Flat slide carbs with air box - do you have to have the ram air?

[neil_cb125t]

hey peoples - calling those who have GOOD experience with FCR carbs and airboxes.

I have my FCRs fueling purfectly with a simple tray creating an air casim under the tank. There is only the 2 holes on the top of the tank to let air in. ( ZXR400)

I also have a Ram air box that bolts onto the head between the carbs, thou when i run the box.....
A) i could not get it to tune properly ( but will go to the dyno for this )
B) The Ram air means i have to move the Radiator lower, which means the cooling fan HAS to come off. I would rather not rermove the cooling fan particulary during events such as Wangas.

So if i put the airbox on but have NO ram air will i still gain a benefit? ( from my tray setup ) Or will the 33mm FCR swallow all the air in the box and then starve out??

cheers

chappy

[Sidewinder]

hey peoples - calling those who have GOOD experience with FCR carbs and airboxes.

I have my FCRs fueling purfectly with a simple tray creating an air casim under the tank. There is only the 2 holes on the top of the tank to let air in. ( ZXR400)

I also have a Ram air box that bolts onto the head between the carbs, thou when i run the box.....
A) i could not get it to tune properly ( but will go to the dyno for this )
B) The Ram air means i have to move the Radiator lower, which means the cooling fan HAS to come off. I would rather not rermove the cooling fan particulary during events such as Wangas.

So if i put the airbox on but have NO ram air will i still gain a benefit? ( from my tray setup ) Or will the 33mm FCR swallow all the air in the box and then starve out??

cheers

chappy

it has ran air?
arnt they just blanked off?

[WarrenW]

Neil, I have a copy of the F3 factory kit manual for the axr and they run FCR carbs with effectively a heat seperator plate above the motor only. Granted yours will suck in much more air due to the 450 kit, but it should be quite adequate. Yes you WOULD benefit from the ram air at approx 100mph onwards, I just dont see that happening too often at Wangas.

If you want a copy of the manual PM me and I will send it - it's largish in size.

Cheers
W.

[slowpoke]

Haven't got experience with FCR's but my old carb'd R1 had an after market ram air box fitted. Amongst the R1 forums there was a fair bit of talk about ram air boxes and the difficulty in tuning the carbs, mostly resulting from the carbs sitting in ambient air but with pressurised air flowing through them, which screws up the fuel metering as your speed increases. From memory the trick is to either have the ram air box enclose the carbs or have the breathers from the carbs venting to the pressurised air box. The pressure in the float bowls/carbs has to match the pressure in the airbox.

Sorry I didn't read up too much on the latter as my carbs were enclosed in the air box and everything balanced out. In it's last incarnation (cams, headwork, compression etc) and on Welly M/C's dyno it made the same hp as a K5/6 GSXR1000 with PC111 and slip on...and at 12k rather than 13.5k. It fuelled perfectly and was as happy dawdling through traffic as it was at a track/race day.

Good thinking with the cooling fan. I nearly got caught out with my CBR at Wanganui when someone crashed on the warm up lap and we were held for ages on the grid. With no starter fitted I couldn't turn the bugger off, so it was a nervous few minutes.

[neil_cb125t]

Haven't got experience with FCR's but my old carb'd R1 had an after market ram air box fitted. Amongst the R1 forums there was a fair bit of talk about ram air boxes and the difficulty in tuning the carbs, mostly resulting from the carbs sitting in ambient air but with pressurised air flowing through them, which screws up the fuel metering as your speed increases. From memory the trick is to either have the ram air box enclose the carbs or have the breathers from the carbs venting to the pressurised air box. The pressure in the float bowls/carbs has to match the pressure in the airbox.

Sorry I didn't read up too much on the latter as my carbs were enclosed in the air box and everything balanced out. In it's last incarnation (cams, headwork, compression etc) and on Welly M/C's dyno it made the same hp as a K5/6 GSXR1000 with PC111 and slip on...and at 12k rather than 13.5k. It fuelled perfectly and was as happy dawdling through traffic as it was at a track/race day.

Good thinking with the cooling fan. I nearly got caught out with my CBR at Wanganui when someone crashed on the warm up lap and we were held for ages on the grid. With no starter fitted I couldn't turn the bugger off, so it was a nervous few minutes.


Cheers matey - my box will fully enclose the carbs - it may be a trip to mr DYNO

[neil_cb125t]

Neil, I have a copy of the F3 factory kit manual for the axr and they run FCR carbs with effectively a heat seperator plate above the motor only. Granted yours will suck in much more air due to the 450 kit, but it should be quite adequate. Yes you WOULD benefit from the ram air at approx 100mph onwards, I just dont see that happening too often at Wangas.

If you want a copy of the manual PM me and I will send it - it's largish in size.

Cheers
W.

CHeers warren - yes i pretty have what the Kit states that tray thingy. the ram air would be good - i noticed it changed the power delivery HUGELY when it was on... very smooth it felt like the CVs were back on. but was wheel standing in 2nd....... I just think that having an air box is better than open carbs - particulary as my lack of airflow going under my tank.

i may be off to the dyno to get it right

[mossy1200]

I just ordered vstack twin pod snouts for mine Neil as the suck is the most important aspect.I would recommend you make every effort to stop the hot air rising of engine.Adapting your intake snouts to provide a cold air baffle block to prevent the hot air coming up and then letting the carbs draw its own air(cooler )may gain more than trying to ram them.
If you do go ram air then make sure they run the jet size a jet to rich on the dyno.
I spent time and about $20 buying roofing patch foil which I installed onto base of tank to keep the fuel temp low.Go down to you local fire station and get them to donate you an old firemans jacket and wrap those carb bases.
Cool fuel will give you a couple of cheep hp.

[neil_cb125t]

I just ordered vstack twin pod snouts for mine Neil as the suck is the most important aspect.I would recommend you make every effort to stop the hot air rising of engine.Adapting your intake snouts to provide a cold air baffle block to prevent the hot air coming up and then letting the carbs draw its own air(cooler )may gain more than trying to ram them.
If you do go ram air then make sure they run the jet size a jet to rich on the dyno.
I spent time and about $20 buying roofing patch foil which I installed onto base of tank to keep the fuel temp low.Go down to you local fire station and get them to donate you an old firemans jacket and wrap those carb bases.
Cool fuel will give you a couple of cheep hp.


thats pretty much what i have now... a tray under the carbs and over the motor with HEAT SHEILD on it trying to keep everything cool. There just is no physical way that air comes in..... ive also been told that an airbox is better than open carbs... every new race bike has an airbox.. every old bike with carbs in WSB had an airbox....

i got one for free.. so will give it a go aye!!

hows your rebuild goin?

[bistard]

Go to the dyno young man!!

[roadracingoldfart]

Go to the dyno young man!!


Bin thinkin bout that ....... :eek5: Will the dyno fans create enough false airflow to replicate the track ???

[bistard]

Bin thinkin bout that ....... :eek5: Will the dyno fans create enough false airflow to replicate the track ???

It does not need to,providing you get the carbs set up & are enclosed in the new airbox,the carbs are equally pressurised then it is all good from there