Jet Size
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,158
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From: San Diego, CA
I've never run straight pipes on an EVO or a Twin Cam with the CV40 carb.... so I have no jet comparison to point you in the right direction..
FWIW... I have a 2001 with stage I, and I'm at 2.5 turns with the mixture screw, and the OEM 45/190 jets. I did use the CV performance needle. I am pretty sure you will need to make a jet size change with straight pipes. I ran straight pipes for 8 years on my old '80 FXS, but I dumped the Keihin butterfly carb for an SU II carb on that one... I have long forgotten how I tuned that bike... it seems like a lifetime ago, and a world away...
Someone will chime in with experience with straight pipes and the CV40 carb, and give you a ballpark jet size(s) for comparison...
Until then, tune the CV40 carb using the usual protocol....
If you haven't already (or they didn't plug it in '99), drill out the plug on the mixture screw.... Then tune the mixture until it runs well... if the mixture screw is over 3 turns, go up a size on the pilot jet and start again with the mixture screw.. If it tunes OK at 3 turns or less, you've found your pilot jet size. During this phase, if you can't get it to run just right, you may need to change the needle before, or in addition to a bigger pilot jet.
After doing the mixture screw/pilot screw dance, then it's time to run it and see how it runs wide open... Then you will learn how big to go with the main jet...
I always begin and end with a mixture screw adjustment....
It may be a little hard to dial in straight pipes... they frequently have decel popping.. You can also search using lolipops in the end of the straight pipes to gain back some of the lost bottom end... Make that decision before tuning..
Here is a web site with parts and some good tutorials about the CV40 carb.....
.https://cv-performance.com/instructions-guides
Good luck with your tune...
Last edited by hattitude; Nov 25, 2022 at 10:06 PM.
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ccondon23
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Jul 28, 2007 08:45 PM
