Keihin CV carb

[pamens]

Hello,
has anybody some infos about jetting a Keihin VC carb for a 74 Knuckle. Engine stock configuration. What inter. jet ? Is 45 ok. For the main I currently have a 175 . It runs great but is a little bit on the fat side. For the needle I do not know which one is in , can not read it.( the carb is a stock one )
So if anybody has a CV on his Knuckle can he give me some input about the jetting. This will be of great help
Pamens from Luxembourg Europe

[Ultrashovel]

Hello,
has anybody some infos about jetting a Keihin VC carb for a 74 Knuckle. Engine stock configuration. What inter. jet ? Is 45 ok. For the main I currently have a 175 . It runs great but is a little bit on the fat side. For the needle I do not know which one is in , can not read it.( the carb is a stock one )
So if anybody has a CV on his Knuckle can he give me some input about the jetting. This will be of great help
Pamens from Luxembourg Europe

I guess it may depend on the size of your engine. I used a CV Keihin on my former stock 80" Shovelhead for close to ten years. It was a stock carburetor with accelerator pump. The needle was stock and I used a 48 mid jet and a 160 (stock) main jet. It ran very well indeed. It's important also to get a good adjustment in the idle mixture screw. That will make the bike too rich if it's set wrong.

[patmen]

Hello Ultrashovel,
the engine displacment is 74" . I will try a smaller main jet to see if this helps. The 175 seems to be a little to big , when you say you had a 160 on your 80" shovel.
Pamens

[Ultrashovel]

Hello Ultrashovel,
the engine displacment is 74" . I will try a smaller main jet to see if this helps. The 175 seems to be a little to big , when you say you had a 160 on your 80" shovel.
Pamens

Yes, many owners believe that an extra  large main jet is needed to gain performance. That may or may not be the case, depending upon engine size. One way to determine if your main jet is correct is to do a high speed pass and a quick plug check. I carry a plug wrench and do about two miles at high speed. (Did I say high speed?) Then I shut down the motor and park. Quiickly removing the plugs will tell you if the jetting is correct. The plugs should be a nice tan color.

The main jet controls high speed. The idle jet and mid jet are in play for most of your riding. The mid jet especially controls a great part of the range of your carburetor. The idle jet is under an aluminum "EPA" plug that needs to be removed to access it if your carburetor is still original. I drilled a 1/8" hole through the round plug and took it out with a sheet metal screw. Careful that you don't drill beyond the plug or you will ruin the idle screw. It needs to be around 1 to 1-1/2 turns out. It pays to check to see if the little O-ring is present on the idle srcew, too. To set it, get the engine running at a hot idle and screw the idle jet in until tne engine falters. Then open the jet until the idle is regular and smooth. That's about right. You need a tiny screwdriver to adjust this jet.

When I first got my CV, it had a stock Evo #42 mid jet. The Shovelhead wouldn't even run above idle with that. I tried a 45 and it was OK but not great. With a #48 it was just right. The original Shovelhead (non CV) Keihin carburetor had a 160 main jet in it so I used a # 160 Evo main jet in the Keihin and the plug readings were perfect.

Another thing, make sure that there are no air leaks on the adapter that you used to convert your CV to Knucklehead use. Also, drilling the slide hole and messing with the spring to make the slide move faster will cause the engine to "hang draft" and get entirely too much air at low speeds. The stock CV carburetor is the best carburetor ever built for a bike. Honda used six of them on their Valkryie and two on the 1500 Goldwing, two of the smoothest running engines ever built. They also used them on all of their other bikes to great advantage before they went to EFI.  So, try not to fool with the design of the carburetor.

If yours has been diddled with, toss it and get an OEM version and start all over again. Left stock, they are the best. I remember riding my Knuckleheads (EL and FL) with a Linkert Carb when I was a kid. At high speed, the main jets would tighten up and go lean from vibration and, if you ran long enough, it would turn the exhaust pipe pure white from running lean. That could ruin the engine. They were all I had at the time but I never liked them.

I even prefer the CV to my EFI Ultra for idling. While the EFI starts perfectly, it idles too high. It's set at 1,000 rpm and I prefer a lower idle, around 800 rpm, but you can't set the EFI. No cigar. LOL

Another good thing about the CV is that they are tight and close down all the way when you are starting the engine so you get no extra air to spoil your starting. My Shovelhead would always start at just a touch of the starter when I had the CV on it. The old Keihin (non CV) would suck so much air, it was a chore to get it to start and the idle was rough. With the CV it idled like a little clock. With a kick starter, you really need a well-tuned engine, too.


Good luck.

[ricochet]

I have a 61 inch knuck with a non stock cam and some mild porting mostly in the intake track and manifold.  Currently using a #45 and #165 main and have a sportster needle (I think).  Seems about right on the main as plug color is a darker tan but could still use a bit more work on low to midrange.  Runs good, just not tweeked to the max yet.   With the pipes being pretty open and a modified S & S air cleaner it really breathes well.

ricochet

[Ultrashovel]

I have a 61 inch knuck with a non stock cam and some mild porting mostly in the intake track and manifold.  Currently using a #45 and #165 main and have a sportster needle (I think).  Seems about right on the main as plug color is a darker tan but could still use a bit more work on low to midrange.  Runs good, just not tweeked to the max yet.   With the pipes being pretty open and a modified S & S air cleaner it really breathes well.

ricochet

Well that sounds like a good setup. I once owned a 1947 EL with a three and reverse. It had been a hot dog wagon with a sidecar in Chicago. It was the best bike I ever had.

I really don't think that you need the Sportster needle. As I mentioned above, the Stock Keihin CV is practically perfect for most uses.

Believe it or not, your 61" should run even better if it had some back pressure. Try it and see. Open pipes make fine tunng hard to do. I know, I know, loud pipes save lives...right. LOL.

[ricochet]

I think you're tight about the backpressure because it is running well but seems flat powerwise.  I chalked some of this up to real low compression pistons that were fitted up a few years ago.  They were what was available at .040 over at the time and certainly had a lower dome than what came out but had to be used.  I have two needles available.  One came out of a sportster carb and the other was an evo but came in a carb that had been screwed with and had a few washers under it.  I used the sportster one but even that did not have the same numbers on it that everyone says to use.  I don't have it here but will look.

ricochet

[Ultrashovel]

I think you're tight about the backpressure because it is running well but seems flat powerwise.  I chalked some of this up to real low compression pistons that were fitted up a few years ago.  They were what was available at .040 over at the time and certainly had a lower dome than what came out but had to be used.  I have two needles available.  One came out of a sportster carb and the other was an evo but came in a carb that had been screwed with and had a few washers under it.  I used the sportster one but even that did not have the same numbers on it that everyone says to use.  I don't have it here but will look.

ricochet

I hate to admit it but the best that my 1982 80" Shovelhead ever ran was with a CV Keihin and stock muffler. It also ran very well with a vintage SuperTrapp with 12 discs. They do need a bit of back pressure for overall performance.

Let's face it. If you want to go really, really fast, you need a Suzuki Hayabusa.

I once bought a box of CV Keihin bodies and parts at a Harley swapmeet. There were ten or more slides and half of them had the hole in the slide drilled out. I tossed those and kept the OEM ones for spares. A lot of people mess with them and get them to where they just pump raw fuel all of the time and they wonder why they can never get them dialed in.

Sometimes, less is more. That's what our new president says anyway. LOL.