Dong Fang DF 250 RTB Bobber Information

**Roadkill** · 07-13-2014, 07:37 PM

Originally Posted by DanDaMan

man u seriously spamming bars thread , because I can . or claim, to be able to go 13-15 mph faster than u ?

as for power to money , best buy would be a turbo , to add nuther 2-4hp , as decking/compression ect prob add 1 or 2 for a lot more time and $$ , and those numbers might all be "to hopeful"

and the motor is nearly "square" allowing a lot more power thru out the powerband , which allows a bit more pull at lower rpms , so stretching gears made sence to me

I for sure am not a mech, but I've always believed that there is a pretty much standard powerband for all 4 stroke OHV engines that can be played with by cam grinds and carb tweaks. I thought it was somewhere in the 4.8 to 5.5K range. I just got around to installing a tach on my bike and now have numbers that go with my rider feel. She seems to have plenty of torque from roll on (idle is 1800) to about 5K. Anything much above that is more noise than anything else. I'm not a speed at any cost person so I've always ridden where she feels right. On my ride, regardless of gear, that seems to be in the 5 to 5.5K range. It would be good to hear from other riders with tachs to see what their "butt dyno" tells them about the powerband.

It is my understanding that gearing is only to keep the motor in it's powerband so, you can gear for work as in a tractor, or speed as in a car. My father drove 18 wheelers and I remember that it required up to 18 gears so stay in the narrow powerband of the early diesel motors. I'm thinking that torque gets you there, but horsepower keeps you there? Anyway, has anyone seen actual dyno runs on this motor to verify powerband?

**barnone** · 07-13-2014, 09:24 PM

Roadkill,
I have a tach on my DF and I am seeing about the same power band as you. I did hit 70 MPH indicated today on a long steep downhill run at 6700 plus RPM but that doesn't count. My normal top speed is about 60 MPH indicated. No GPS to check speedometer.
She does seem to run out of juice at 5500 or so RPM.

axa,
Also saw 425 F on my cylinder head temperature gauge on a long steep up hill climb wide open throttle in 4th gear.
I eased off on the throttle and the CHT went down nicely.

Anyway, I had a nice ride on the Dragon today. She is running just fine.

**Roadkill** · 07-13-2014, 10:23 PM

Originally Posted by barnone

Roadkill,
I have a tach on my DF and I am seeing about the same power band as you. I did hit 70 MPH indicated today on a long steep downhill run at 6700 plus RPM but that doesn't count. My normal top speed is about 60 MPH indicated. No GPS to check speedometer.
She does seem to run out of juice at 5500 or so RPM.

axa,
Also saw 425 F on my cylinder head temperature gauge on a long steep up hill climb wide open throttle in 4th gear.
I eased off on the throttle and the CHT went down nicely.

Anyway, I had a nice ride on the Dragon today. She is running just fine.

I've been looking for gps speedometers for a while now but can't justify cost on a $2,000 bike. If I could find a nice 2 1/2 inch unit with turn signal and neutral indicators, I would pull the stock speedo. I had a Trail Tech computer with the magnet pickup on another ride, but just didn't like it

**barnone** · 07-13-2014, 10:45 PM

I just need to buy or borrow a GPS to see what % error I have on my DF's speedometer and I will be happy.

**axa** · 07-14-2014, 03:37 AM

Originally Posted by barnone

I just need to buy or borrow a GPS to see what % error I have on my DF's speedometer and I will be happy.

I measured the DF stock speedometer to be almost exactly 10% over.
I cant say for sure if it is linear, but the mechanics of it lead me to believe so.
That has proved accurate enough for me... an easy calculation to do in your head and get to keep your stock spedo.

**Roadkill** · 07-14-2014, 11:55 AM

Originally Posted by axa

I measured the DF stock speedometer to be almost exactly 10% over.
I cant say for sure if it is linear, but the mechanics of it lead me to believe so.
That has proved accurate enough for me... an easy calculation to do in your head and get to keep your stock spedo.

It's one of those cosmetic things, actually. 10% at 60 mph isn't that important to my daily riding style. The stock one isn't ugly but if can get a different look plus accuracy for not to much cash I'll do it. I only gave $17.00 for the tach new and mounted it on the choke side of the bars. I 'm looing for the speedo or an anolog oil pressure or temp guage to mount on the other side.

**axa** · 07-14-2014, 12:44 PM

Originally Posted by Roadkill

It's one of those cosmetic things, actually. 10% at 60 mph isn't that important to my daily riding style. The stock one isn't ugly but if can get a different look plus accuracy for not to much cash I'll do it. I only gave $17.00 for the tach new and mounted it on the choke side of the bars. I 'm looing for the speedo or an anolog oil pressure or temp guage to mount on the other side.

how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

**Roadkill** · 07-14-2014, 01:01 PM

Originally Posted by axa

how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

That.s what I'm thinking also about the oil, but I keep looking for something that might work with a mod. For temp, I'm thinking a digital unit with the display mounted in a speedo type case might be nice. I just don't like the space ship look of most of the factory units. I had the Trail Tech computor that had lots of good info, but it was always in the wrong screen for what I wanted and it was also ugly! I've used several of the digital ones from China for less than 10 bucks in my work. Many of the big rigs have a pyrometer mounted on the stack also.

**Woody87** · 07-15-2014, 02:08 AM

Just a quick heads-up to you DF owners,

I posted some time ago on changing out the stock coil for one of the orange "performance" coils from Amazon. As it turns out, the coil was the cause of my speedometer not working with the engine running unless I unplugged/reconnected it. It leads me to believe that either my coil was not grounding properly, or that the style of coil itself is not sufficient for use on our bikes. It took me taking a good month's break of messing with the bike and focus on my 280Z, only to come back and resolve the issue in about 15 minutes. Just want to save you guys some headache should you consider the coil swap, or have already swapped and have the same issue.

**barnone** · 07-16-2014, 02:19 AM

t

Originally Posted by axa

how could one install an oil pressure gauge on an 167fmm without machine work?
i dont reckon you could, else barnone would have it already, wouldn't you barnone....
though that oil temp thingy he has is pretty cool, id like it in analog...

The oil temp thingy that I have is not an oil temp thingy but a cylinder head temperature thingy. Never felt the need for an oil pressure gauge.

I just ordered this http://www.aliexpress.com/item/CG125...974573329.html but in a black radiator. Perhaps an oil temp and/or pressure could be incorporated with it?