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Buell Forum » Old School Buell » M2 Cyclone » Anyone still dealing with the "Keihin Cough"? « Previous Next »

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Captainkirk
Posted on Tuesday, July 07, 2020 - 01:36 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

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.
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Hawgford
Posted on Tuesday, July 07, 2020 - 09:54 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

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
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89rs1200
Posted on Wednesday, July 08, 2020 - 01:24 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Hawgford, What is YT in your statement; "roll through the vids on YT". I would like to know the 8 mods.
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Dhdjr
Posted on Wednesday, July 08, 2020 - 05:39 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

YT= Youtube
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Upthemaiden
Posted on Wednesday, July 08, 2020 - 08:53 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

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.
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Hawgford
Posted on Wednesday, July 08, 2020 - 07:48 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

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..
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Captainkirk
Posted on Thursday, July 09, 2020 - 01:15 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

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...
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