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I know the fcr carb allows for alot more gas, I think they even claim it will work up to a 770cc engine cause the carbs are 39mm. I know you dont have to remove the carb for jetting on the edelbrock but I honestly dont know on the fcr. I know they are pricey and I have heard alot of good things about it. Hopefully someone will chime in with some real life experiances with it. Good luck man. :thumbsup:
 

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I say when you get to the point where you have the head gas flowed, you should have it done to match the manifold you are going to run with the FCRs and save yourself some money in the long run by not having to get the head ported twice.

There is a tool made that is supposed to allow you to rejet the carbs on the bike but in real life you still have to remove them to change out the mains because the starter doesn't let you get the tool in there. This is useing the trinity intake though, which moves the carbs back some, if not useing the trinity intake it could be doen on the bike.
 

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When you're in need flow for more than 60-65hp and have the cash to do it. Porting makes an astronomical difference in whether you can use oem carbs or need to up the ante. OEM carbs can be modified and bored out too, but this isn't always the most cost effective thing to do and you're still stuck with CV carbs.
 

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Just so you know, 39FCRs don't have to cost 1000-1200 like you mostly see them priced. I know of one shop who sells them for 850 with the throttle cable to fit your thumb throttle....still not cheap but a good deal in comparison to what other places charge.
 

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CoalShedRacing said:
Just so you know, 39FCRs don't have to cost 1000-1200 like you mostly see them priced. I know of one shop who sells them for 850 with the throttle cable to fit your thumb throttle....still not cheap but a good deal in comparison to what other places charge.
What is that shop using for an intake manifold?
 

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Discussion Starter · #8 ·
...still trying to find out if you can jet FCR's without taking the plastics off? My buddy with a YFZ says he can ket without removing the plastics.

If jetting with FCR's is easier than the stock setup, then I wouldn't even consider a 700.
 

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Discussion Starter · #10 ·
Ok, so lets say the elevation at your house is 3500ft and you live in a mountainous area, and your quad is jetted correctly at say... 70*. At what point in elevation and/or temp change is a rejet going to be required?

If you like to ride up and down the mountains in the middle of summer and when it cools off in the fall time, would you have to rejet all the time?

Pardon my ignorance, but I don't have much experience with this quad or carbs yet.
 

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If you have the FCRs jetted on a dyno by someone who knows what they are doing, you're going to walk away with an A/F ratio of 12.8-13:1, I would never send one out the door any higher than 13.5:1.

That equals a potential altitude change of roughly 2000 ft or a temp change of 50 degrees before a re-jet would be needed to continue to run optimal. Now, I wouldn't hesitate to ride up and down a 4000ft mountain for just one day, its not like I'd stop half way to rejet or anything :lol:
 

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I feel your pain pewter, I live in AZ and where Im at its about 1500 feet. Just one hour from my house I get to sedona which is about 4000 feet and another hour im in flagstaff which is about 7500 feet. Huge difference! Thats the reason I want a 700 so bad.
 

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Discussion Starter · #14 ·
So what is the difference between the OEM carbs and the FCR's besides bore size?

BTW, coalshed: you contribute a lot of great information to this site. I appreciate it and intend to give you some business sooner than later. 8)
 

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Mikunis (oem) are a cv carb, meaning that they work off vaccum pressure created by those crappy little diaphrams in the tops of the carbs. Besides being inefficient, this method is also more prone to variations and failures.
 

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Pewter, I appreciate the thanks.

Mad explained it well. The main differences aside from the obvios size difference are

1. The FCR carbs are "flat slide" carbs and the Mikuni carbs are "round slide" , the flat slide design flows more air for the same size orafice than the round slide design.
2. The FCRs have an accelerator pump and the Mikuni does not, the accelerator pump sprays in a tiny stream of fuel when going from off-idle to hard acceleration so the off-idle throttle responce is much better for the FCRs
3. Mad already explained how the Mikuni operates off a vacuum signal from the motor but the FCRs are a pumper carb design.
4. The slides in the Mikuni are held open by vacuum so when you hit woops or a bumpy section of trail, the slides tend to bounce and that causes an unstable A/F mixture because even though the engine RPM does not change, when the slide bounces down, it puts the needle into the main jet and causes less fuel than is required to be delivered to the motor. The FCR slides are mechanicaly connected to the throttle plate and can not bounce in the rough stuff.
 

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^^ Great info mad and coal :thumbsup:
 
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