| Author | Message | ||
     Captainkirk |
I tried unsuccessfully for the first few years I owned my '99 Cyclone to get rid of the "Keihin Cough"...that lean stumble you get when you whack the throttle...with limited success. I played with jetting, and replaced the stock CV-40 with a Thunderslide version, which helped quite a bit, but it was still there. Until I bolted on a Mikuni HSR-42, that is. Man, what a HUGE difference! Throttle lag...gone. Completely. Acceleration became seat-of-the-pants. That nice accel pump squirt makes start-ups much easier. Idle speed tuning on the fly (yes, you can turn down a slightly high idle at a stoplight without even looking). This thing is the cat's pajamas and if you are still dealing with the cough issue, I highly recommend it. | ||
| Hawgford |
Without going into alot of detail,the Keihin Cv is the best street carbs out there. I run them on ironheads shovelheads and even a triumph. Got an intake for a panhead in the works. The cough is notorious because of EPA crap and everything mentioned in the above post helped but did not address the cause of the problem. Theres actually about 8 mods that need done to the CV to get it right. When done it will out perform the MIK[ which IS a great carb,but a gas hog].Before you spend the money on a door stop S&S or the MIK gas hog, roll through the vids on YT and see if you can handle doin the mods yourself,if not get it to a gearhead guy like me and it can be set up to be just about plug n play... Use keihin jets, period. 48 slow 180 main as baseline.. The chinese junk is exactly that... If you want a carb set up,I can do it in under a week and its not expensive. ! oh yeah stay away from the CVP kits or the yost power tube,they do NOt solve any problems,but do help slightly,just not worth the the price. The stock parts are plenty good.Don;t get me started on carbs,lol...hawgford@windstream.net | ||
| 89rs1200 |
Hawgford, What is YT in your statement; "roll through the vids on YT". I would like to know the 8 mods. | ||
| Dhdjr |
YT= Youtube | ||
| Upthemaiden |
I know I've seen a couple mods people have done to them... the spot that needs filed on some forcewinder intakes, some people have drilled a hole in the slide which I think was up for debate. I'll look around, but if anyone finds and good videos before I get around to it, please post a link. I'm sure there's a million to skim through. Hawg, just out of curiosity, what does a carb setup go for? My bike actually had the opposite problem when I got it, no stumble when I whack the throttle, but it did have a bad cough and stumble when I was just sitting at around 3k rpm at a constant speed. Basically right in the commuting rpm range, which was obnoxious. I finally fixed it with a couple shims under the needle. It ran pretty well, but then I switched back to the stock exhaust and I don't think I ever got it quite dialed in. I initially dropped the jet sizes, then actually worked my way back up to I think the same exact sizes I started with. I guess thinking about it, it does feel a little winded when I go full throttle. Hard to say if it's just the reduced power from the exhaust switch, but I definitely think it feels slightly winded. Bottom end and mid range are fine. I will say I certainly miss the pep it had with the V&H, and how light the front wheel always was. I prefer the reduced noise more though. | ||
| Hawgford |
If you send me a good core,I do a complete rebuild with all the mods listed on paper.Only one mod is irreversible but can be taken back to stock by replacing a part. There are no mods to the carb body it self.Without replacing the diaphragm [ these do need replacement alot] the price is $120 and includes the rebuild kit which has new intake and spigot seals. These are notorious for cookin in engine heat and causing air leaks that make the cough and sputters and bogs happen.I dont recommend going more than 10k miles on a set. I do not polish intakes or carb bodies, its worthless.You can radius corners better but rough castings help the fuel/air charge to tumble and mix,its what you want, that was the whole idea of that silly gizmo called a turbulator that came out a while back that did nothing.I can also set up a CV cab to be direct bolt on to a shovel or ironhead with a custom machined flange.If you have already rejetted the carb i wont touch it, but its still runnin the stock jets I will upgrade ,then it will be up to you to fine tune depending on equipment and altitude but most carbs modded require little to no tweaking. Other than upgrading to the SE brainbox, I recommend the Dynatek 2ki ignition and wires which can be set single or dual fire,with a 1000rpm bump to the rev limit and Autolite plugs. FOr serious race apps,the only change is to use magnacor wires/dyna race coil and either the E model S&S or addin a thunder jet fuel circuit to the stock Keihin,but i've seen old school tricks like a boost bottle work quite well over the cost of a thunder jet.Bottom line is simply this.Hd used keihin carbs for decades,why? because they were easy to make compliant and cost efficient. they could have used MIKs back in the day but they didn't. when they got rid of the butterfly style,they still stuck with a keihin.why? because its on a STREET bike.Theres no need to put race parts on a bike you enjoy on the street at different RPMs,Harleys have always been low power and comparable torque because it IS the number #1 street bike on the planet and always will be no matter what style you ride.. | ||
| Captainkirk |
Hawgford, I agree the Mikuni can be a gas hog. Anything with an accel pump is gonna use more gas, especially if you are a throttle jockey like me.  Also, the CV is auto-adjust for altitude compensation; no problem for me here in the midwest but for those who live in areas where altitude is an issue, the CV is a better choice. That being said, the CV needs the mods you speak of to make it a good performer. The Mik is a performance carb right out of the box. Once dialed in, it's spot-on. Speaking of which, dialing in the Mik is a piece of cake, as you can change main jets without dropping the float bowl by removing the drain/access plug in the bottom of the bowl. For a touring bike or bar cruiser, the CV can be tuned and messaged to perform quite well. For a hooligan bike, and a rider that demands immediate performance without a lot of twiddling the Mik was just the ticket for me. YMMV... | ||
| Victory |
In 1993 they changed the accelerator pump knozzle on the Screaming Eagle fixed butterfly carb. On Big Twin and Not Sportster ... Can you actually ••••••• BELIEVE IT ( first EPA shot i got ) I know because I managed to break my nozzle so when i got the replacement I drilled it larger eventually. The EPA version was a very negative result on throttle response and I can see something like that causing a cough. For Harley CV I always give this link. It has helped a lot of riders with cv mods that they desperately need. http://www.nightrider.com/biketech/ CV Mod http://www.nightrider.com/biketech/hd_cv_mods.htm (Message edited by victory on April 17, 2023) | ||
| Ratbuell |
I've never had a problem with a properly-jetted CV. Large (and that's what these are - LARGE) v-twins don't like when you "whack" the throttle, period. It's not necessarily a fueling issue, but the fact that you have LOTS of reciprocating mass inside the engine, and big pieces of material simply don't change speed or direction quickly. It's physics. If you "blip" an IL4? It'll rev...because those pistons are the size of our intake valves, and they can change speed and direction much more quickly. Properly jetted, all my Buells have rev-matched for quick downshifts with zero problems. I don't sit there and blip the throttle to make noise at a light, all that does is use fuel. But for actually RIDING the motorcycle? They work just fine, and have for years. | ||
| Victory |
My 80 inch race cam panhead loved that accel pump. instant roar. i almost cried when that shit epa port was installed. An entire investigation with EVERYBODY was launched  | ||
| Xldevil |
A good guidance how to modify the CV,IMHO. http://www.nightrider.com/biketech/hd_cv_mods.htm Cheers,Ralph | ||
| Falloutnl |
I went from the Keihin to a Mikuni and on my S1 Lightning (with a 1250cc Hammer kit) and can confirm that it is much, much better. I will readily admit that my knowledge of and experience with carb tuning is crap, so I will not deny that the CV might be better if you get it absolutely right, but yeah. For me it was a lot easier to just get the Mikuni. It turned the S1 into an absolute weapon. | ||
| Tonyd |
Ditto. I just installed an HSR 42-11 Easy Kit and it was the best thing I ever did. I bought my M2 new in 01 and this has completely transformed it for the better. | ||
| Kc_zombie |
What main jet are y'al running int the Mikuni? | ||
| Captainkirk |
KC-I don't recall the exact sizes any more...after all it's been almost 20 years now! I installed the 42-11 Easy Kit and it most likely would have run spot-on right out of the box but I also did the Buell Race Kit and Andrews N8 cams at the same time...so you can see why I needed to step up. IIRC it was only one or two jet sizes...nothing radical. Just remember, the Mik has an AIR idle screw, not a FUEL idle screw so adjustment is OPPOSITE of what you are used to if you go that route.(Installing the Mik) | ||
| Captainkirk |
Also, nice feature of the HSR is that you can change main jets without pulling the float bowl. I did some write-ups on here when I changed it noting some things you have to do when installing the HSR on a tuber Buell...such as rerouting the throttle cable a bit. If anyone needs that info I'll see if I can dig it up. | ||
| Upthemaiden |
How big of a change in elevation can the HSR carbs really handle? I know elevation changes seem to be one of the selling points of CV carbs. Everyone makes it sound like a great upgrade, but I live in a pretty hilly city where the elevation goes from about 710' to 1370'. I know it's no Pike's Peak or anything, but would that cause any issues with jetting? | ||
| Captainkirk |
Can't say for sure as we are about 727AGL here and the locale is fairly flat. I wouldn't think a 700ft elevation change would affect you that bad. My brother has taken his HSR'd 97 M2 on some long rides north around the lake and crossed over Lake Michigan on the ferry and never had any complaints. Where are you located? | ||
| Upthemaiden |
I'm in Pittsburgh. | ||
| Captainkirk |
I honestly doubt you would see a noticeable difference in that area. Switching over to the HSR was one of the best mods I've done. If you go that route look for the HSR42-11 Easy Kit which is specifically designed for the 1200 Sportsters and Buells. You do have to reroute the throttle cable to the left side of the frame to avoid kinking the cable and IIRC I had to reposition the VOES for clearance. | ||
| Upthemaiden |
I always hear how much more people enjoy their bikes after that switch. I still feel like I don't entirely know what it changes. I don't assume it gets the bike any extra HP, just makes it a little more responsive with less lag after you twist the throttle? I don't really have any complaints with the CV, but my bike is due for a full rebuild someday when I have another bike to ride and some time to actually mess with it. I'd love to switch to a 1275 kit and some head work, I'm sure the carb would go great with that. | ||
| Captainkirk |
I once heard the HSR referred to here on the BadWeb as "a direct connection between your wrist and the rear tire". I heartily agree.The flat slide design was designed from the get-go as a performance carburetor. Properly tuned, throttle response is instantaneous with not a trace of bog or hesitation, nor 'throttle lag' for that matter. Installation should not take more than a couple hours at the most, probably an evening's work and you can be out tuning the next day, if needed. |
