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[seven]

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

[Fired00d]

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.

 
Ride Safe,
Fired00d
 

[HEADPAN62]

i ran both carbs for a number of years,, i pefered the s&s..

[Hoist!]

Another vote for the S&S Super E/G!

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

Hoist!

[AMP]

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.

[HEADPAN62]

amp, you took the words out of my next reply,ride-on, headpan

[RedFXR2]

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.


[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. 

[AMP]

"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.

[radavi98]

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.

[RedFXR2]

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.

[DCFIREMANN]

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

[seven]

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. 

[screem]

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

[Hoist!]

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

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!

[AXIL]

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