Dong Fang DF 250 RTB Bobber Information

[branden84]

im tryimg to decide on a sprocket size to go with. im thinking 37 might be the one. im about 190lbs and would like to be able to get up any hills i may come across at 50-55mph. my usual trip to work is mostly 30-40 thru town but there is a strip of 2 miles thats 55 with 2 long hills. most people drive 60-65 thru there and i would like to keep up the pace. what sizes have others went with and how do they work for you?

[GUN ROD]

im tryimg to decide on a sprocket size to go with. im thinking 37 might be the one. im about 190lbs and would like to be able to get up any hills i may come across at 50-55mph. my usual trip to work is mostly 30-40 thru town but there is a strip of 2 miles thats 55 with 2 long hills. most people drive 60-65 thru there and i would like to keep up the pace. what sizes have others went with and how do they work for you?

Due to Illinois flat roads, I went with a 35. Sorry that I did, when I do run into hills, no guts. Fast on the flat & nice rumble in town.

[rollenrock]

I went with a 37. I have 8% grades that I have to go up on every ride. They are long, winding hills, and with my 37 I can hoover around 70 mph.

[ghost1133]

I went with the 38 tooth sprocket, from instinct I guess. Worked out great. I did this with going from a 45 tooth sprocket, (stock). I could go smaller or larger. $29.00 a shot. But the 38 did the trick for me. I weigh about 190. From the take off, I would be hesitant to go smaller. But then the sprocket is so easy to change out, I might try a smaller one. Just for fun. That is when I get the leaking gas tank thing corrected.
So now I am going to light up a fire.
I have been on two wheels for 30 years plus. This is a good bike. But really, does anyone on here think that speeds exceeding 60 mph. is a good idea with only a 250cc.

"I don thin so Lusy" Don't get me wrong. I love this bike.

But with speed you need power. This bike does not have enough torque to get you out of trouble over 60 mph. If that.
What do I mean by that?
That's why they come with a 45 tooth sprocket. Once you exceed the torque your bike is capable of, well put it this way. It would be like free wheeling a mountain bike down pike's peak. No matter what speed you are going, if you cannot kick it in the butt. You are going down. That said.
I might try the 35 tooth.

[rollenrock]

I agree with you, Ghost. I don't like full throttle just to keep up with traffic. I like having a safety net and being able to get out of the way. The road I travel is fortunately two lane each direction, and the hills slow down all traffic. I won't take mine on the freeway, and I don't like to push it all the time. I'm about 140, so I have a little less to carry around. I might try a new jet to see how much it'll improve things, but if I had to travel 65+ consistently for a great distance, I'd get a bigger bike. I heard that 400 cc engines might be coming out. Of course I won't hold my breath, but I would probably snag one up if it was offered.

[DanDaMan]

im happy to run on freeways in it , but in the slow lane generally , while watching rear views (dern texans think its a race to get everywhere and think its a game to speed as much as possible below ticket levels -ie- 9 over the limit here u cant be ticketed even on an 80 or 85 mph roadway

that said I have hit 80 (indicated) on mine on level ground , with what seems to be a bit more motor left in it (worn tire shake slowed me to more reasonable speeds) , but do lose speed slowly on hills but never fall below 65 even in top gear , and man it sounds great at 65 (indicated)

36 tooth rear sprocket but front fits a 17 tooth , thanks to using a 428 DID chain instead of the 520 chain the bobber comes with (effectivly running a 33 tooth rear sprocket) but I only weigh 165

although still a bit lean on the freeway because of the air ram

joining the "darkside" tomorrow , although may need to remove and or modify fendor/mounting of fendor to accomidate the car tire , and DynaBeading it http://dynabeads.net/ to permanantly internally balance it

I am perfectly happy with its limitations and nursing what I can from her , if I want more I'll find an old 2000-12 CBR250R motor and bolt it in , that 6 speed and claimed 30ish hp (about 3 times the HP of our bikes) in a single cylinder thatll fit the frame looks interesting

[branden84]

it would be nice to know what engines use the same bolt pattern for mounting. to know what options there are for swapping. dirt bikes all use single cylinder engines. i think ill go with the aluminum 38 tooth. anyway to save weight transfers to a better power/weight ratio. i might replace the rims with aluminum as well, after hearing how quick they rust. i was quoted 104$ for the first year of insurance (on a permit). i will be signing up for the msf class soon. next available in my area is scheduled for the end of july. i am planning on ordering the bike a week before the class ends. to try and time everything right i will have the bike, lower insurance rate, and license all at the same time. the hardest part is waiting!!

that u-turn intake sounds like a great idea. what size tubing did you use? and do you think there is a less restrictive alternate filter to use?

i'm also thinking that removing the muffler and welding a slightly smaller diameter straight pipe slightly longer would change the power band a little. the diameter and length would create the backpressure needed for low rpm torgue and the straight thru design would let it breathe for high rpm hp? any one else agree/ disagree?? my logic may be wrong but i wont be expiramenting until next year or so. (unless theres some nice days in winter)
im not sure thats the route i want to take yet. i know its going to be louder. maybe just swap the muffler for a thrush glass-pack.

*ny state does not require emissions test for inspection.

[DanDaMan]

I believe the motor is a small honda bolt pattern , dont recall size of hose on u bend into airstream (carry u filter into store for sizing) , and the motor is a pushrod motor no matter what u do the "powerband" will be right near 1/2 to 3/4 throttle past that your "screaming the motor" for little to no benifit (probably actually producing less HP near max RPM's than at 3/4 throttle) , thats why I geared mine so @ 62 thru 72 or so Im in the powerband instead of 55-65 being my entier powerband

manual states max HP (12) is produced at 6500 , pointless running the bike over that , ever :p

[branden84]

good to know. thanks Dan

[ghost1133]

I heard that 400 cc engines might be coming out. Of course I won't hold my breath, but I would probably snag one up if it was offered.

Hey.
Rollenrock, as soon as you hear about this 400 cc engine. Shoot me a line.

P.S. I'm holding my breath "gasp"
Don't get me wrong, I like this bike. But willing to explore new possibilities.