39 FCR w/ 416?

[Glamis400ex]

With the motor in my sig, with the 39FCR really make that much of a difference in power? Can anyone describe the power increase?

Looking for more GO with the mods I already have.

Thanks,

Glamis

[Iliketogofast]

I'm not really sure, but it would seem to me that if your carb can fit big enough jets to feed the engine it is already getting as much gas as it needs. Some carbs work better than others I guess, you would get throttle response probably if it is a better carb because of faster delivery.

Somebody correct me if I'm wrong (I probably am.)

[Which 450?]

Originally posted by Iliketogofast
I'm not really sure, but it would seem to me that if your carb can fit big enough jets to feed the engine it is already getting as much gas as it needs. Some carbs work better than others I guess, you would get throttle response probably if it is a better carb because of faster delivery.

Somebody correct me if I'm wrong (I probably am.)

The purpose of a bigger carb is to let in more air

[Iliketogofast]

But if you aren't going to use it what's the point? It might be there, but if your still using the same amount of fuel then you don't need any more air.

Wrong again??

[boucherbuilders]

Think of a motor as being an airpump. The more air you can get in the more hp. The fuel is used to burn the air so to speak.

[Iliketogofast]

No, that's wrong. The only reason the air is needed is to burn the fuel. It takes just the right mixture to make a good combustion, like chemistry. The air needs the gas just as much as the gas needs it.

Of course you will have more horsepower if you get more gas AND air, but you won't have any if you have too much air and not enough gas. You only need as much air as the fuel that the motor can burn efficiently.

If the bike is jetted correctly right now I can't understand why a bigger carbeurator would give it very good horsepower gains, if any. The only way I see a power increase is if the carb mixes the fuel and air better or more efficiently.

[1fst400]

anyways....

I am running a simular set up to you. I am running a 416 with 12:1 piston, porting, full exaust, stage 2 hotcams and fcr 39mm carb.

When I put the carb on I was previously running a modified stock carb with no choke and porting done.

The diffrence in the carbs was very noticible. I would say it is comparible to puting a slip on exaust on a stock motor.. or mabie a tad less.

It made the motor accelerate much stronger. Money well spent. Altho it is a pain to tune.

[400exstud]

Iliketogofast

Your a tad on the wrong side. The purpose of an engine is to burn oxygen, not fuel. By combusting oxygen and gas to form carbon dioxide and water vapor, you increase the volume taken up by the oxygen. This creates more pressure to move the piston.


A bigger carb will allow you to get more air in then you can change your jetting and be faster.

If that doesn't help think of this......what would putting a smaller carb on do?

Or

You could build your motor only so far. Then your carb will just restrict it so bad that there would be no point in doing anything else.

Hope this helped

[Rico]

Buy a 450r carb for half the cost or less and reap the same benefits of a bigger carb....:cool: They are actually 42 mm

[Glamis400ex]

Rico,

I thought 450r's came with a 39fcr? Isn't 42mm a little to big for a 416?

Glamis

[boucherbuilders]

Originally posted by Iliketogofast
No, that's wrong. The only reason the air is needed is to burn the fuel. It takes just the right mixture to make a good combustion, like chemistry. The air needs the gas just as much as the gas needs it.

Of course you will have more horsepower if you get more gas AND air, but you won't have any if you have too much air and not enough gas. You only need as much air as the fuel that the motor can burn efficiently.

If the bike is jetted correctly right now I can't understand why a bigger carbeurator would give it very good horsepower gains, if any. The only way I see a power increase is if the carb mixes the fuel and air better or more efficiently.



If your "theory" is right why is it you make more power when an engine is run lean. To much fuel (running rich) while is safer by far makes the motor lose power. Its a fact and has been dyno tested for years and years. I would know ive been dyno testing my cars since i was 18.

[400exstud]

You make the most power when your air/fuel ratio is perfect.

Running a tad lean will make more power than a tad rich but both will be less that a perfect ratio.

[cals400ex]

i do not think the 42mm would be too big. many people run it. i have seen dynos of it on a 400ex and it performed just like the fcr's. the fcr's will fit a little easier because the choke is in the way with the 450r carbs. the 04-05 450r carbs are keihin 42mm's. i do not think it is 42mm all the way through, but i am not 100% sure on that one.


we have ran fcr's on our built 400ex's. in all honesty we did not feel like it was much if any faster. the throttle pull was much nicer and much shorter so it felt faster. but when lining up at the strip we didnt see much speed difference. my buddy is running a 39FCR on his bike which is very similar to yours. he has mega top end for sure. i can not catch him on my 450r at dead top end. now, it takes him well over a 1/4 mile to catch me but if we keep them pinned that long then he will. by the way, thats even when i run a taller gearing than him. however, i do have an extended axle and it wobbles a little bit at high speed because it is so wide so i know that will really kill my dead top speed. he is also running a reverse megaphone sparks pipe which is a top end monster becasue that vacuum is pretty strong with the reverse megaphone pipes.

[cals400ex]

speaking of jetting, my buddy runs his pretty lean too because it is significantly faster when dragging. thats his choice, not mine. :D

[boucherbuilders]

Originally posted by 400exstud
You make the most power when your air/fuel ratio is perfect.

Running a tad lean will make more power than a tad rich but both will be less that a perfect ratio.


the perfect ratio is 14.7:1

usually you will try to stay away from that a lil bit just to be safe.

[1fst400]

Originally posted by cals400ex
the throttle pull was much nicer and much shorter so it felt faster.

this is one of the things I hate about this carb. it has like the equivilant of a 1/8th turn throttle for a dirbike.

It makes it hard to control the power. lol. Im thinking of taking the arm in the throttle housing and shortining it to increce my throttle throw. it is rediclous. it takes a good inch or less to go from idle to wfo. way to hard to be steady. Makes them slow wheelies a little harder to do.

[4everhonda]

I have a 406ex, Stage1 hotcam, p&p, Hmf full exhuast, vortex cdi, hmf full exhaust. The carb is great, the throttle responce is very significant. you can go from idle in first and blip the throttle and theres no bog or hesitation. It does a much better job of the air/fuel mixture and is really easy to tune. If i had to make the choice to spend the money again i defenitly would. As of the short throttle movement, its a little bit shorter than stock but not enough to bug me.

[Chino886]

I have a stock bore, stock stroke 400EX w/ hi comp piston, stage II cam, P & P, and some other mods. I have the 39mm FCR and it made a huge difference.

[aviator4]

I also have the 39FCR. I got mine from a YFZ. It's a great carb. Easy to set up and really changed the power curve. When I dynoed my bike, I change the carb ON THE DYNO and gained a little over a horse. BUT... .the torque curve changed drastcaly. Anyone who knows how to read a dyno chart will tell you that the TORQUE number is REALLY what matters. It's what does all the work. The HP numbers are great for bragging rights, but thats about it.

My HP/torque Curve did move up the RPM range by almost 400 RPM, but it get into the power faster and stays there longer.

My FCR was a major PITA to install. I had to make an adaptor for it and ended up spacing the tank up a little to get it to clear. Thumb throttle resistance is quite a bit stiffer, I don't really like that too much. I have also noticed that the throw is shorter, but only by a small amount. It doesn't bother me.

Another little funky thing that my FCR does is it "whistles" a little while lightly accelerating. I know it's the carb. Doesn't bother me but just an interesting note. oh and getting to the Choke SUCKS... at least on mine.

The FCR carb is a much more efficient design than the stock carb. I was running a 156 main in my stock carb and dropped to a 145 in the FCR to get stoichometric (14:7) then went up ONE size to run slightly right for the NOS. (all done on a Dynojet Dyno)

With the 460 Kit now installed, I've found that a 148 main in the FCR is very close to stoichometric and gets the maximum horsepower/torque from the engine. My power curve came back down as well, which is nice. The NOS has been removed from the bike. It's enough to handle without it and would be almost uncrontrollable with it on there. This ain't no drag bike!

All in all, I would say the carb would be good to accentuate the mods you have now and prep your bike for further mods in the future, but don't depend on it for major HP/Torque gains.

[4everhonda]

Yours didnt line up correct becuase it came off of a yfz...... I bought mine brand new from sparks for around $500. It lines up perfect and needs no modifications. Also my thumb throttle is way easiers than the stock one........

[Chino886]

holy snikes, you are only running a 145, I am running a 185 on mine, I better get on the dyno.

[aviator4]

Yeah, I figured being a transplant off of a YFZ is why it was a pain to put on. But then again, it was only $120... so there ya go.

185??? HOLY CRAP! I thought I was going to need a bigger jet as well. I was REALLY surprised that I went down sizes. I would think that a 185 would have your belching black smoke that smells like gasoline and you would have to be changing plugs all the time!!! Maybe I got a "weird" carb or something.

All I know is that the O2 Sensor on the dyno didn't lie

[Chino886]

Originally posted by aviator4
Yeah, I figured being a transplant off of a YFZ is why it was a pain to put on. But then again, it was only $120... so there ya go.

185??? HOLY CRAP! I thought I was going to need a bigger jet as well. I was REALLY surprised that I went down sizes. I would think that a 185 would have your belching black smoke that smells like gasoline and you would have to be changing plugs all the time!!! Maybe I got a "weird" carb or something.

All I know is that the O2 Sensor on the dyno didn't lie

NO black smoke and not a single fouled plug, but then again, my buddy is running a smaller jet then I am on his YFZ with that carb. I am also running a 52 pilot, it came off of a yz400. I am supposed to make it to the dyno soon, I will let you know.

[1fst400]

I was running a 175 with my 10.8:1 piston. but I swaped to a 12:1 and was running a tad lean.

So being the cheepo that I am I ran a drill bit throu the 175.:o . But hey it works, I guess it to be a 180 185 range.

also I think Im running a 42 pilot.