Street Fighters For the unconventional CBR builder.

F2 Running Lean with no fairings

  #1  
Old 03-29-2013, 10:30 AM
Senior Member
Thread Starter
Join Date: May 2012
Posts: 136
Default F2 Running Lean with no fairings

What do you guys do about this? I routed the carb vents to a tee and inserted that into the underside of the airbox. That didn't work so someone on customfighters suggested inserting the two vents individually. He's been very helpful and seems to know what he's talking about so I think his idea should work but I want to know what others think. I won't be able to try it out for a month so I'm left thinking about it until then.

Here's a pic of it for kicks
 
  #2  
Old 03-29-2013, 06:54 PM
Conrice's Avatar
Retired Super Moderator and Fighterer
Join Date: Nov 2006
Posts: 6,148
Default

i find it hard to believe you had a noticeable a/f mixture change by taking off the fairings....what makes you think you're running lean? and as far as the vent tubes.... i haven't messed with f2/f3 carbs in a long while. i was looking at some other pictures on-line - don't the vent tubes run to some sort of valve or box looking thing? and then they go up to the front of the box by the air tubes that lead into the airbox?

have you messed with your pilot screws at all?
 

Last edited by Conrice; 03-29-2013 at 07:08 PM.
  #3  
Old 03-30-2013, 09:47 PM
Senior Member
Thread Starter
Join Date: May 2012
Posts: 136
Default

Originally Posted by Conrice View Post
i find it hard to believe you had a noticeable a/f mixture change by taking off the fairings....what makes you think you're running lean? and as far as the vent tubes.... i haven't messed with f2/f3 carbs in a long while. i was looking at some other pictures on-line - don't the vent tubes run to some sort of valve or box looking thing? and then they go up to the front of the box by the air tubes that lead into the airbox?

have you messed with your pilot screws at all?
Originally Posted by Mustapha dump View Post
The main cause of issues when the fairings are removed is the float chambers seeing a slightly lower pressure than the airbox sees when moving at speeds above 45mph or so.
The ZX series of Kawasaki sportsbikes suffer from this problem very acutely.
What you really need to do rather than restricting the amount of air entering the airbox, is to enable the float chamers to see the same pressure reference as the airbox.
The easiest way to accomplish this is to find the two Tee pieces between carbs 1&2 and carbs 3&4 which are the float chamber vents, on some banks of carbs on the Hondas it is one large Tee piece between the 2&3 carbs as all 4 carbs are linked across the top.
Once you have determined the float chamber vents, attatch a short length of rubber hose to the Tee piece, and then run it into the airbox through a hole drilled in the underside just large enough to pass the hose through tightly.
Face the open end of the hose towards the front of the bike under the airfilter, if needs be slash cut the hose at 45 degrees and face the cut upwards and forwards.
By doing this the float chamber vent will be fed by the air entering the airbox which then ensures that the pressure in the float chambers is equalised with the airbox pressure, once this is achieved the air passing through the venturi will suffer a slight pressure drop, as this happens the air pressure in the float chamber becomes slightly higher than that in the venturi directly above the needle jet/jet needle, and this higher pressure in the bowl then forces the fuel up the needle jet/emulsion tube and introduces it to the airflow through the venturi where it is then atomised and carried into the cylinder.
I've had to sort out quite a few "Ramair" issues on sportsbikes that have had the fairings removed over the years, in the past the issues have been difficult to detect as they don't generally manifest when I have the bikes on my dyno, although I now have a dedicated ducted fan which I use to blow air into the airbox intakes in an effort to replicate the problem as it occurs on the road rather than me going out and testing the bike on the road myself which isn't always a practicable option when it is pissing down with rain, or during the summer when the local roads are crowded with tourists heading towards the coast.
ram air effect on cbr f1 - Custom Fighters - Custom Streetfighter Motorcycle Forum

I don't know about the f3s but on my f2 the vent tubes don't attach to anything. I have not messed with the pilot screws, maybe I should. Heres what happens: it'll freely rev to 11k (highest I tried) but under load will hesitate and cutout and 7k or so. I don't know what other explanation then its leaning out. It has a stock air filter, those intake tubes at the front of the airbox and some mystery full length can so it shouldn't be getting lean.
 
  #4  
Old 03-30-2013, 10:05 PM
Conrice's Avatar
Retired Super Moderator and Fighterer
Join Date: Nov 2006
Posts: 6,148
Default

mustapha knows his stuff....



but i just don't see how anything changes. your carbs get air from the airbox - and that hasn't changed.



pictures of your carbs would help so i can see what's going on. i remember what the vent tubes look like - they're 5/16 openings or so in between the carbs right? where are they going right now?

barometric pressure is barometric pressure. i don't see how no fairings could create a substantial difference - regardless. AND you're not the first f2/f3 streetfighter - and i haven't heard of this problem before. look at fathead's f3 fighter build or knifemaker's f2 build on CF. they're completely naked bikes - and i don't remember any mods they had to make in order for their bikes to run

but then again, even with a can and a filter (which you say is stock), it shouldn't cause that to happen...

pics would help...
 
  #5  
Old 03-30-2013, 10:38 PM
Senior Member
Thread Starter
Join Date: May 2012
Posts: 136
Default

Originally Posted by Conrice View Post
but i just don't see how anything changes. your carbs get air from the airbox - and that hasn't changed.
Supposedly at higher speeds the "ram air" effect happens, a bunch of f2 owners on customfighters had the same thing happen on their bikes. They did the airbox/vent tube mod which fixed their problems

Originally Posted by Conrice View Post
pictures of your carbs would help so i can see what's going on. i remember what the vent tubes look like - they're 5/16 openings or so in between the carbs right? where are they going right now?


Here is the tee sticking up into the air box


Top view


Originally Posted by Conrice View Post
barometric pressure is barometric pressure. i don't see how no fairings could create a substantial difference - regardless. AND you're not the first f2/f3 streetfighter - and i haven't heard of this problem before. look at fathead's f3 fighter build or knifemaker's f2 build on CF. they're completely naked bikes - and i don't remember any mods they had to make in order for their bikes to run
A bunch of people on customfighters had the same problems. f3's have different vent routing that connect to the ramair setup and serve the same purpose past 15mph as the routing under the airbox

1998 Honda CBR 600 F3 partsfiche
HUUUGE flat spot, F3 Carbs - Honda Motorcycles - FireBlades.org

Thanks for the input, hopefully I'll get this figured out
 
  #6  
Old 03-31-2013, 08:02 AM
Conrice's Avatar
Retired Super Moderator and Fighterer
Join Date: Nov 2006
Posts: 6,148
Default

well, if there have been a lot of people out there complaining about it - i'd say you've figured it out then. go ahead and do that mod that mustapha mentioned and see if it works. it seems like your little t would work, but i'd go ahead and trying doing two separate tubes in there
 
  #7  
Old 03-31-2013, 11:24 AM
Senior Member
Thread Starter
Join Date: May 2012
Posts: 136
Default

Originally Posted by Conrice View Post
...seems like your little t would work, but i'd go ahead and trying doing two separate tubes in there
That's what I thought too, which is why I'm confused on the matter . I have about a month left until I get to work on the bike again but I'll try it with both tubes and stick them in further/slash cut them at a 45 angle to open them up more as mustapha suggested
 
  #8  
Old 04-11-2013, 07:23 PM
Member
Join Date: Feb 2012
Posts: 83
Default

I vented the carbs to the airbox via a T and it took car of the 'ram air' effect. but it was still running lean at full throttle. I changed main jets to 138k and it's pulling all the way through the rpm band....what size is your main jet?
 
  #9  
Old 04-20-2013, 12:23 AM
Junior Member
Join Date: Apr 2013
Posts: 8
Default

Have you been reading your plugs?
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
dafizuck
General Tech
4
11-20-2014 07:32 AM
stealthy92
General Tech
2
09-21-2012 12:34 PM
cbrpaul
How To's
3
08-17-2010 07:58 AM
plastikmelter
General Tech
5
06-18-2006 03:13 PM
reggies35
CBR 1000F "Hurricane"
3
06-14-2006 10:20 PM


Thread Tools
Search this Thread
Quick Reply: F2 Running Lean with no fairings


Advertising
Featured Sponsors
Vendor Directory

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.