Dong Fang DF 250 RTB Bobber Information

[4950cycle]

Is that you Prodigit from the scooter forum ? Anyway, These OHV only have so much HP. If you gear them to tall they won't pull the gearing unless your 5'5 and 105 lbs.. I'm 6'3 and 255 lbs. I changed my factory gearing to 16/38 . It was just a little to tall. Just wouldn't pull it worth a darn with my big wind catching ass on it. I had to drop one tooth on the front (worth 3-4 teeth on the rear) At 62 indicated (actually 57 or 58) and got 80 MPG . That's about the best I can do with it. Hell, my Ninja 250 can get 70 or better at that moderate speed.

[GonzoX]

Is it just me or can everyone else make heads or tails of this?

maybe you should start that RTC thread...

Its all rocket science and greek to me LOL. Not that advanced. All I want is a reliable bike mainly. Will work up from there. So far she has not let me down but there are a few issues that I still have to address. Tank leak is #1 issue but its a slow leak. Other than that she runs and she gets me accross town. Happy about that. My main issue is the poor mettalurgy and rust right now.

Love the info and will record it and save it for the future for sure. It will come in handy later Im sure. But Im still a noob so Im just recording it and saving it right now LOL.

I do agree about the stock gearing though. Good God I have to change gears three times just to get out of cars ways after a red light. But I expect that from a sub 250cc engine. That's why Im going to ask axa for a loan to buy something with 500cc or bigger.

In all honesty I was going to buy two sub 50cc scooters for the same amount hoping that my new wife would warm up to hers. I am SOOOOOO glad I got this instead. Sometimes ya just gotta splurge on yourself because nobody else will. That's for damn sure. No regrets!

Now where did I put my rum?

[ProDigit]

Is that you Prodigit from the scooter forum ? Anyway, These OHV only have so much HP. If you gear them to tall they won't pull the gearing unless your 5'5 and 105 lbs.. I'm 6'3 and 255 lbs. I changed my factory gearing to 16/38 . It was just a little to tall. Just wouldn't pull it worth a darn with my big wind catching ass on it. I had to drop one tooth on the front (worth 3-4 teeth on the rear) At 62 indicated (actually 57 or 58) and got 80 MPG . That's about the best I can do with it. Hell, my Ninja 250 can get 70 or better at that moderate speed.

Yup, is me.
On the BMS TBX260 I have a 100:1 ratio RPM over MPH, and the bike goes 82MPH. It's 256cc fuel injected though...
I use this RPM over MPH ratio, because it's indiscriminate against CVT or manual geared bike.

On the 150cc TaoTao I have a 116:1 gear ratio (or 7k RPM @ 60MPH); and it tops out at 63MPH GPS verified.

Those bikes accelerate just fine, save for near the end of the variator, where speed creeps those last 10-15MPH to top speed. You know that on those scooters they have maxed out their gearing on those engines.

I know they are different engine types, but even with different engine types, you should get a certain amount of speed for a certain amount of CC's.
The Bobber is probably the least aerodynamic bike of them all (RTA, RTC, RTC-B, RTD); so wind drag may eat a couple of mph from the top speed.

If the gearing is too heavy, you could always upshift one gear, for better acceleration.
I guess I'm lucky at 100LBS lighter.

BTW, I finished reading the first 114 pages of this thread.
Seems like some people get the RTB-A (which is with black hardware) and some get the regular RTB (with chrome hardware).
Get the RTB-A if you can. Black means less rust!

[axa]

That's why Im going to ask axa for a loan to buy something with 500cc or bigger.

your loan has been approved!

but what in tarnation makes you you believe that i have any money

i really want more engine. ive been scouring craigslist

[SR.MAILMAN]

i really want more engine. ive been scouring craigslist

Consider a USED(low price) Honda Rebel 250/234cc or a Yamaha XV250/249cc motorcycle. Both have been around for over 20 years and can be "modded" into bobbers. They are solid enough so that age really does not matter(parts have remained available and unchanged over the last 10 years).

C.A.R.B. compliant too!

[barnone]

i really want more engine. ive been scouring craigslist

axa,
I ordered the engine you PMed me about but it turns out to be an ATV engine and the price was wrong. So the guy is refunding my money.

His email. Honest mistake. We knew it was too good to be true.

"Hi Vincent, turns out I made a mistake, actually 2.
First it’s the wrong engine, you need 65534 (I have modified the description)
I also messed up on the price, I had most of them ok but the 65532 was wrong at $494.93 it’s actually under my cost plus I need to cover for shipping.

So here are the options, I can refund you for the order or you can pay an extra $230 for the 65534 engine?

Let me know what you want to do, I’m very sorry about this."

Now corrected listing at
http://www.mbe-motorsports.com/catal...roducts_id=388

Correct engine for our DFs at
http://www.mbe-motorsports.com/catal...roducts_id/389

Still tempting but the search continues. Maybe a "big bore kit" is the way to go.
Now that I have the cutting out problem solved with my new foam air filter I'm good for a while.

[axa]

Consider a USED(low price) Honda Rebel 250/234cc or a Yamaha XV250/249cc motorcycle. Both have been around for over 20 years and can be "modded" into bobbers. They are solid enough so that age really does not matter(parts have remained available and unchanged over the last 10 years).

C.A.R.B. compliant too!

i would hesitant and not too unsure to say that neither of these motors will fit.
The dual exhaust on the rebel will not fit nicely with the double cradle.. i dont know what the frame is called but to split cradling tubes on our bike will get in the way of the dual exaust.
I would also be hesitant and say the V cylinders on the Yamaha would be a tight if not impossible fit. Our carbs with filters hardly do.

Else i would have this already!!! yup thats right Honda Rebel with 950 miles 500$ screw the title work.

[axa]

axa,
I ordered the engine you PMed me about but it turns out to be an ATV engine and the price was wrong. So the guy is refunding my money.

His email. Honest mistake. We knew it was too good to be true.

"Hi Vincent, turns out I made a mistake, actually 2.
First it’s the wrong engine, you need 65534 (I have modified the description)
I also messed up on the price, I had most of them ok but the 65532 was wrong at $494.93 it’s actually under my cost plus I need to cover for shipping.

So here are the options, I can refund you for the order or you can pay an extra $230 for the 65534 engine?

Let me know what you want to do, I’m very sorry about this."

Now corrected listing at
http://www.mbe-motorsports.com/catal...roducts_id=388

Correct engine for our DFs at
http://www.mbe-motorsports.com/catal...roducts_id/389

Still tempting but the search continues. Maybe a "big bore kit" is the way to go.
Now that I have the cutting out problem solved with my new foam air filter I'm good for a while.

the while you will be 'good' for, is about a week....

whats the difference in the links? they still look the same except for the part number.

Should have figured though, from his initial answers it sounds like he hasn't ever even sold one of these...


id be all over a bigger bore. It would likely be the least costly, and provide me a practice cylinder to learn to bore on my own.

[GonzoX]

your loan has been approved!

but what in tarnation makes you you believe that i have any money

i really want more engine. ive been scouring craigslist

I know bro, Im just kidding.

I know what I want but its $7k. A Royal Enfield. Only other issue is Im a short fat old guy and Ill have only one foot on the ground on one of these since the bullet is something like 6inches higher than my DF. Been told that this should not be an issue since many riders have bikes and use only one foot at park or take off. I hope they are right but Im a noob and this seems a bit uncomfortable to me. Ill trust the judgment of veteran riders though.

I do have my eye on a Honda 750 and it feels good. Both feet flat on the ground and it has more power. Its used and costs about the same as a new RE. Thing is, I have this longing for a retro bike and both the DF and the RE fit that niche. The older bikes just look right to me for some reason.

And for the record I will be watching any engine swap outs here with a microscope. AFAIK this has not yet been done on the DF. Should be an interesting if not entertaining thing to read about. Just dont see a whole lot of room on the frame for anything bigger unless it has a bmw style engine with the heads and cylinders on the sides. And IMHO that would look all kinds wrong on the DF. Not to mention that I think BMW has a trade mark on this like Harley did on the V way back when (Ural doesnt count) LOL.

[SR.MAILMAN]

Stay with the used Honda shadow 500cc or bigger,if the budget allows.

I researched a new Royal Enfield and what I discovered is that they upgraded the fueling to EFI and ignition to solid state.
The improvement did little for gas mileage and you still have the OLD base engine(push rod).

My Yamaha will keep up with one,due to horsepower to weight difference.

As you can see from My signature, I ended up with a Triumph T100 (looks like a 1960's model) has state of the art hidden components.
I was able to gain 12 rear wheel horsepower, just by "adjusting" the engine management in the ECU.
I do not want to go fast, but I do want what the engine puts out... before the EPA got to it.
53mpg is MORE than a 47mpg stock engine put out. This is My long haul/highway machine(when I need to go faster than 50mph).