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Post by Alleyoop on Mar 2, 2014 16:56:13 GMT -6
Haven't read the whole deal, but I have a Dong Fang 250 rtb-B and it came with a 45T rear sprocket. I changed it to a 38T and it performs much better. Several of the Dong Fang models seem to be shipping with the 45T sprocket. OK for a dirt bike maybe? Great another one with a Dong Fang, so with the 45T rear sprocket what was it running at and at what rpms? Of course going down on the rear sprocket to lesser teeth and or the front sprocket to more teeth is going to give you higher top end. But if your motor does not have the power changing to taller gearing will make it sluggish starting off and getting up to speed. Alleyoop |
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Post by kz1000st on Mar 2, 2014 17:40:48 GMT -6
If you notice there is no speedometer on the bike. I'm only guesstimating it. Yes, it's my bike. Would you like me to print the other picture I have of it and the result sheet from 1971 with my name and Jimmy Adamo's name on it? I don't have to fake my past. Take a picture of someone indeed!   Haven't read the whole deal, but I have a Dong Fang 250 rtb-B and it came with a 45T rear sprocket. I changed it to a 38T and it performs much better. Several of the Dong Fang models seem to be shipping with the 45T sprocket. OK for a dirt bike maybe?Exactly my point. Test for clutch slip the way I said, before you tear into it. If it came from the factory goofed up a new clutch won't help it. OEM Stock Sizes for a 2009 Honda Rebel 250 - CMX250C
For reference only. Please verify with owners manual.
Chain Type: 520 Chain Length: 108
Front Sprocket: 14T Rear Sprocket: 33T |
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Post by Alleyoop on Mar 2, 2014 18:08:12 GMT -6
You can put up all the pictures you want that show you can ride, BUT that does not mean you know what makes what tick. Take the professional drivers, Nascar, Dragstrip etc.. they know how to drive but ask them to fix something and they are lost.
It doesn't take a genius to see it's his clutch he can barely get it to 30mph then needs a heck of a lot of rpms to get to 40. Even the huge SPROCKET that is in the picture of the bike would do a hundred times better than that. If It was the sprocket being to big it would get to speed quicker than snit but not much top end. You got's to know how this stuff works otherwise you just confuse the person with the problem and he then doesn't know right from wrong.
I cringe to hear what you would say if that same thing happened to a ride with a CVT.
Alleyoop
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Post by racerx125 on Mar 2, 2014 19:14:41 GMT -6
well I did the test KZ said and when when jumping to 5th engine nearly wanted to stall even if giving full throttle and engine revs drop and started rising slowly with speed rising at same time
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Post by stevespidel on Mar 2, 2014 19:31:02 GMT -6
I changed mine shortly after purchase. At another website they are saying in the 50mph range and most owners are switching to 35 or 38T. At 45T, I was in 3rd gear at about 25-30 mph. 35T is a little tall for hill country. I didn't need to shorten the chain to get proper adjustment, but the wheel was back far enough that I was worried about fender clearance so I took out 3 1/2 links. There isn't enough room under the cover to change the countershaft sprocket without changing the 520 chain down to something smaller. I don't expect to see much over 60mph with mine, but it's not bad for city or short highway runs. For sure, not a freeway bike. My version is a hardtail springer so 60 is fast enough for my old bootie. Listed as 250cc but it's really 229cc.
With all that said, she seems to be well built and after the rather easy setup she started right up and runs well. I have had to adjust the clutch cable several times to allow for stretch. His should be past that new bike stretch. She is pretty much in the same class as a scooter more than a practical highway cruiser. My YY250t and my 150cc Ice Bear Viking are both faster.
If it's allowed, I can post the name of another website that has an extremly large thread dedicated to the Dong Fang.
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Post by kz1000st on Mar 2, 2014 19:37:25 GMT -6
well I did the test KZ said and when when jumping to 5th engine nearly wanted to stall even if giving full throttle and engine revs drop and started rising slowly with speed rising at same time The clutch is fine, your gearing is wrong. Another botch job by Sunny Sports. Thank you. |
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Post by racerx125 on Mar 2, 2014 19:41:29 GMT -6
well I can only reach 5th gear as it has no 6th and by gearing you mean the gears inside the engine? if so do you know a place where I can buy the one I need?
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Post by stevespidel on Mar 2, 2014 19:54:01 GMT -6
well I can only reach 5th gear as it has no 6th and by gearing you mean the gears inside the engine? if so do you know a place where I can buy the one I need? Don't know if you're replying to me or not but gearing in my case means change either the rear sprocket or the front (countershaft) sprocket. It's not a technical job, but the rear wheel has to be removed and I needed a breaker bar to loosen the nuts holding the sprocket to the wheel. I'm sorry but I can't remember where I bought the sprocket but they had a large selection. I couldn't advise you on the correct one because mine has an 18" spoked rear wheel and I couldn't even begin to guess what might work with your version. |
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Post by racerx125 on Mar 2, 2014 21:28:21 GMT -6
well steve My rtc has a 428H chain with 100 links also luckily I removed the rear fender so fender clearance isn't much of a problem mine has 17t on front and 46t on rear if you could remember that place where you bought your sprocket I will forever be grateful because finding a 6 bolt sprocket to fit is very frustrating. It appears Google is not my friend anymore :/
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Post by Alleyoop on Mar 2, 2014 22:04:13 GMT -6
well I did the test KZ said and when when jumping to 5th engine nearly wanted to stall even if giving full throttle and engine revs drop and started rising slowly with speed rising at same time The clutch is fine, your gearing is wrong. Another botch job by Sunny Sports. Thank you. Just want to make sure this bit of information is not lost. Alleyoop |
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Post by racerx125 on Mar 2, 2014 22:46:11 GMT -6
How so alley? did one of us say something wrong?
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Post by stevespidel on Mar 2, 2014 23:01:10 GMT -6
well steve My rtc has a 428H chain with 100 links also luckily I removed the rear fender so fender clearance isn't much of a problem mine has 17t on front and 46t on rear if you could remember that place where you bought your sprocket I will forever be grateful because finding a 6 bolt sprocket to fit is very frustrating. It appears Google is not my friend anymore :/ It was Old Bike Barn. They sell quality sprockets. My 38T sprocket was about $30. My chain is 520 by 128 link roller. If yours is 17/46, your final (2.07) might be close to what that engine can handle. Alley was correct when he said that top end might improve if your engine can handle a smaller sprocket but acceleration will suffer. Always a trade off, huh? You might take a look at My China Moto for a little more info on Dong Fang. |
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Post by Alleyoop on Mar 2, 2014 23:32:14 GMT -6
No, nobody said any nasty stuff just a big disagreement is all. I can tell you this, if your motor cannot pull the current sprockets which are right on for 50+ mph and you currently can only get it to 35 at 8500 rpms something other than your sprockets are at fault is all I have to say. I mean really just think about for a minute, a 50cc or a TOMOS MOPED with what, the most 3HP pulling 15/51 gearing can keep up with your 250cc bike. I wish others with experience would chime in to help your cause. Take a video of the bike on the stand and lets see how it runs while you give it throttle and see the rear wheel spinning. Have you adjusted the carbs fuel ratio mixture? If not here is how to adjust it. Have you adjusted the valves? scooterdoc.proboards.com/thread/1499/4ts-carb-tuningGood Luck and ride safe. Alleyoop  |
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Post by racerx125 on Mar 2, 2014 23:57:58 GMT -6
So Slow acceleration means Slower take off speed and will take a while to reach max speed and faster acceleration will mean I will get less max speed but in exchange get faster take off and ability to reach top speed?
All I want is to be able to drive at 60-65 mph mainly becuse it's the primary and the only ride I have and I need to find a way to get it fixed properly because I can only drive in 35 mph streets otherwise I will run the engine at redline just to be able to drive around.
I mainly would Love to make it good enough to drive on I-10 for a few minutes, currently I have to spend lots on gas because I need to drive around the Interstate to evade those 65 mph speeds and I also need to be careful because the only way of cooling the engine is air flow mainly because this motorcycle does not have an oil cooler or any kind of cooling system
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Post by stevespidel on Mar 3, 2014 4:45:24 GMT -6
I mentioned the rear sprocket because my Dong Fang came with 13/45 sprockets and changing to 38 made a big difference. If you're at 17/46, I agree with Alley that your problem is most likely not gearing. This is such a basic question that I hesitate to ask, but does it "feel" like you're doing 35-40 at 8.5K? Is there a remote possibility that you're speedo is jacked?
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..BAD TO THE BONE..
