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CVO Technical => EVO => Topic started by: seven on March 19, 2008, 04:39:20 PM

Title: What carb on my EVO?
Post by: seven on March 19, 2008, 04:39:20 PM
I am thinking about changing carbs on my fxr4. What is the best carburetor? I know many people that run S&S carbs, but a friend of mine that works at the local Harley shop says that mikuni carburetors are the way to go. I will eventually have the heads reworked, a better cam installed, and ignition changed, and maybe high compression pistons put in. So does one carb work any better than the other when doing these mods? Any help and advice will be appreciated in this matter. THANKS
Title: Re: What carb on my EVO?
Post by: Fired00d on March 19, 2008, 05:00:11 PM
Funny you mention this... I was just reading in the April '08 Easyrider "Talking Tech" section where someone was asking this same question about comparison of these two carbs. Their reply...

Both are great carbs. S&S people like S&S because they're simply. Mikuni people like Mikuni's because they're sophisticated and don't usually mind crappy pipes too much.

 :pumpkin:
Ride Safe,
Fired00d
 :fireman:
Title: Re: What carb on my EVO?
Post by: HEADPAN62 on March 19, 2008, 05:06:25 PM
i ran both carbs for a number of years,, i pefered the s&s..
Title: Re: What carb on my EVO?
Post by: Hoist! on March 19, 2008, 06:44:48 PM
Another vote for the S&S Super E/G! ;)

I'll take that American made carb over the Jap counterpart any day! :o

Hoist! 8)
Title: Re: What carb on my EVO?
Post by: AMP on March 19, 2008, 07:20:33 PM
S&S carb will work great(probably the best) for wide open and top HP applications. The Mikuni is more "fine tuneable" for everyday riding. It gives you a smoother fuel delivery, more controllable.
Title: Re: What carb on my EVO?
Post by: HEADPAN62 on March 19, 2008, 07:38:31 PM
amp, you took the words out of my next reply,ride-on, headpan
Title: Re: What carb on my EVO?
Post by: RedFXR2 on March 19, 2008, 07:41:15 PM
Ahhh, the carb question. 

I am thinking about changing carbs on my fxr4. .... I know many people that run S&S carbs, but a friend of mine that works at the local Harley shop says that mikuni carburetors are the way to go. I will eventually have the heads reworked, a better cam installed, and ignition changed, and maybe high compression pistons put in. So does one carb work any better than the other when doing these mods?

To start my $.02 worth, AMP wrote what I have been told by experienced HD techs.

S&S carb will work great(probably the best) for wide open and top HP applications. The Mikuni is more "fine tuneable" for everyday riding. It gives you a smoother fuel delivery, more controllable.

However, those same techs went on to ask me if I really needed a new carb...what kind of riding was I going to do and how far was I going with my motor makeover?  Because they could re-jet my stock CV to match the heads and cam just fine.

I have SE heads (instant 9.5:1 compression) stock pistons and bore, EV27 cam, SE lifters, SE ignition module, coil and wires. I went into this project with a Mikuni carb on my wish list but the techs talked me out of it.  They agreed that I could save myself $500 by re-jetting the CV carb.  What AMP said is apparently true--more tuneable, better fine adjustment, more even fuel delivery.  Theyre great carbs.  But I had to ask when I was going to "feel" all that with my riding style.  There's something really sexy about those Mikuni carbs, while S&S seem to be thought of as oldies but goodies, but I have to say my motor sure does run good with the re-jetted CV along with all the then-new performance parts.  Would it run better with a Mikuni?  Possibly so, but would it be $500 better?  Those Techs don't think so and 1 1/2 years after the motor work I see no need for a carb upgrade.

Just thought I'd throw this into the mix.  One thought would be to do the other mods you mention first and then see if you still feel the need for a new carb.  Me, I'd prioritize the mods in order of impact.  Cam and heads first.  Unless you're going really radical with those, I doubt you really need a new carb.

Of course, this is just my opinion. ;D


[edit]

HOwever, it's not just my opinion.  I checked the nightrider.com website (lots of good info) and found the following pertaining to the stages of high performance builds for Evolution motors.  They don't recommend a carb change until stage 3 and even then, well, read for yourself:

 http://www.nightrider.com/biketech/hdbuildstage3_95.htm

“If you don’t have the money to purchase all the parts listed for this engine, we recommend you make the following changes:

Use your re-jetted CV carburetor in place of the Mikuni HSR-42. The CV is capable of supporting a 90 HP engine. Just keep your Screamin Eagle air filter clean and make sure the carburetor is well tuned.”

If a 95 HP Evo with lots of heavy duty high performance mods (read their list for this stage and stages 1 and 2 before it) doesn't need a Mikuni, then I know mine doesn't. 

Title: Re: What carb on my EVO?
Post by: AMP on March 20, 2008, 07:39:58 AM
"Would it run better with a Mikuni?  Possibly so, but would it be $500 better?"

Right on.... That is exactly the point in all these hop ups.

But that being said, this is what he asked "So does one carb work any better than the other when doing these mods?".

The goal is to get air(and fuel) in and air out. Think of these motors as big air pumps. The more effeciently you handle the air flow (i.e. volume plus velocity) the more effeciently the pump produces(more HP/TQ). If I were 'purchasing' a carb it would not be a CV. Could I make a CV work? You bet.
Title: Re: What carb on my EVO?
Post by: radavi98 on March 20, 2008, 08:09:08 PM
I will go against the grain and if you are going to change the carb, go Mikuni.  I had the 42mm on my 98 Low Rider and it was rock solid and efficient.  The guy that I sold it to feels the same. On my '03 107 I have the S&S Super G bored w/thunderjet and wish I opted for the stock 45 Mikuni. Behind the air filter nobody knows but you.  Most purists hate the Jap/American combo, but I would trade my S&S for the Mikuni any day.  But I ride the 07 Ultra with fuel injection more and do not miss the carb at all.  I thought fuel injection was selling out also at the time.  Let us know what you do.
Title: Re: What carb on my EVO?
Post by: RedFXR2 on March 20, 2008, 08:41:45 PM
If I were 'purchasing' a carb it would not be a CV. Could I make a CV work? You bet.

....if you are going to change the carb, go Mikuni. 

I think the assumption here is that Seven already has a functional CV on his FXR4.  If I had no carburetor at all, I wouldn't go out and buy a CV, myself.  I'd buy a Mikuni.  But, like Seven, I did have a CV so it made more sense to upgrade it for pennies on the dollar as compared to a Mikuni setup.

I'm not saying that a CV is better than a Mikuni, only that it makes a very cost-effective alternative for a vast majority of riders.  And as far as bang for the buck, most folks will never feel whatever incremental advantages the Mikuni may have over the CV, so for them, their $500 won't have gotten them much.

Title: Re: What carb on my EVO?
Post by: DCFIREMANN on March 21, 2008, 09:39:30 AM
Well I can tell you I would run a SE CV carb all day. For your little EVO (if it still is) you can find a 40mm or 44 mm CV's all day long. They are great and simple carbs. If you must change I would run a S/S E body with a thunder jet. The G body is too big for your motor.

Be Safe

THE DAWG
Title: Re: What carb on my EVO?
Post by: seven on March 22, 2008, 11:02:41 PM
Thanks to everyone for your advice. Sounds like just keeping my cv and rejetting accordingly is the way to go as of now for a poor guy, trying to build on a  budget. 
Title: Re: What carb on my EVO?
Post by: screem on March 23, 2008, 09:12:29 AM
Dittto on the carb upgrage..CV is a great carb and will work just fine for what you have planned...I have used all three type carbs on different bikes over the years...being the backyard mechanic that I am ...I prefer the S$S to the Mukuni, as it is much easier to dail in...plus and here is the biggie....the aircleaner is so much cooler looking :orange:
Title: Re: What carb on my EVO?
Post by: Hoist! on March 23, 2008, 12:39:04 PM
Dittto on the carb upgrage..CV is a great carb and will work just fine for what you have planned...I have used all three type carbs on different bikes over the years...being the backyard mechanic that I am ...I prefer the S$S to the Mukuni, as it is much easier to dail in...plus and here is the biggie....the aircleaner is so much cooler looking :orange:

Yeah screem! A HD motor can't look any better than with that Teardrop A/C. That classic S&S Teardrop completes any HD engine. If I could find a way to use it on my 62mm HPI TB, it'd be on there right now! ;)

Hoist! 8)
Title: Re: What carb on my EVO?
Post by: AXIL on March 24, 2008, 10:12:08 AM
ALL THE CARBS LISTED IN THIS
 THREAD ARE A GOOD CHOSE ,  WE ALL HAVE A FAVORITE,  MINE IS THE CV'S. I PUT A 51MM CV ON MY 103+ AND NEVER LOOKED BACKED
Title: Re: What carb on my EVO?
Post by: Bullwinkle on July 04, 2008, 11:54:53 AM
A few months ago I bought an FXR3 and it had a mild cam, ported heads, Crane ignition and V&H Straightshots.  It also had an S&S E carb with Thunderjet.

I took the E off and went with a CV.  On a dyno I doubt there is a HP difference.  The E has sharper throttle response, but not so much to be worth the purchase price if I had to buy it.  At least not to me.  The Thunderjet killed the mileage.  It got 40 MPG, and went to above 50 with the CV, an issue with the small FXR gas tank.

So for me, if the bike came with a Mikuni I'd keep it.  Or if I could find one cheap, maybe.  I like the CV.  They are cheap, they work well, and compensate well for altitude if you ride the mountains.  The big problem with the Mikuni is that there are too many tuning choices (I never thought that could be bad) and sometimes a good change here might cover up a bad one there and you might have a tough time getting it fine tuned.

YOu can find good Mikunis on eBay for not a lot if you are patient.

I have a nasty Mustang with an aftermarket Double Pumper carb.  The carb has removable idle and main air bleeds and four corner idle screws.  I put in smaller air bleeds and had to open the jets and turn the idle screws out.  Larger bleeds, the reverse.  I screwed with that thing for over a month and finally gave up.  Too many choices and me with no AF meter and nary a dyno within 100 miles.

My best thoughts on this:

Keep it simple if you bought it to ride and not to tinker with.

Since you already have the CV I'd tune it correctly (not hard) or if there is a bike event nearby or a good shop, spend $60-$100 or so and have it dyno tuned.  Then never give it a second thought.  You'd likely get more power out of the $100 dyno tune than the $300-500 Mikuni anyhow.

Bullwinkle
Title: Re: What carb on my EVO?
Post by: kansaskim47 on July 06, 2008, 11:19:16 PM
 :) :)           :) :)           :) :)

I changed out the CV carb in favor of the Mikuni on my 98 Road King .

The CV carb throttle shaft started wearing badly at about 45,000 miles and gave me some idle vacuum problems.

I like the throttle response of the Mikuni over the CV, and it seems to be working well past 100,000 miles.
Title: Re: What carb on my EVO?
Post by: hardluk1 on July 25, 2008, 01:21:50 PM
 If this isn't died , An s&s carb do'es not handle major elevation changes as well as cv or mikuni, the carb will run rich or lean. A cv can be upgraded with Trocks or Woods to flow better and still handle 100 hp+. A mikuni, as good as they can be if you are going for a high performance cam with enough overlap in timeing can make you think something broke in the motor with slide slap. It is a common problem with the carbs. A mikuni kit can be bought for much less than 500 dollars if you take your time look'n  can be had less than $400 but still alot of money.  Check out Nightrider performance  for cv tuneing tips. If you have drilled the slide in your cv it will never get good fuel milage again. I came to this site look'n at fxr info saw this thread . I have no cvo but have had some stout running bikes and have tried some different combos.
Title: Re: What carb on my EVO?
Post by: Classic Beast on August 11, 2008, 02:53:04 AM
I ran many S&S carbs, was totally convinced they were the perfect carb, found them to be great performers and fairly simple to tune but one problem if you happen to have a motor with reversion problems due to exhaust and cam choices they are almost impossible to tune even with the thunder jet, air bleed changes and yost power tube. I switched over to the 51mm SE CV and problem eliminated right out of the box. The next motor I also tried the S&S (because I had one) then ended up pulling it off and replaced it with the Mikuni. It seems the mikuni has the power of the S&S but runs as good as the CV during regular riding. For me I would vote the Mikuni if you don't already have the CV and have to buy a carb anyways. As far as tuning I don't find them much harder than the S&S, the CV actually has more choices as you can change the springs on the CV slide etc etc. You can download the tuning guide from the Mikuni site as it has some excellent advice on tuning. One major thing that helped me save a lot of time to get it right is the Air Fuel Ratio meter from RB racing, you mount an oxygen sensor in the exhaust hook up the guage on the handle bars and go riding it tells you exactly what is going on and can be permantly mounted.

http://www.rbracing-rsr.com/rsrgauge.htm
Title: Re: What carb on my EVO?
Post by: Hoist! on August 12, 2008, 12:40:04 AM
I ran many S&S carbs, was totally convinced they were the perfect carb, found them to be great performers and fairly simple to tune but one problem if you happen to have a motor with reversion problems due to exhaust and cam choices they are almost impossible to tune even with the thunder jet, air bleed changes and yost power tube. I switched over to the 51mm SE CV and problem eliminated right out of the box. The next motor I also tried the S&S (because I had one) then ended up pulling it off and replaced it with the Mikuni. It seems the mikuni has the power of the S&S but runs as good as the CV during regular riding. For me I would vote the Mikuni if you don't already have the CV and have to buy a carb anyways. As far as tuning I don't find them much harder than the S&S, the CV actually has more choices as you can change the springs on the CV slide etc etc. You can download the tuning guide from the Mikuni site as it has some excellent advice on tuning. One major thing that helped me save a lot of time to get it right is the Air Fuel Ratio meter from RB racing, you mount an oxygen sensor in the exhaust hook up the guage on the handle bars and go riding it tells you exactly what is going on and can be permantly mounted.

http://www.rbracing-rsr.com/rsrgauge.htm

Thanks for the heads up. I'm old school and still love the S&S Super. Never tried the Mikuni though, so what I don't know, don't hurt! ;D ;D ;D

I just put the Super E on the BLUE 3 too. Had to do it! :2vrolijk_21:

But the Rev Tech 110 going into the '85 FXWG has a Mikuni. So I guess I'll get to try one soon. It's gotta blow my mind to make me lose that Teardrop on the BLUE 3 and the Bobber! :o ;)

Hoist! 8)
Title: Re: What carb on my EVO?
Post by: Classic Beast on August 12, 2008, 02:18:34 AM
The S&S for most bikes work wonderful, it's just that odd one that you have trouble with and it's not wide open but around 2500 - 2800 cruising and just want to speed up a bit. Most of the time if your having a problem it's rich in this area due to reversion the cam just starting to come on and the S&S is changing from the intermediate to the main jet. Now if it's rich no problem you just put in a larger air bleed and the main jet comes in later but if it's too lean then you have a problem the thunder jet helps a bit and if you richen up the main or the intermediate then you start to have problems elsewhere, I found the yost power tube really works on these a simple upgrade and you can notice the change with it running smoother, not sure about anymore power but they do run better. With the mikuni you have the jet needle that you can play with plus a slow jet. So they are more flexible to cover up problems as you have 3 distinct circuits that are tuneable.
Title: Re: What carb on my EVO?
Post by: wyoung8 on August 20, 2008, 04:41:17 AM
I use the S&S I just sent it to Triple X carbs for some upgrades. Don't get me wrong I like it but I had it on my bkie since 1999. I have been very satisfy with the S&S. Some of my friend have the mikuni some S&S. They like it too. So I think it's a perference. I have had no problems with the S&S. :)
Title: Re: What carb on my EVO?
Post by: Hoist! on August 20, 2008, 07:42:01 AM
I use the S&S I just sent it to Triple X carbs for some upgrades. Don't get me wrong I like it but I had it on my bkie since 1999. I have been very satisfy with the S&S. Some of my friend have the mikuni some S&S. They like it too. So I think it's a perference. I have had no problems with the S&S. :)

wy, what does Triple X do to the S&S carb? I'm not familiar with them. Thanks. :2vrolijk_21:

Hoist! 8)
Title: Re: What carb on my EVO?
Post by: wyoung8 on August 20, 2008, 11:56:48 PM
Triple X, will bore and polish the venturi, upgrade the airbleed, install a boost kit ( ie Yost power tube), and install a thunder jet for (top end performance). Go to there site they list what the service they provide.
www.xxxcarburetors.com
Title: Re: What carb on my EVO?
Post by: Classic Beast on October 20, 2009, 01:48:51 PM
Since I wrote this I have been using the 51mm SE CV carb on 2 different engines, I must say it out performs anything else I have ever used including Mikuni and S&S, power, starting, driveability, fuel mileage, all around it just runs great
Title: Re: What carb on my EVO?
Post by: Gettinold on October 20, 2009, 04:05:56 PM
Since I wrote this I have been using the 51mm SE CV carb on 2 different engines, I must say it out performs anything else I have ever used including Mikuni and S&S, power, starting, driveability, fuel mileage, all around it just runs great

I think the SE carb is made by Mikuni, correct me if Im wrong.  ;)
Title: Re: What carb on my EVO?
Post by: Classic Beast on October 20, 2009, 09:38:09 PM
nope near as i can tell it's a kehin made for harley
Title: Re: What carb on my EVO?
Post by: Pajoe on October 30, 2009, 07:22:12 PM
In the small performance catalog Harley list both the CV as well as the Mikuni carb, and both appear to be  considered Screaming Eagle carbs

Here is the description of the 42MM model, they also ave a 45mm model listed.

Category:       Race
Part #:    29641-99
Price:    $338.68 was $409.95
Description
SCREAMIN’ EAGLE® 42MM FLATSLIDE CARBURETTOR KITS
This carburettor allows you to use your stock cables. Exclusive configuration 42mm flatslide carburettor from Mikuni American for Screamin’ Eagle. Designed and jetted to work with Screamin’ Eagle Air Cleaner and Breather Kits. Exceptional throttle response and driveability. Available in either polished or unpolished versions. For race application only. 29641-99 Unpolished. Fits ’90-’99 Evolution 1340 and ’99-'06 Twin Cam 88-equipped models. Cannot be used on vehicles equipped with cruise control.
Title: Re: What carb on my EVO?
Post by: Hoist! on October 30, 2009, 07:30:42 PM
Triple X, will bore and polish the venturi, upgrade the airbleed, install a boost kit ( ie Yost power tube), and install a thunder jet for (top end performance). Go to there site they list what the service they provide.
www.xxxcarburetors.com


Wow, I missed this. Their Super E trade-in policy sounds like a decent deal. Might be time to upgrade my 110" FXWG with one! Thanks for the info on them! :2vrolijk_21:

Hoist! :coolblue:
Title: Re: What carb on my EVO?
Post by: gsxrboy96 on October 30, 2009, 10:47:44 PM
Keihin cv is the way to go, dont believe me. lets race.  ;D ;D
Title: Re: What carb on my EVO?
Post by: Classic Beast on November 01, 2009, 12:52:23 PM
This is the one I am using and it makes a huge difference over the G or the 45mm mikuni.

SCREAMIN’ EAGLE® PRO SUPER BORE
51MM CV CARBURETOR KIT
This is the highest flowing carburetor Screamin’ Eagle
has ever tested. It will satisfy the flow need of the
largest V-twins. This Harley-Davidson® exclusive kit
is complete with carb, intake manifold, higher flow air
cleaner and mounting hardware. This is the largest CV
style carb available and has easy access to main and
pilot jets without removing the bowl. Recommended for
engines 95 cubic inch and larger. Uses stock throttle
cables. The 51mm CV Carburetor is not cruise control
compatible. For race applications only.