you know how it turns out.Again THANKS for sharing your knowledge it helps us all.

Before I forget what is the concensus in regards to drilling the throttle plate to compensate for cams with lots of overlap to facilitate idle smoothness?

Had a quick look at their site they are very patriotic to say the least:

Note: Effective March 12, 2003, Wood Performance Will Not Ship to FRANCE, RUSSIA, GERMANY, SPAIN, THE PHILIPPINE REPUBLIC, or any other country that does not stand in the Anti-Terrorism Alliance with The UNITED STATES of AMERICA and support America's position on Iraq and Afghanistan.
Join in our Stand Against Terrorism.

I'll get in touch with Wood Performance,and Thanks for all your comments,really appreciate your taking the time to share your knowledge.Its funny ,the older I get the less I know.

http://i91.photobucket.com/albums/k309/Hilly_mj/Picture002.jpg

But don't forget, if you don't have the big bucks needed to buy a complete carb from Wood Performance you can always modify your own carb with parts from this great web site that is run by a friend of this forum.

I got quite a few parts and information from this site and can't say enough about how much it has helped.

Harley Davidson Performance