Dong Fang DF 250 RTB Bobber Information

[axa]

Thanks Axa,
Yup, I had scoop facing the wind direction.
Will experiment the stock filter and the scoop again in the future

So, it's normal for the sputtering at top speed. That sucks.... So I guess my top speed is 55mph, sucks even more

Yes, though I said sputter is common not normal, by no means should you accept it. It can be eliminated tuning your airflow, I know that for a fact.
For me it meant top rpm from 6.5k to 7, with allowed a few mph increase on top end in the most optimal conditions. For me that is a very worthy modification.
I haven't even touched my jets or needle yet.
I will when i find a proper air scoop Ill try bumping the main jet way up, but I'm not expecting much if any improvement on the top end from it.

I saw that scoop you bought off ebay sometime ago, but speculated it was too aggressive as it has a very concaved intake. You seem to have confirmed that.
I am looking for one with a wider area but no concavity, or even some convexity.
I may need to fabricate something when time allows, cuz i am not finding what i want.

So that's why i feel the most important mods you can make to improve the top end is lowering your sprocket ratio, and eliminating any sputter.
Ultimately, this bike's top speed will largely depend on its lack of power because of drag.
And at highway speed the resistance apparently increases by an exponent. Here is an interesting read about it click to see the full article:
At low to moderate speeds, during stop and go driving for instance or while you're motoring around town the affect of drag is negligible, don't confuse this to mean non-existent, any serious bicycle racer can tell you it isn't, but as far as motor vehicles go, as long as we stay under about 50 mph it accounts for only about 5% of a vehicles total resistance to movement. Unfortunately once we reach highway speeds, roughly 60% percent of a vehicle's energy is required just to defeat air resistance, and that grows exponentially as speed, and with it air velocity, increases. If you've ever fought a stiff headwind you know exactly what I'm talking about. Riding into the wind you have to twist the throttle up like an alarm clock spring just to maintain headway. With the wind at your back, you can reach the same speed on half the throttle. Think of drag as a never ending headwind, and you won't be far off the mark.

[Chi town]

Thanks Axa

[barnone]

Sorry Barone, I read the first 250 pages of this thread and from the time you came back on this thread. It seem the sputtering at top speed wasn't mention much till a few pages back till you said something.
Question Barone, as I am not so well knowledge about motorcycle mechanic. When you took off the air cleaner, did you had to adjust the air/fuel mixture as well?

Chi town,
I just removed the air cleaner and did not change anything and she ran up to max rpm without sputtering. I put the air cleaner back on and and she sputtered so I assumed that the stock air cleaner is too restrictive for my DF with 108 main, 42 slow, and the catalytic converter removed. I could be wrong.

She pulls real good up to about 5500 RPM when the cutting out occurs with the stock air cleaner installed. I ordered some other air cleaners off Ebay to try. Might go back to a 105 main to see if the sputtering stops but will wait for the new air cleaners.

I had a 2010 DF and don't remember having this cutting out problem.

[Chi town]

Thanks Barone

[axa]

Axa,
You mention that the air scoop filter I have brings much more air in. If I decide to use that air scoop in the future, will that mean I need a bigger main jet and maybe raise the jet needle some more?

I don't honestly know if you will ever be able to balance that scoop, but my speculation is the convexivity is just too much, thus catching too much air at speed.
if it was dying at a particular throttle % you could try particular carb adjustments.
but I don't know what the cure would be for too much air at higher speeds without effecting performance at lower speeds.
try running with some choke applied, but as you bumped your needle and perhaps ur mechanic increased the throttle on your piolt jet with the air/fuel mix screw, less air is not likely what is needed at these points.
you could manually apply the choke at speed but that would get annoying.

anyway I would recommend making as few adjustments at a time, learning from them as you go

[Bobthebobber]

Sorry, I will have pictures of my DF later.

I forgot to mention that the stock headlight was dimming as I revs the engine and that the headlight gets brighter as I applied the brakes. I have not ridden the bike at night since changing the new led halo headlight, but I seem to be ok now.

Yea thats a weird thing I keep meaning to post. My headlight dims as the bike revs and it gets brighter when I hit the brakes. The 2012's seems to be coming rich from the factory so i would change back to the 105 main and remove those needle shims. I was having cut outs also.. I took my entire carb apart... and re-adjusted the air fuel fix.. put the stock jets back in... I also changed to a closed ended air filter with better filtration. I am able to creep over 60 mph on flat ground now. First and second gear are almost useless even with a 35 tooth. First gear should have the most torque but it feels crap.. second is about the same.. but once into 3rd it feels like a different machine. Much more power 3-4-5 than 1 and 2. Sometimes it's embarrassing to have to full throttle the first 3 gears just to keep up with the acceleration of traffic...and everyone looks at you because the bike sounds like your going 100 when you are just struggling to get to 25mph. Idk.. each bike is a little different even though they are all made the same way... because these are cheaply made Chinese bikes. with poor quality control at the factory... the specs may not all be exactly the same.. and im almost 100% sure things do not get adjusted to spec (valves, carb, chain) so you just need to keep fiddling with it.. You'll get it there eventually.. I have my carb with stock jets.. with the mixture set just about 2.5 turns out maybe a hair less. I have yet to check my new plug... but regardless if it is running rich or lean with my current setup... it drives perfect with no cut outs.. so Im not going to touch it.. although i may try the ram air just because it looks cool visually. Good luck with the bike!



Can you link us where you got the headlight and the turn signals?

[Bobthebobber]

okay i just bought a set of these http://cgi.ebay.com/ws/eBayISAPI.dll...tchlink:top:en

I think this should drop the bars about 2 inches from where they are now. I want them down low.. not quite cafe racer low.. but I think they look a little off with the stock setup

[axa]

Yea thats a weird thing I keep meaning to post. My headlight dims as the bike revs and it gets brighter when I hit the brakes. The 2012's seems to be coming rich from the factory so i would change back to the 105 main and remove those needle shims. I was having cut outs also.. I took my entire carb apart... and re-adjusted the air fuel fix.. put the stock jets back in... I also changed to a closed ended air filter with better filtration. I am able to creep over 60 mph on flat ground now. First and second gear are almost useless even with a 35 tooth. First gear should have the most torque but it feels crap.. second is about the same.. but once into 3rd it feels like a different machine. Much more power 3-4-5 than 1 and 2. Sometimes it's embarrassing to have to full throttle the first 3 gears just to keep up with the acceleration of traffic...and everyone looks at you because the bike sounds like your going 100 when you are just struggling to get to 25mph. Idk.. each bike is a little different even though they are all made the same way... because these are cheaply made Chinese bikes. with poor quality control at the factory... the specs may not all be exactly the same.. and im almost 100% sure things do not get adjusted to spec (valves, carb, chain) so you just need to keep fiddling with it.. You'll get it there eventually.. I have my carb with stock jets.. with the mixture set just about 2.5 turns out maybe a hair less. I have yet to check my new plug... but regardless if it is running rich or lean with my current setup... it drives perfect with no cut outs.. so Im not going to touch it.. although i may try the ram air just because it looks cool visually. Good luck with the bike!



Can you link us where you got the headlight and the turn signals?

I don't personally believe it's a much a problem with quality control out of china.
Surely they are not adequately installing valves, i cant argue with that at all.
But my carb was marked and adjusted, likely to their factory settings when they ran and tested the engine. I would argue they must adjust all to settings that would run at their factory.
And we can debate if a snug chain is improper on a bike with no suspension...
I would argue its adequate if not superior to one that is loose.

But rather the variances are in each of our individual conditions and perceptions.
For instance, many of us have the cut out problem, which by all accounts is a starvation for air @ WOT top rpm and the engine riches out. But the first thing so many of us are doing is upping jets and shimming needles to make an an even richer mix...

Which leads me to ask about this filter you had added which apparently solves this max rpm sputter. If it is not reversed or otherwise catching air, I question what would lead you to believe it had "better filtration"?
For a better filtration by definition will add to the impedance of air flow, so this is not making sense to me.
Not trying to be a douche, just curious to learn if there are indeed factual differences in airflow for different filter designs. The stock mushroom type vs the closed end type you purchased.
If there is a filter design that in fact catches smaller particles and provides better airflow, without having an enlarged filtration area, id like to use it instead of being on the hunt for an adequate scoop that seeming doesn't exist.

its a 0 sum game, im either pointing a more restrictive, better filtering device into the wind, or your using a less restrictive poorer filtering device in stock configuration, or perhaps it has an enlarged area compared to stock.

Would you post the measurements of size of your filter's element area? and/or a link to it?

[Chi town]

BobtheBobber,
I got the headlights from eBay. The seller is called chevyracer57. The item description is 5-3/4 white halo halogen h4 bulb headlight angel eye led.
image.jpg
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The turn signals I bought from amazon.
Sorry I can't get a copy of the Internet address, but you should be able to find those in amazon by punching led turn signals.
I kinda regret that I bought the chrome. As with the chrome on our DF, these chrome led turn signal are cheap. The rear led turn signal wires were short, so if you decide to buy, expect to have wires in hand for extension

[Chi town]

Anyone think I should buy a tachometer? Will a tachometer make tuning easier for me and more precise?
I haven't had any success in tuning the carburetor. It seems I can never get it right.