Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

Because that is what manufactured by hero!

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

It is dependent on manufacturer what carb he prefers . For example Hero makes two bikes Splendor and Xtreme but former uses air screw and latter uses fuel screw . Reason carb for splendor and xtreme are not same . Splendor was always said low maintainance as one can open carb and refit it flat 15 min with cleaning. It is fool proof design one cant go wrong with it . While xtreme being high revving bike wanted a carb that can provide smoother power delievery and hence CV carb was chosen . There are many other factors for selecting the carb for a particular engine by manufacturer . So in general most 4 strokers use fuel screw but not all .

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

I agree it depends on vehicle to vehicle, but what i said was as a general rule for most of our desi machines.
if i remember the afr screw is closer to the engine side (than the air filter box side).. no ? how did you confirm its a air screw ?

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Lol ok, so it doesn't perform like a FI. It's just that it is correctly tuned. I never said factory settings are always perfect/best.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

Ok i would like to jump in here. [MENTION=57344]RohIIT[/MENTION], [MENTION=53807]paul.1911[/MENTION], [MENTION=16602]s1d[/MENTION], nice explanation and all but i would also like to say something.

Usually at high altitudes air gets thinner as a result the bike doesn't get enough oxygen. The slow jet doesn't create problem as it can be made rich or lean by twist of screw. But the Main jet creates problem as not only it is big but also it sends excess fuel and bogs down the power. The stoichiometric ratio is 14.7:1, but for engine running it is 13.5:1.

What happens is that the excess fuel pumped by main jet causes the bike to bog down as enough oxygen cannot be obtained for combustion.

This problem happens more in hero bikes. Its because almost all hero bikes have larger venturis and jets than other same capacity bikes. Take the example of splendor/joy/passion and platina/dream yuga. Splendor/joy/passion runs 18 mm venturi while platina/yuga runs 16 mm venturi. Comparatively jets are bigger as splendor/passion runs 105 main jet and joy runs 100 main jet.

And yes hero bikes have better top end because of bigger venturi and bigger main jets. And yes my Joy has crossed 110 on speedo.

Even Unicorn has 115 main jet, acheiver has 118 main jet and Extreme has 128 main jet. Unicorn/acheiver uses 26 mm carb and extreme 28 mm carb.


So as venturi size increases bike needs more air. The purpose of large venturi is to feed more air. Since more air is going so bigger main jet is required. But when we go to high altitude the air density decreases and thus fuel flow increases upto a point when excess fuel hinders combustion. It is at that point that bikes bogs down and sputters.

As for passion/joy we can use 82 size main jet from pleasure, or 92 size main jet from old model splendor. Jets do not cost much and can be changed in 15 minutes.


And it is a myth that 4 strokes bikes have fuel screw and 2 strokes air screw. Splendor/passions/joy/platina/caliber/ 4S champions/ yuga and all commuter bikes use Air screw. Advantage of air screw is that it causes more precise adjustment and also idle is good.

But with the advent of CV carbs fuel screw came into existence. Fuel screws are not much responsive to tuning and also do not give as much wide range of tuning as air screw.

Slide carbs are those whose slides are connected by wire to throttle. CV carbs are those whose throttle is connected to butterfly valve and vacumn causes slide to rise.

Slide carbs are more responsive than cv carbs and also less maintenance intensive. But CV carbs have better fuel efficiency and smoother power delivery.
[MENTION=57344]RohIIT[/MENTION]- You have seen extreme throttle to be so much responsive, but you have never seen a extreme with slide carb. I have ridden an extreme with 28 mm flat slide carb and boy that thing was extremely dangerous to ride in traffic. Close the throttle in third gear and open suddenly and the front will jump.

And yes with proper tuning carbs feels as good as FI throttle response. But change the altitude or air temperature carb will fail.Only two carb were there that could function like Fi and they were solex and carter. But they became so complicated that they were ditched for FI system.


Here is a pics of solex carb and you can see how complex it is. It has a pump to give better throttle response, two butterflies, fuel enrichening system and what not. Servicing it will become nightmare.



Here is a pics of carter carb. If anyone wants to know more about this carb then ask me and i will explain in detail, but not now as it will become lengthy.


Fi meaures the air going in through a sensor in throttle body known as Mass air flow sensor. It determines the air quantity by the mass of air flowing though it. The advantage of mass air flow sensor and why it is used instead of volume air flow sensor is because mass air flow sensor can detect change in density of air which is beneficial when climate changes and also altitude.

Although a carb can be tuned to run near perfect to FI system, but a carb will fail when accelerating and decelerating.

PS- today while i was returning to home at night on highway, happened to measure the mileage of CBZ extreme after around 30 k kilometers. Bike is now at 38.6k kms, and last time i measured mileage was at 6.5k kms and after that never measured.

Mileage i got was- 80/1.4= 57.14 kpl and this is with riding at 70-80 kph at night with tuning set to slightly rich from perfect setting for better acceleration.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

[MENTION=28527]sibun[/MENTION], i would like to know more about both of these carbs pls explain in detail.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

I remember from a DIY video on Youtube that if the screw is before the butterfly then it is air screw and if it is after the butterfly then it's fuel screw..
It may not be true for all carburetors.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

@sid jee, @RohIIT jee, @sibun jee, I have clearly understood your explanations and i have no words to thank you. I wish that i could have got teachers like you in college. During my under graduate days, if i ask any general doubts to the faculty, what they use to do is, ask me a formula or an equation that i did not know, and tell me, first go and learn that, try to get good marks in all the subjects and then you will be eligible to ask such doubts! I guess they also might not have known the answer for my questions. They think that marks and grades can alone lift up the career, but according to me, studying means what i have learnt newly from this, why should i study this, what is the use of this, where can i apply this etc etc..

I asked the same question to you and the answers came flooded, thats why the embarrasment.

You all did clear my query. Let me study more about the carburetors so that i can learn too. Thank you once again for spending time and effort.

So, changing of jets into smaller size will solve the problem in higher altitudes. Am i correct?

One more thing regarding AFR mixture. I was thinking till date that perfect AFR means 50% fuel and 50% air. Only now, I have come to know that perfect mixture means 13.5:1. If the bike runs in this ratio, the spark plug will be in brick red colour as in Sibun sir's joy, right?

If FI bikes doesnt need tuning, will their spark plugs also be in that brick red colour? Next time when i visit my mechanic and happen to see any r15s or zmrs, will definitely check them

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

This reminds me , I need to clean my bike's carb - it's seen 3 years and excess of 15000 kms without any service .

While replacing clutch cable this time I took particular care to line things up correctly and grease the lever pivots and cable ends . Used some old black sodium based grease , since white lithium grease had harmed the rubber parts at the ends of the old one . On the engine end , I fitted the cable in a little different way than factory . I fitted the two adjustment nuts ( 14mm & 12mm ) on either side of the fixed-tube on the bike , unlike OE fitting like both nuts on the upper side of that tube . This also holds the clutch cable much more rigidly . Reinforced the new cable at 2 spots a) at the clip to the frame under tank b) where it bends around the T-stem . Used 14mm heat-shrink tubing for this - only 14mm would just slip over the cable end on the lever-end . Adjusted . Clutch lever is now super free and soft with exact free-play . Been riding like this for sometime and it's been a pleasure in traffic , my clutch hand is very relaxed now .

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion


Can ypu post pictures of only the cable? Or the cable ends of a stock splendour clutch cable? Will be really helpful.

Divyansh....



Ps:- sorry was out of this forum for quite some time. Mother was in hospital and all... big messed up life. but thanks to all the blessings you guys and all my friends keep giving....aaal iz well

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

How are you bro i was suspecting some kind of mishappening, good to hear that your mother is well now,may GOD provide her longer and healthier life, hope now we will see you and your advice regularly on the site.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

Yes bro, you were missing for quite a few days. Glad to know that your mother is good. Keep posting! And take good care of her.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

Thank you guys. I will.... my bike is not taken care of at all... all this running around it had gotten neglected... now time to service it clean it....will gift it new cables as well. A cousin recently bought a passion plus... reason being "xbhp has this thread I read!":thumbup:

Hero should put this up on its website as a feature! Lol!

Divyansh....

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

Though its personal choice of an individual ,why not passion xpro man, iam hearing quite a lot of praise of this xpro bike from Hero.

Re: Hero Moto Splendor/Joy/CD-Dawn/Passion

@ Divyanshp150 - hopefully everything ok now for you and your family . Sorry , my mistake was that I didn't take pics while I was fitting out the cables - I realised it later when I was writing here that I don't have any . Anyway , first just get the cables and parts from Bansal-motors . OE Hero cables are cheaper than Remson ones here . I'll guide you fully how to go about it . Just a little bit of work . Maybe you can do a small DIY about cable replacement on CD / passion / splendor here . It is such a common job we all have to do sometime - I'm just biting my fingers now for having forgotten to take pics .

How are you guys doing ? Although I was checking out this thread daily, I haven't posted or updated anything since a long time. I am trying to slowly pen it down one by one.
I must say that every member of this thread is no less than a family member. [MENTION=39856]divyansh[/MENTION]
Good to know that your mom is back home and doing well.