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Dual Carb Modifications
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...
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nice writeup...gave me some ideas while i still have the engine in the car lol
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nice write up dude,
but please read this thread then edit your thread accordingly
http://www.ozhonda.com/forum/showthread.php?t=5584
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Great post. Hope can hear your sound again.
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hey great write up. Just wondering if you could give an indication of any negative side effects. Fuel consumption? Also, is it possible to reverse the mods? I guess you'd need new springs? thanks
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replacing all the stock equipment and replacing the springs with new, uncut ones will return everything back to original spec... springs can be ordered from you local Honda dealer, ive done the same...
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