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Discussion Starter #1
If I was to use 2, Mikuni VM 32 mm Round Slide Carbs in place of the stock CV carbs would I gain any bottom end power/harder acceleration? I want to pull the air box lid off my piped 660 but the CV slides do not seem to like the grater air increase and give it a slower throttle response.

Thanks in advance for any help.
 

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Master of the Electron
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We all (okay, many of us) run lidless with improved performance... but it absolutely requires DJ aftermarket needles (more aggressive taper), 160 left /165 right Mikuni (or 146 L/148 R DJ) mains and 25 pilots.

What have you tried that has left you unsatisfied?
 

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Discussion Starter #3
I just do not care for the sluggish throttle response of a CV carb, I would much rather have a faster responding/harder hitting bottom mid range power that a round slide carb produces vs the CV carb.
 

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Master of the Electron
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Okay, thanks for the explanation.

Hopefully, someone here will have experience with slide carbs and be able to help you.
 

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I don't see how switching to a vintage mechanical carb is going to improve anything. It would probably be worse with no accelerator pump, and a big round slug for a slide.

There is a reason why modern carbs have moved to flat slides like the Keihin FCR and Mikuni TM carbs. They also have accelerator pumps which helps with throttle response.
 

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I just do not care for the sluggish throttle response of a CV carb, I would much rather have a faster responding/harder hitting bottom mid range power that a round slide carb produces vs the CV carb.
Jamming a carb wide open at idle isn't going to make hard hitting low end power. You really have to work with FCR's to get them to be able to do that. Other wise it just bogs and stumbles for a few seconds if it doesn't die. What type of riding would require this type of throttle use anyway?
 

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Discussion Starter #8
I don't see how switching to a vintage mechanical carb is going to improve anything. It would probably be worse with no accelerator pump, and a big round slug for a slide.

There is a reason why modern carbs have moved to flat slides like the Keihin FCR and Mikuni TM carbs. They also have accelerator pumps which helps with throttle response.

I refuse to drop $800 for the FCR carbs, and I read online on several websites that a mechanical carb would offer more of a low end power hit then the CV carbs will, but I do now know, hints why I asking.
 

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I refuse to drop $800 for the FCR carbs, and I read online on several websites that a mechanical carb would offer more of a low end power hit then the CV carbs will, but I do now know, hints why I asking.
The other problem is fitting two carbs in there. FCR's are pretty narrow per carb where individual carbs are going to be a little wider and might not be able to fit side by side.
 

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Discussion Starter #10
The other problem is fitting two carbs in there. FCR's are pretty narrow per carb where individual carbs are going to be a little wider and might not be able to fit side by side.
That is true never though of the fitment issue, DAMN I do not know then and like you said the round slides have no accelerator pump so idk... can the accelerator pump be adjusted for a bigger fuel stream maybe??
 

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can the accelerator pump be adjusted for a bigger fuel stream maybe??
On FCR's you can tune the accelerator pump in multiple ways. You can swap diaphgrams that have different length rivets so it limits the amount of travel. There is a passage that goes from the pressure side of the accelerator pump. There can be a check valve in there so it doesn't allow pressure to push fuel back in to the carb bowl. This will give you %100 squirt up to the accelerator pump nozzles. Some have brass leak jets. The larger the hole the more fuel that "leaks" back in to the bowl so less fuel goes up to the nozzles.

The raptor specific FCR's have the check valve so you cannot swap leak jets. What you can do is remove the check valve and run an adjustable accelerator pump cover. This has a thumb screw that you can adjust. Close it all the way and its like they come from Sudo. As you open it up it reduces the squirt. You want a little under a second long squirt. Factory setup they squirt way to long and will cause a bad stumble off the line when you slam the throttle open.

Here is a very good video showing the different settings.
https://youtu.be/FoWMl2zGtyU

CV carbs, and older carbs generally don't have accelerator pumps. CV carbs don't open the side fast enough to need one.

I think you would honestly be happy with the stock carbs on a piped raptor if you would remove the air box lid, and put #25 pilots with a dynojet kit in. The dynojet kit comes with softer vacuum slide springs. A lot of power gets left on the table by running on the rich side. Especially if your going to try to run older typically 2 stroke carbs. I have Keihin PWK's on my Banshee. They are a pretty big improvement over the stock mikuni carbs, and the Keihin PJ carbs they replaced. But that's on a 2 stroke which is a totally different animal. I wouldn't bother trying to run one or two on a Raptor.
 

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there is a reason why people looking for hp on these motors fit FCR's.
They are multi-adjustable to work with any tune, & they work.
I tried a few other things, but gave up & went looking.
Eventually a set came up at the right price.
Spent some time sorting them out (there were several reasons they were cheap)
But I haven't looked back.

Having said that, a well sorted set of stock carbs will get you to around 60hp, so there is a lot you can do before you decide they aren't cutting the mustard.
 

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Talking to the guys at Lectron, they were quite confident that if I built a 2 into 1 intake manifold, that a single 48mm would be sufficient for a healthy 720.

That carb with a billet bowl and cable is about $500

But it comes down to one thing buddy.
Ya gotta pay to play.
 
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