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By Allanfox
#86482
Hi, question if I may?

On my 2008 Electra X is there any advantage in removing the PAV and associated piping, airbox etc but keeping the original CV carb but with a K&N type filter, is the carb sufficiently tune-able to be adjusted to the new situation and would this add to overall performance? I have read the Matthew Morrow article hosted in out hosts technical section. Just curious if anyone has done this?
User avatar
By Adrian
#86485
A lot of Electra-X owners would have junked the PAV system from new, just remember to blank off the air feed into the cylinder head exhaust port and the little brass pipe feed in the carb mounting rubber. It's not really a performance thing, just getting rid of some extra gubbins needed to get these bikes through the then-current Euro 2 emissions regulations.

The CV Mikarb is tunable to an extent, I can post some details, though for better performance you probably need to fit one of our hosts' free-flowing exhaust pipes as well as a less restrictive silencer and maybe raid the after-market for one of any number of different zoomy carbs available. Fitting a 17T gearbox sprocket helps a lot with general zippiness (is that a word? It is now), and for serious top end, a set of cams from an old Redditch Bullet helps considerably.

Mikuni TM36-61 carb shown fitted.

A.
DSCN3708.JPG
User avatar
By Allanfox
#86490
ok thanks, think ultimately an Amal conversion but was just curious what I could do with what I have, would like to read your CV tuning post?
User avatar
By Allanfox
#86491
ok thanks, think ultimately an Amal conversion but was just curious what I could do with what I have, would like to read your CV tuning post?
User avatar
By Adrian
#86492
This was posted on another forum some years ago by someoene who experimented with the CV carb
Ric's CV Mikarb 29mm Tuning plus Slide Modification

There has been a lot of activity recently on various other sites with regards to tuning the Electra X lean burn 500 but without incuring the expense of a larger carb.
As a lot of this info has been compiled here over the last year or so among some postings not accessible to casual browsers, I thought I'd rehash the basics of what worked for me (before I went and spent a lot of money on a larger carb). Some info has been obtained from other sites, some of it no longer here as the posts have been cleaned during 'housekeeping'

Feel free to add your own improvements

The original idea of experimentation was to improve mid range performance , not top end performance, although I did end up with both. MPG has improved as this set up is a lot less restrictive than stock, but realistically the additional MPG obtained will never be recovered against the costs incurred, but it nicer to be able to stretch that distance between fill-ups.

The Electra 29mm CV carb can still work fairly effectively on the bike providing its acompanied with a few other changes.

The standard filter needs to be changed for its direct K&N replacement, the
DU-0100, this will fit straight into the air box. The eliptical/circular hole in the baffle plates inside the box need to be opened up to allow a better flow of air inside the chamber. Remove a 2mm wide strip from each half of the box.

Replace the standard downpipe with a Hitchcocks unrestricted one.

Replace the standard silencer with a free flow unit.

Adjust the carb mixture screw to around 4 turns out.

Raise the needle up one notch to its highest position.

Remove 0.8mm from the base of the slide - it may require a little more but this was the point at which mine seemed better than stock.

Increase the main jet from 110 to 120. This was the largest size I found was needed on my bike when running a straight through exhaust. 117.5 may work as well if using a slightly restricted set up.

A couple of hours of porting work to clean up the casting imperfections, (especially the exhaust)

BR9EIX Iridium plug
There is also a separate modification to the carb slide discovered by our Indian friends
Crisp Punch: Ported throttle slide on a CV Carb with a first hand review
by Jay Prashanthon May 5, 20103 Comments

Ported CV Carb Throttle Slide vs Stock CV Carb Throttle Slide
modified caeb slide.jpg
Linearity was nice on the school bus you used to go to school in, but linearity on a motorcycle this side of the economuters can mean only one thing, boredom. I’m not suggesting liter class SBKs or ported two strokers for your daily dose of gonad juices here, I’m talking about how your daily ride 150cc motorcycle can put a smile on your face every time you whack open the throttle. Kicking off this tech post, I’m going to elaborate and review a simple mod on the CV(constant velocity) carburetor that can make your everyday commute just that tad bit exciting.

Let’s begin with understanding how CV carbs work, in a layman’s perspective, and why your engine doesn’t die out as you whack open the throttle on your 150cc Pulsar/Karizma or Unicorn. First of all, you need to remember that the advent of the CV carbs was simply to make the riding experience simpler and kinder by giving the carburetor more control than your right fist. It is therefore of no surprise that the dirt bike crowd simply shun the sluggish CV carbs for ultra responsive flat slides. The CV carb basically works by it’s slide operating on differences in vacuum created by the engine’s piston, instead of being connected directly to the throttle cable.

This is in complete contrast to round slide and flat slide carburetors, whose slides are connected directly to the throttle cable thus responding instantly to the throttle inputs your right fist gives it. The CV, on the other hand has a diaphragm atop it’s throttle slide that will regulate the speed/rate at which the throttle opens or closes. This, it does by gradually regulating the vacuum inside the carburetor and thus the movement of the slide. Hence, you can whack open the throttle on a CV carb throttle and still manage not to cause the engine to starve, which otherwise would have been the case if you did the same with a round/flatslide carb.

CV Carb Cutaway

Coming to the throttle slide on a CV carb, there usually are two or three ports/holes/orifices on the bottom of the throttle slide. On of these holes, the one which is in the center, accommodates the needle of the carburetor. The other hole(s) are basically vacuum ports, which are extremely important as they are the ports which are responsible for vacuum changes, and hence directly impact the working of the CV carb. The throttle slide modification in question is directly related to these ports.

What we essentially do in this modification, is we drill out the vacuum ports to a slightly larger diameter. For example, the vacuum ports on the Mikuni BS29 CV carb measures 1/16th of a inch in diameter. What we do is, we drill out the vacuum ports to 1/8th of an inch, effectively doubling it’s diameter. This doubling of diameter increases the flow of air through these ports by 4 times. Thus, when you whack open the throttle of a motorcycle that has a ported throttle slide in it, this time, the rate of change in vacuum will be a lot quicker than that in the stock slide. As this rate of change in vacuum is quicker, your throttle response goes up massively and your motorcycle feels much more livelier. Of course, you won’t be going any faster but you’re motorcycle will certainly feel a lot more agile and more responsive to your throttle inputs.

Chinmay Dangre or CorePower Motorcycles sent me a ported throttle slide which I fitted on my Stage 1 Royal Enfield Bullet Machismo LB500 last Sunday. Riding down the Airport road in suburban Bangalore, I immediately felt a marked difference in the way my Bullet responded to throttle inputs. As I run on a richer pilot mixture to prevent popping from my goldstar muffler, my initial throttle response is usually sluggish/lumpy on the stock CV carb. But with the ported throttle slide in my carb, the initial throttle response became a lot more smoother and more controllable. I could literally control the throttle down to the last mm of it’s play, which was hitherto an impossibility on the more sluggish stock CV carb.

Since my motorcycle runs on a free flow intake and exhaust, I have ample low end torque. This ported throttle slide has enabled me to control and use this torque more efficiently. With the ported throttle slide, I can now ride the torque curve for say till the first 1/4th of the throttle opening, like say on a STD350 and thump along nicely, and that is quite a statement to make. Once I whacked open the throttle beyond the initial 1/4th throttle, my bullet simply lurched forward, quite unlike the measured, linear way in which it used to gather speed before. All in all, my Bullet now feels a lot more lively and I’m enjoying the improved throttle response to the hilt.

For people interested in porting their throttle slides to make their bikes more responsive, you can do so by
1> Drilling out your existing throttle slide. This requires a very steady drilling hand as it is extremely easy to burr the slide and thus destroy the vacuum ports beyond repair. Also, care must be taken to make sure that you handle the diaphragm atop the slide very gently as the extremely delicate diaphragm is prone to tearing if mishandled.
2> Contact Chinmay Dangre at macasp@gmail.com and specify your motorcycle model. Chinmay will then port a new throttle slide and ship it over to you. Then, you can ask your mechanic to do the install of the ported throttle slide or if you’re a DIYer, you can do it yourself if you’re confident of your way around carburetors. For people in Pune, the fitment can be done at Chinmay Dangre’s workshop. For pricing details, please contact Chinmay directly.

This mod will work on all motorcycles that run on CV Carbs, and these include, but are not limited to, Yamaha Gladiator/Fazer/FZ16, all Bajaj Pulsars including the Pulsar 135, Bajaj Discover 125 and 135, Honda Unicorn, Suzuki GS150R, Hero Honda CBZ Extreme, Karizma, all Royal Enfield Bullet UCEs exceot the Classic 500, Royal Enfield Thunderbird LB350 and Royal Enfield Machismo LB500.
Hope this helps.

A.
User avatar
By Allanfox
#86496
Haha, understood! Many thanks makes interesting reading and will greatly help in my very fundamental understanding of CV carbs, not looking for a race bike but if I can improve overall running and throttle response etc then worth doing!

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