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Old 07-09-2010, 03:17 AM   #1
echazar
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Exclamation About my Haojue 125cc Motorcycle

Hi everyone, I am from Mauritius, an island in the Indian Ocean. Here we have chinese motorcycle and I do possess one whose make is Haojue and it is 125cc. It is a four stroke motorcycle.

However I have modified it by changing my cylinder to a 150cc, I have also changed my carburetor which is now a Keihin one. I have put sprocket 17*35 sprocket.

The problem is that my bike is very slow at start. That is it has a very poor acceleration. Another problem is when I goes uphill I have to changed gear. Moreover, when it is in slope I have much speed but the problem is that I ride almost everytime on the 4th gear.

Can anyone help me so that I can get a good acceleration and a good speed too. If there are other modifications that I can do too...

Please note that the original sprocket is 15*39 sprocket.

Thank you
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Old 07-09-2010, 10:11 AM   #2
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Welcome to the forum. I am sorry that I can not help you with your bike issue. I know less than nothing about Chinese bikes.
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Old 07-09-2010, 12:08 PM   #3
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You went the wrong way with the sprocket change. You added top speed with the 17*35 at the expense of acceleration. If you changed to something like 17*41 you would gain acceleration at the expense of top speed.
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Old 07-09-2010, 02:52 PM   #4
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Welcome to the forum.
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Old 07-09-2010, 04:41 PM   #5
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Welcome to the forum...
The reason you have poor acceleration is the you changed your gearing from 2.6:1 down to 2.0:1...
This is good if you want to cruise at lower rpm but it will give you poor acceleration...
If you wanted better acceleration you should have changed your gearing to something like 15:42 and this would drop you ratio to 2.8:1. ...

Oh, I just looked and joncallihan said the same... Teach me to read all the posts... LOL...
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Old 07-12-2010, 10:39 AM   #6
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Default Sprocket Change

Hi, everyone thank you for replying to me. I would change the sprockets and see what effects it has and I will inform you.

By the way soxOZ can you explain me a little bit about the gearing ratio you are talking plz. The 2.6.1 down to 2.0.1 and etc... can you explain how you get this and calculate.

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Old 07-12-2010, 12:08 PM   #7
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Just divide rear teeth by front teeth...

Example: 35/17 = 2.0 or 39/15 = 2.6

So in the first example of 35/17 that means your ratio is 2.0:1 which means the front sprocket will have to turn 2.0 revolutions for every 1 revolution of the rear.

The second example of 39/15 means that your ratio is 2.6:1 which means the front sprocket will have to turn 2.6 revolutions for every 1 revolution of the rear.

As the ratio goes down, acceleration goes up, and top end goes down
As the ratio goes up, acceleration goes down, and top end goes up

Also you have to remember that changing sprockets cannot and will not ever change Horsepower. So you will always have the same amount of horsepower unless you get a larger engine. All the sprocket changes do is allow you to manage how that power is applied.
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Old 07-12-2010, 12:17 PM   #8
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Calculate final drive ratio by dividing number of teeth on rear wheel sprocket by number of teeth on counter shaft sprocket.

Original was 39 (rear wheel) / 15 (counter shaft) = 2.0 : 1

The result is for each 2.0 revolutions of the counter shaft, the rear wheel goes around once.

Changed was 35 / 17 = 2.6 : 1

The result is for each 2.6 revolutions of the counter shaft, the rear wheel goes around once.

If there are no other changes, the lower the final drive ratio, the better the acceleration. What you have done should provide better top speed at the expense of acceleration. If you had added teeth to the rear wheel or taken teeth off the counter shaft, you would have added acceleration at the expense of top speed. You can't have both with out increasing the available power.

Jon

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Old 07-12-2010, 02:48 PM   #9
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Ok I did understand the concept. Thank you very much. Does somebody knows if there is an optimal drive ratio?

Moreover does modifying or changing exhaust pipe brings more power to a motorcycle.

Furthermore what modifications can be done to a 4-stroke motorcycle?
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Old 07-12-2010, 05:49 PM   #10
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Yes, you can get a HP boost from an exhaust pipe change, but most of the time the swap requires additional work to the bike, such as shimming the needles, or re-jetting the carb (which in my opinion has more to do with the resulting HP boost than the can hanging off the back, despite what the exhaust manufacturers tell you)

As far as optimal drive ratio...it really depends on what you are trying to do with the bike. If you want fuel economy and to drop the RPM's required to maintain cruising speeds then you go up in ratio. So basically what this does is if your bike is running 5000rpm at cruising speeds...after the change it might be running 4500rpm at cruising speeds.

If you want wheelie popping acceleration, and dont really care about fuel economy or cruising speeds, then you go down in ratio. Just keep in mind that if you go this route, when you get to cruising speeds, it will probably be tapped out on RPM's and power.
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Old 07-14-2010, 02:26 AM   #11
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Bdavison could you explain me about re-jetting the carb and shimming the needles because I have only a brief idea about it. Could you also explain how it can be done and if I need an expert to do it or I can do it myself.

I am sorry if I don't understand some english terms too much as we rarely spoke english in everyday life but instead we talk in "creole".

Thank you for your comprehension.
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Old 07-14-2010, 10:38 AM   #12
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Shimming the needles is a pretty simple process.
Basically you remove the tops of the carbs, take out the diaphragm and the slide. Then you put washers under the needle to raise it up. The end result is that you increase fuel flow during the mid-range to richen the mixture. Normally people do this to correct a lean condition caused by a exhaust swap.
Some older carbs actually have a clip on the needle and grooved slots to make them adjustable without the need for washers. Unfortunatly, modern day environmental regulations has killed off the slotted needles in most newer bikes.

Re-jetting the carbs, involves taking the carbs apart, removing the old jets, and replacing them with jets where the hole is larger. Again this increases fuel flow, richening the mixture in the mid-range. Same thing....normally done when they swap exhausts.

Shimming is the poor man's method. Re-jetting is the proper way. You have to be really careful if you dont know what you are doing. Carbs themselves are pretty simple devices....adjusting them properly for the bike is a WHOLE other deal, and adjusting them incorrectly can have catastrophic results. So if you arent familiar with working on them, its best left to a mechanic.

It should be noted that neither of these methods alone will do much for your bike. They are normally only used to correct a mixture issue caused by changing a exhaust, or changing air filters from the OEM box, to K&N's or pod filters.

When you swap out the OEM stock exhaust for a free-flowing race exhaust. It usually results in the mixture leaning out (too much air, not enough fuel). And the bike starts running hot. So to correct this, you have to change the mixture to the proper levels of air and fuel.....and this is where the shimming/rejetting procedure comes in.
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Old 07-16-2010, 12:18 PM   #13
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Thank you I would would look for someone experienced to fix it.
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Old 07-16-2010, 12:55 PM   #14
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Hi everyone, I've changed the front sprocket to 15 and the rear one is still 35. I wanted 14 but couldn't find any on the market. Hence, the ratio is now 2.33 and the result is that I've gained acceleration and my bike is okay at cruising speed.

The problem is with the 17*35 my 4th gear was going up to 110 to 115 km/h but now is up to 100 km/h. Is there something what can be done so that the effect is not that much?

Another issue is another 125cc motorcycle whose mark is suzuki have 14*39 and the bike possesses both good acceleration and very good speed. How this can be so????

Am feeling perplex please help.

Thank you
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Old 07-16-2010, 03:41 PM   #15
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Quote:
Originally Posted by echazar View Post
The problem is with the 17*35 my 4th gear was going up to 110 to 115 km/h but now is up to 100 km/h. Is there something what can be done so that the effect is not that much?
Without more adding more horsepower....no.

Quote:
Another issue is another 125cc motorcycle whose mark is suzuki have 14*39 and the bike possesses both good acceleration and very good speed. How this can be so????
Not all engines are created equal. For example...the honda rebel has a 250cc engine in it too....but its nowhere near the power of the 250cc motor in the ninja 250R. The Honda Rebel tops out around 25HP....the Ninja 250R tops out in the 32-36HP range. The difference is in the engine construction.
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Old 07-17-2010, 03:01 AM   #16
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As I mentioned in an earlier post, I've changed my 125cc cylinder to a 150cc and my original carburetor which was a deihin one to keihin one. Re-jetting have also been done by my mechanic and he changed my main jet which was 92mm to 98mm I think. Can I changed the main jet to a bigger one and does changing the pilot jet to a bigger one would have an effect on power? Mine is 32mm. In addition my cylinder head (culasse) is still the original original one. Does changing it to a 150cc would bring change?

Furthermore, the other motorcycle has not changed its cylinder but he has modified his exhaust pipe and has done carb re-jetting. The guy told me he got about 10km/h with the modified exhaust pipe which make loud noise. Can this be true because I have two exhaust pipe one modified and one original and I can't noticed any changes between the two?

Another information is that the guy and I does not have the same mechanic. Can this be an issue?
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Old 07-23-2010, 11:55 PM   #17
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WOW,...as mentioned earlier, not all motors are created equal. The Suzuki is probably capable of higher RPM's and this is why he still has adequate cruising ability. And did you say one exhaust on your bike is original and the other after market/ If so this will really cause the bike to run iradically.

Martin
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Old 07-24-2010, 09:27 AM   #18
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Hey Martin, what I think he said was that he owns both the std and modified pipes and when he try's either on the bike, there is no difference in performance other than the extra noise the modified pipe produces...
But then again I could be understanding him wrong as well... LOL...
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Old 07-24-2010, 03:31 PM   #19
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Quote:
Originally Posted by soxOZ View Post
Hey Martin, what I think he said was that he owns both the std and modified pipes and when he try's either on the bike, there is no difference in performance other than the extra noise the modified pipe produces...
But then again I could be understanding him wrong as well... LOL...
Re-read the post and you are probably right, but the broken english makes it hard to tell. LOL

Martin
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Old 07-25-2010, 04:45 AM   #20
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[QUOTE=soxOZ;724963]Hey Martin, what I think he said was that he owns both the std and modified pipes and when he try's either on the bike, there is no difference in performance other than the extra noise the modified pipe produces...

Yeah that's what I means. I own two pipes, one modified and one std and when I tried either one on the bike there's no difference at all.
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Old 08-12-2010, 01:38 PM   #21
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hey there, echazar

i purchased the same bike too and am from Mauritius too, mine is still under running-in period though and still 1 month old, but just mentioning that if you are comparing the haojue 125 to the other brands like the 'equivalent' suzuki en125-2A or yamaha ybr 125 then its true what the others say, the engine construction itself is different and the suzuki is rated with more HP (11HP vs 9-10HP) than the others. I believe the suz will still be faster even with your 150cc engine. A guy i know tuned his suz and he makes 140km with it ... but i also heard that the suz engine does fit the haojue too, since it is the same factory that makes both of the models.
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Old 06-16-2011, 01:59 PM   #22
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Hi everyone
How can we boost haojue 125 performance.............
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Old 06-16-2011, 02:33 PM   #23
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Quote:
Originally Posted by echazar View Post
The problem is that my bike is very slow at start. That is it has a very poor acceleration. Another problem is when I goes uphill I have to changed gear. Moreover, when it is in slope I have much speed but the problem is that I ride almost everytime on the 4th gear.

Can anyone help me so that I can get a good acceleration and a good speed too. If there are other modifications that I can do too...

Please note that the original sprocket is 15*39 sprocket.

Thank you
I have a 200cc chinese bike, the actual bike should not matter for the purposes of this discussion since there are some basics to how they work which apply no matter who makes it. I have been through this with mine as well and will cover what I did that helped

When you changing the gearing you alter where the power is (more or less). You may have gotten top end speed but at the cost of low end performance.

There are some jets that you can replace in the carb, these are usually simple to replace requiring only basic tools and basic knowledge. Tweaking a carb for the exact settings is specific to that bike, that carb, and the air intake, engine and exhaust that you have specifically. You may have to try a couple different jets to get it right. This can be time intensive because you have to change 1 thing then test, then change something else and test again.

For 0-1/4 throttle you generally adjust the pilot screw.
For 1/4-3/4 throttle you generally adjust the needle
for 1/2-full throttle you generally adjust the main jet

In addition you may find that a freer flowing exhaust and possibly a freer air intake could help as well. The air intake is questionable on many bikes now because they are often tuned to lower noise and in many instances, because they are resonant with the engine you will not see big performance gains however you did a big bore kit which alters that dynamic and it could be harming performance. You may have to replace the air box or drill some holes in the air box to allow for more air and air to pass more freely into the engine.

Some countries have bans on replacing the exhaust with anything louder than what came with the bike from the factory. I have heard even here in California in a couple years they are going to ban that (the law has allegedly passed and we are in the grace period now). You may want to check local laws before changing the exhaust to a higher flow system as those are usually louder as a by product of making the exhaust flow with less restriction.

The cheapest option is to rejet the carb. Main jets often are $2 here, pilot jets are often $5 and needles can sometimes be adjusted to a suitable performance level by moving the C clip to a different position which will raise the needle inside the carb. Your prices may vary given tariffs, shipping fees, etc.

There are some forums that discuss chinese bikes specifically. I do not know the rules on posting those here but I will take a gamble. Maybe someone there has worked on your bike already and can give you a starting point for jets so you do not have to buy a lot of them to test out (you will still have to test some to get optimal performance since its the totality of the system and no two bikes are 100% identical and altitude and fuel quality can also alter performance).

mychinamoto.com
chinariders.net

and I bet there are others.
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Old 06-16-2011, 02:43 PM   #24
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Quote:
Originally Posted by soxOZ View Post
The reason you have poor acceleration is the you changed your gearing from 2.6:1 down to 2.0:1...
Sometimes you want both higher speed and more acceleration. I have a 200cc bike, I went from a 15/48 to a 16/44 (and will be looking at a 42 or 40 rear today). To compensate for acceleration loss I then removed my air box and went with a K&N intake system, replaced the stock exhaust with a freer flowing one (and went from 80 dB to 84 dB which makes it annoyingly loud for me but that alone was 5% performance) and tweaked the carb (which I am still not done).

The bike now pops wheelies if I slip in any degree with my attention while pulling out from a stop, it has a lot more acceleration than stock because of the compensation work I did on the carb while maintaining a much higher top speed.

With a 125 cc big bored to 150cc I can understand the desire to regear as its cheap top speed which can help prevent being run over by other vehicles.


I forgot to mention in my previous post that a more expensive option which may or may not be available for the specific engine in question is a new camshaft. In some situations there are camshafts available that can be replaced and give you a bit more performance. My bike uses a suzuki engine made by the same factory that makes suzuki engines so I can use the suzuki after market ones, many others are Honda based and there are more after market mods for the chinese honda clones.
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Old 06-16-2011, 02:51 PM   #25
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Quote:
Originally Posted by fl-Ash View Post
the engine construction itself is different and the suzuki is rated with more HP (11HP vs 9-10HP) than the others. I believe the suz will still be faster even with your 150cc engine.
Sometimes its not the engine specifically. The cam can affect performance so can the carb. My bike uses a suzuki engine but the comparable suzuki has more HP. In part this is because both use Mikuni carbs but I have a BS28 and the Suzuki has a BS31 (its slightly bigger). This gives it a little more power even though the engine is the same.

Sometimes with a little work you can replace minor components like the cam, jet the carb, etc and achieve similar performance. Compression ratios and some other things can be altered, again by replacing parts. Depending on the total cost of everything it may be cheaper to change these components rather than the entire engine. It is also a lot of paperwork with the government to change the engine - even if it is from the dealership doing the repairs - so that is something to be considered.
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