Dual Carb Modifications

[DualCarb]

Disclaimer: The following is provided as a GUIDE ONLY, and neither myself nor Ozhonda take any responsibility for the outcomes of someone else doing the following. You follow these steps at your own risk!


Aim: Modification of Dual Carb setups for better throttle response
Required: Screwdriver, wire-cutter, 2 performance filters for motorcycles.
Steps:1.) Remove stock airbox system and install 2 cone filters.
2.) Keihin CV carb modification
Other comments: This modification will take you half an hour to 45 mins to perform. Store all removed items for future use if you ever whish to return to stock.

I notice there are quite a few carb’d Honda owners in Australia who keep popping in asking how to get more power. The following is some information on carby modifications that I’ve posted on several other Honda forums, hoping to help the carb’d guys have some fun too. Please believe me when I tell you all these modifications together have not affected my car in a bad way, and although I have not Dynotuned my car yet, because im not done with her yet, I manage to stay hood to hood with vtecs and other “performance” models from other manufacturers.

Hopefully this can become a sticky, so that carb owners do not have to keep asking for modding tips.

I have the ZC SOHC Dual Carb in my 4G4D, with the same carb setup as you. I will give you some hints on modding those carbs, purely coz you drive a honda

First, get two motorcycle cone filters, the ones for performance bikes. Then, remove your stock airbox completely, and block off all attached piping. DO NOT block off the breather hose that goes from your valve cover to your stock airbox, get a breather filter for this one. Unbolt and remove mesh guaze covers and the spacers over carb throats. Take the two cone filters and push their rubber ends THROUGH the spacers. Bolt the spacers with filters attached, back onto carb throats, without the mesh covers. You might have to bend two little copper pipes next to throats slightly inward to accommodate the cone filters. Don't worry, they are purely for athmospherics. If you are not sure about the size filter, take a spacer, drive to your bike hop-up shop and compare sizes before buying. If you can, get filters with the rubber ends slightly larger than the hole in your spacer, to ensure a snug fit. You might have to use super-glue to make them stick... do not worry about a CAI. Carbs respond much better when they are sucking in air from 360 degrees, as opposed to from one direction only, such as a CAI. The gains from two cone-filters on the throats is much bigger than what you would gain from a CAI. Cold air is great for FI, but free breathing is GREAT for carbs...

Next, you do the Keihin CV Carb mod: You will see two silver lids on your carbs, where it says KEIHIN. Carefully remove these lids by unscrewing the screws that hold them in place. Careful not to drop any screws or dirt into the carbs once you've taken the lids off. Underneath you will see two long springs. Take out the first spring, and then cut off 2-3 coils of the spring. Repeat the process with the second spring. Next, look at the open carbs again. You will see two little plastic stoppers on top of the two pistons that the springs fit over. Mine were black, so yours might be too. Remove them.

Now, take the springs and put them back where they came out of, with the uncut ends facing DOWN. Carefully replace the carb lids.

What you've done: The springs control the rate at which the diaphragm piston valve rises when you push the accelerator. After the mod the valve rises much quicker, due to lessened spring density. This vastly improves throttle response. The plastic stoppers prevent the diaphragm valves from raising above a certain point, to keep fuel consumption lower. The higher the diaphragm raises, the bigger the needles open, the more fuel you get into your engine. The increased air from the cone filters and the fuel from the quicker lifting and higher lifting diaphragm means a cool 10-15HP increase (if you have a decently built engine already, otherwise, expect less)...

There is also the accelerator pump mod, for more throttle, and balancing the carbs is also a good idea. these mods can be found here:

http://home.netvigator.com/~bricheun/

this is an excellent site with pics on most of the mods for the dual carb setup...

I cannot seem to attach images so...In my VBGarage profile is a pic of what the two conefilters look like on my setup...

[Weq]

good advice!

[mytoycivic]

nice writeup...gave me some ideas while i still have the engine in the car lol

[ECU-MAN]

nice write up dude,

but please read this thread then edit your thread accordingly
http://www.ozhonda.com/forum/showthread.php?t=5584

[edw-R]

Great post. Hope can hear your sound again.

[wynode]

Nice post!

I've attached the image for you :)

http://www.ozhonda.com/forum/vbgarage.php?do=getimage&id=379

[Enigma]

that could just as simply be done to a single carby right?

[DualCarb]

that could just as simply be done to a single carby right?

I just gave Eclipsor some info for the single carby... the single carb is a twin barrel downdraught carb. One barrel opens on pull away, the other opens at 4500 rpm's.... ever feel a surge of power at 4500? Now you know why... the second barrel is timed to open with the torque peak of the engine...

There is a mod where you can open the second barrel permanently... any good carb service centre should be able to do it for you. You can also rejet the carb for more fuel delivery...

for more air, you can "flip the lid", like the old american monsters, where you turn the airbox lid upside down and tighten it down with the wingnut again... that way, more air is delivered to the carb, because it now breathes from 360 degrees as opposed to from one direction only with the intake pipe... which is very restrictive. Some lids do not bolt down easily when flipped, so, you have to get a flat metal plate of large enough size, trace the outline of your stock elliptical airfilter on there, cut it out, drill a hole for the wingnut, and use the new lid to tighten the filter down. That way the paper edge of the filter is exposed to open air, and will breathe from all directions, as opposed to one direction only... some aftermarket companies like www.autostyle.co.za has pancakefilters, which replaces the whole filter and lid, it just ties down with the wingnut. Or you can get the K&N replacement hi-flow filter for your car.... but still remember it will only work the way its supposed to when your carb breathes from all directions.

Oh, and thank you Wynode :)

[ed.win.]

Anyone in Melbourne that has done this mods? Willing to pay for service.

[egSi]

nice write man, some one please post more pics of this done :thumbsup:

[Kawasaki]

I might do it if\when I can get my hands on a second Dual carbi setup

[[T][L]]

did anybody done this??

[.::F[L]Y::.]

nice! can u pls post pics for each procedure??

[joyride]

Carbs respond much better when they are sucking in air from 360 degrees, as opposed to from one direction only, such as a CAI.
i dunno if this guy still posts here but i have a question. on a stock engine, would this still apply?
my reason is that on my bros civic 1.5L 12v carby motor, in the airbox there is a covering at the stock CAI. its there to distribute the airflow evenly all around the circular air filter. i have removed it and now the air only hits the filter at the entrance of the CAI.
the pro is that the air intake sounds sharper although i dont know if the car is any different. should i just put that cover back on?
i'll pics this evening if requested

[Eclipsor]

I modified the airbox on my previous car to get the effect DualCarb was talking about. Don't know if it really made any difference. Don't think it did.

I don't reackon removing that cover will do any damange. Probably still wouldn't be able to get the volume of air in as you would by flipping the lid. However, it is likely to ruin your air filter quicker as it will be sucking through one part of it instead of distributing the dirt more evenly.

[chingaling]

just wanna know what size of the bike filter did he bolt it in ? :eek:

[Eclipsor]

You mean the diameter of the joining tube? You should be able to see the carb throats if you take off the airbox lid. Should be easy enough to measure.

Since dualcarb dosn't seem to check here anymore check out this thread on dseries. http://www.d-series.org/forums/showthread.php?t=23877

This is where alot of this information orginated plus more.

[joyride]

I modified the airbox on my previous car to get the effect DualCarb was talking about. Don't know if it really made any difference. Don't think it did.

I don't reackon removing that cover will do any damange. Probably still wouldn't be able to get the volume of air in as you would by flipping the lid. However, it is likely to ruin your air filter quicker as it will be sucking through one part of it instead of distributing the dirt more evenly.thought so. that why i rotate the filter regularly :p

[rly1]

Anyone's got a picture of the cone filters ?
no idea what they look like

[chingaling]

just go autobarn and get the UNI FILTERS.. and custome ur own size ..

[rly1]

Hi Chingaling,

Is the uni air filters from autobarn (smaller CAI type) the same as the cone filters he's talking about ?
cos now, it's just stucking 2 smaller pod filters rather than one CAI with pod filter

[Eclipsor]

Just get any filter that will fit. Check the diameter of the carb throats and take that with you. Also check how much clearance you have with the firewall to work with. The original poster used motorbike filters so if you have the measurements maybe check out your nearest bike shop. See what they've got.

Here's some examples:

http://home.netvigator.com/%7Ebricheun/ram2.JPG

http://img222.imageshack.us/img222/3264/picture0032zu6.jpg

[chingaling]

Hi Chingaling,

Is the uni air filters from autobarn (smaller CAI type) the same as the cone filters he's talking about ?
cos now, it's just stucking 2 smaller pod filters rather than one CAI with pod filter


those uni filters are one peice of foam material.. and u cut it into ur own carby size.. easy to find.. the filter bit is like 8 dollars..

[chingaling]

Just get any filter that will fit. Check the diameter of the carb throats and take that with you. Also check how much clearance you have with the firewall to work with. The original poster used motorbike filters so if you have the measurements maybe check out your nearest bike shop. See what they've got.

Here's some examples:

http://home.netvigator.com/%7Ebricheun/ram2.JPG

http://img222.imageshack.us/img222/3264/picture0032zu6.jpg


where did u got those mushroom filter from ? i wanna get them ey .. they are cool . PRICE and WHERE etc :D

[Eclipsor]

Sorry. Those aren't mine. Just used the picture.

[rly1]

thanks!
I notice the 6 labelled hoses from the pics, are they the ones to block off ?
do we block them all off ? how ? with what ?

[chingaling]

block it with right size's spare screws

[Eclipsor]

thanks!
I notice the 6 labelled hoses from the pics, are they the ones to block off ?
do we block them all off ? how ? with what ?
I never got as far as doing this so I can't tell you for sure. But yeah just try blocking off all hoses that went to the airbox. Probably stick a breather filter onthe valve cover ventilation though. Like people do with cold air intake systems.

But yeah just get a screw or I think you can get vac tube terminators. Try supercheap. Or if you have spare golf tees sitting around shove one of them in and cut it off. Just whatever works.

As I found out though. None of this stuff is really an exact science. Unless you really know what you're doing you have to be prepared to experiment and trial and error until it works. Probably not the best thing to be doing on a weekday afternoon when you need the car to get to work in the morning kind of thing. There are lots of variations on the twin Keihin carbs with varying amounts of emissions equipment attached. Depending on what year you have. Generally the later the model the more complicated the carbs are because of the useless emissions stuff they kept adding on.

But it is fun. :)

[rly1]

I checked out bike shops but still couldn't find something that will fit through the spacers. I explained to the shop owner what I wanted to do and he reckons this isn't going to work unless I can tight the filter down to the throat(so it can grab onto something, something like a custom filter adapter that fits to the 2 spacers screws and out so that the actual filter can be tighten to ?)
Is this the reason why it was suggested to super glue the filter down ?
Anyone's done this in Melbourne and have an idea where I can get those damn filters. :P
I couldn't find anything useful in AUTOBARN either. :(

thanks

[Eclipsor]

Yeah they'll need to be tightened down somehow. Either by having the filter tube larger than the carb throat and jamming them on. Or the same diameter and maybe try using some of that silicone coupling pipe.

[rly1]

I was thinking of the jamming method but would that be tight enough ?
when air are sucked it, wouldn't air also flow from the side gaps(if not superglued to close down the gaps completely)

[chingaling]

I checked out bike shops but still couldn't find something that will fit through the spacers. I explained to the shop owner what I wanted to do and he reckons this isn't going to work unless I can tight the filter down to the throat(so it can grab onto something, something like a custom filter adapter that fits to the 2 spacers screws and out so that the actual filter can be tighten to ?)
Is this the reason why it was suggested to super glue the filter down ?
Anyone's done this in Melbourne and have an idea where I can get those damn filters. :P
I couldn't find anything useful in AUTOBARN either. :(

thanks

dont use GLUE .. it will melt

[Eclipsor]

Just use one of those hose clamps if you're worried. That's all that holds my intake together in a couple of places.

[rly1]

Sorry Eclipsor, I think I got lost. The ideal situation would be to use hose clamp to stick a pod filter to an intake, like what CAI people do.
The problem with the dual carby is that once I take off the lid of the air box, it's got only 2 carbs throats, there's throats are jus wholes without anything that you could clamp your filter on. You can only stick the filters necks into the spacer(then into the throat). Isn't it what this threads was saying ? or am I completely lost ?
Then, it was also instructed to chose slightly bigger filters to ensure a tight fit . So once the filter necks are pushed in, I was asking if there were still gaps and if we could close the gaps by using some super glue or if it's not required. have any of you guys done this ? can you post a pic of how the filter meets the carbs throats ?
thanks

[Eclipsor]

Have you taken the whole airbox off? Including the base? Maybe I'm picturing them wrong in my head. I think I still have a set at home. I'll have a look later on.

[chingaling]

this is what i did .. i took the arbox out.. and u will see the 2 throat with the Metal mash bit on the top. so u take the mash out and custome ur own filter size and rep around the mash and put it back in :D easy simple as that.. dont need those fansy pod filter

[rly1]

I haven't taken out the whole airbox yet,
just took out the lid, one piece of mesh and one of the spacer out to get the correct size when I go around shops.
Chingaling, are you saying that you just cut a piece of foam, stuck it on the 2 piece of mesh and stuck the mesh back on ?
That sounds good but does it shows any improvement ?

[rly1]

Chingaling, would you have any pics of your current setup ?
if so, please post

thanks

[chingaling]

Chingaling, would you have any pics of your current setup ?
if so, please post

thanks


yeh i did that.. and it actually helps coz got my air flow as well .. and plus remember to cut the springs inside the kehien piston thingy cut about 2 - 3 coils

[rly1]

Chingaling, Have you got any pics ? because I wanna see how you got around the whole in the mesh (it is for one of the vacuum tubes)
did you remove the piece with the metal tubes out (right between the 2 carbs throats) ?
thanks

[rly1]

Chingaling, Ignore my last post. The metal tube sticks out from the throats, through the spacers and through the mesh, can you show me how you did your setup to accomodate that metal tube ?
thanks

[chingaling]

Chingaling, Ignore my last post. The metal tube sticks out from the throats, through the spacers and through the mesh, can you show me how you did your setup to accomodate that metal tube ?
thanks

alright i will take a pic after my assignement :P

[rly1]

thanks, I'll be waiting for your pic

[rly1]

Chingaling, any updates for the pics ?
thanks

[chingaling]

sorry its not clear at all.. but u see the filter right below the BIG TORCH ? thats the one im talking about

[rly1]

Thanks Chingaling, I get the idea but I'm just worried that the piece of foam might get sucked in if it's not attached properly.
did you use any glue or anything ?

[chingaling]

Thanks Chingaling, I get the idea but I'm just worried that the piece of foam might get sucked in if it's not attached properly.
did you use any glue or anything ?

it wont bro.. the foam is sitting on the top of the MASH bit.. so it wont go in.. and CARBY dont suck air that strong.. so is ok ;)

[89civic]

it wont bro.. the foam is sitting on the top of the MASH bit.. so it wont go in.. and CARBY dont suck air that strong.. so is ok ;)

hey. did u just get the unifilter foam covers and make your own size? did u put it between the spacer and the gold metal cover? did it make improvements? and do u suck to much hot air in? i went up the street with no filterbox lid with no filter and it didnt make a difference

[chingaling]

hey. did u just get the unifilter foam covers and make your own size? did u put it between the spacer and the gold metal cover? did it make improvements? and do u suck to much hot air in? i went up the street with no filterbox lid with no filter and it didnt make a difference

it really depends how much air u got in side the engine bay .. to really make improvment u need some Customer air Induction.. to bring the air in .. it make difference in mid range especailly Mt run .. coz it always kept in high rev.. it response a bit quciker for my car ;)

[Jord]

worth doing u think guys?

[89civic]

worth doing u think guys?

i dont reckon, my car goes better with the k&n pod behind the light with a heat shield

[Eclipsor]

worth doing u think guys?

Not sure about just getting rid of the air box. But doing the whole lot. Including chopping the springs etc has been fairly well proven over on dseries.org

[89civic]

how many springs did u guys cut? i cut 2 and the exhaust crackles heaps when slowing down

[rly1]

worth doing u think guys?

I had the normal CAI setup with a heat shield on mine for ages until I bumped into this thread. So was thinking to give it a try since it claims that CAI is no much use for carby but I'm finding it damn hard to get that filter thingy attached down here in melbourne.

89civic, you know where I can get those universal foam filter down here in melbourne ?

thanks

[rly1]

it really depends how much air u got in side the engine bay .. to really make improvment u need some Customer air Induction.. to bring the air in .. it make difference in mid range especailly Mt run .. coz it always kept in high rev.. it response a bit quciker for my car ;)
On this topic, I saw the thick induction tube in your picture. I wanted to know where the tube sucks the cold air from ? I initially wanted to do this too but couldn't find anywhere in my engine bay/bumper to lead the outside air onto the air filter so I settled with some vaccum tubes :P

[chingaling]

On this topic, I saw the thick induction tube in your picture. I wanted to know where the tube sucks the cold air from ? I initially wanted to do this too but couldn't find anywhere in my engine bay/bumper to lead the outside air onto the air filter so I settled with some vaccum tubes :P

just drew a whole in the bumper take the OEM CAI pipe out, and den just wat eva u like to link it into it..

[89civic]

rly1, autobarn have the foam filter things that go on webbers or something.not sure if they will work the way i think they will though

[rly1]

thx 89civic but which autobarn u talking about ? I think they don't store the exact range of product in each store, the one in doncaster does not seem to have anything else than pod filters(CAI type), I've asked them.

thanks

[89civic]

thx 89civic but which autobarn u talking about ? I think they don't store the exact range of product in each store, the one in doncaster does not seem to have anything else than pod filters(CAI type), I've asked them.

thanks

ahhh righto. the one in frankston has them, they have heaps of filters, for carbs, injected, rally purpose filters. the rally ones are what i was talking about, they look like a sock or something that goes onto something else. not sure how they work exactly

[rly1]

thanks 89civic, I'll check it out sometime, is it the one on
Shop 7, 30 McMahons Road, Frankston VIC 3199 ?

thanks

[89civic]

thanks 89civic, I'll check it out sometime, is it the one on
Shop 7, 30 McMahons Road, Frankston VIC 3199 ?

thanks


yeh thats the one, might pay to give em a ring first, save u traveling down and not get what u want. let me know how it goes :)

[rly1]

Thansk 89civic, I was around the area last saturday and drop by.
I found something like a round piece of foam(like a disc) that I will cut to fit in between the spacers and the mesh.

thanks

[89civic]

Thansk 89civic, I was around the area last saturday and drop by.
I found something like a round piece of foam(like a disc) that I will cut to fit in between the spacers and the mesh.

thanks

ok good one, i was thinking of doin this. let me know how it goes! if it goes alright i might do it to, i have a k&n pod on the end of the intake pipe and took the filter out of the air box.

ps: how much was the foam?

[rly1]

Yeah, I have the exact same current setup, will let you know how I go.
the foam was $12

[rly1]

Just got the setup done yesterday. Not sure if it makes a big difference but the intake is surely louder, I can hear it sucking air while driving lol
going to leave it on for a while before going further with the spring cut

[rly1]

Now, I've had the current setup in my car for a few weeks now. Not sure if it's psycholigical thing but I don't feel the car being at all faster. I even feel it might be slower than what I had. The problem is that now, at full throttle, the noise of the air sucking is very loud, louder than the acceleration. When I had my CAI on, you can tell that when it groans! the speed was getting faster where as now, the air is being sucked but the acceleration doesn't match the noise output. Anyone feels the same ?

[chingaling]

take a pic and show what was ur previous set up and current set up .. qanna see

[rly1]

old setup is simply a CAI, metal tube from air box linked to a pod filter with heat shield.
new setup is remove all the above, air box still there, remove the cover at the back and placed two filter element between mesh and spacers.

[silver_screen]

well i cut the springs 2day and did all that is said in the first post...

very good, noticable response difference and much better top end power

[SeverAMV]

sorry to bring back an old thread and i'm probably asking a stupid question, but has anyone tried the setup listed on the first post of this thread except with the intake hose still in position, as well as a bonnet scoop?

[Jums]

Now, I've had the current setup in my car for a few weeks now. Not sure if it's psycholigical thing but I don't feel the car being at all faster. I even feel it might be slower than what I had. The problem is that now, at full throttle, the noise of the air sucking is very loud, louder than the acceleration. When I had my CAI on, you can tell that when it groans! the speed was getting faster where as now, the air is being sucked but the acceleration doesn't match the noise output. Anyone feels the same ?

try tuning or get bigger jets. with all the air it's sucking in it might be hungry for fuel.

[trism]

that post is nearly 2 years old

learn to check the dates

[SeverAMV]

hmm, random post, but for those who are running high comp domed pistons with the keihin dual carbs, you may notice that the fuel mixture doesnt spark as easily and you cant advance ignition timing far enough (domed pistons swirl the mixture, which hinders the spread of the flamefront).

refer to http://onecamonly.com/showthread.php?goto=newpost&t=447 for info on how you can modify factory dizzy to allow for more advance.

oh and @Jums, if it feels less powerful with said mods, then its more likely to be running rich rather than lean. dull acceleration is a characteristic more associated with running rich, lean is normally better acceleration (considering on a stocker, the keihins have an AFR of around 11.8:1).

[Davo "90 civic"]

ok so just read over the first few pages. so we should block off the hoses running to the stock box, yes?. what are these?. what effects will it have to block them off?. and i know to leave the one that goes to the.