Dong Fang DF 250 RTB Bobber Information

[Chi town]

Hello everyone,
First of all, I like to thank everyone for all the great info. The info provided by ya has fixed some of the problems i had. Thank you guys. I bought my 2012 DF250 RTB-A from Killer Motorsports at the end of June and received the DF in the middle of July. Since then, I have not received my papers to register the DF. I regret buying from Killer Motorsport as they customer service sucks a$$.
Anyways, my problem with the DF is that I can't seem to get pass 55mp without the engine sputtering or choking, or it seem as it is cutting out.
When I first got the DF, it felt as the riding was heavy and it picked speed slow. But after reading this great forum, I adjusted the valve on the crank and the DF became better. The valves had no gap what so ever.
Here is a list of mods I have done to my DF:
- close out the secondary air system ( as it kept busting the hose)
- change the stock swear sprocket to a 35 tooth
- added a 108 main jet, and the mechanic did something to the pilot jet where it acts as a 45 pilot jet
- added 3 washers to the needle jet
- tried a reverse air ram with the new filter I bought on eBay. ( I will post that air filter pic soon) the reverse air ram didn't work as I was going 35-40 mph the engine would just die out. Put the stock filter back on and the engine did a lot of sputtering around 40 mph. So, I tried this other filter I ordered on eBay that looked similar to our stock air filter except it has a plate cover on top of the air filter. That filter resulted a smoother ride till the problem I'm having around 55 mph.
- changed all turn signals to led, along with a new led halo headlight
Is anybody having trouble at high speed (around 55 mph) were the engine starts to sputter? Also, after changing to a 35 tooth rear sprocket I expected the DF should not have a problem going above 55 mph. Is that normal???
Sorry for the long post.
image.jpg
image.jpg

[Chi town]

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.

[BobbinInTexas]

Hello everyone,
First of all, I like to thank everyone for all the great info. The info provided by ya has fixed some of the problems i had. Thank you guys. I bought my 2012 DF250 RTB-A from Killer Motorsports at the end of June and received the DF in the middle of July. Since then, I have not received my papers to register the DF. I regret buying from Killer Motorsport as they customer service sucks a$$.
Anyways, my problem with the DF is that I can't seem to get pass 55mp without the engine sputtering or choking, or it seem as it is cutting out.
When I first got the DF, it felt as the riding was heavy and it picked speed slow. But after reading this great forum, I adjusted the valve on the crank and the DF became better. The valves had no gap what so ever.
Here is a list of mods I have done to my DF:
- close out the secondary air system ( as it kept busting the hose)
- change the stock swear sprocket to a 35 tooth
- added a 108 main jet, and the mechanic did something to the pilot jet where it acts as a 45 pilot jet
- added 3 washers to the needle jet
- tried a reverse air ram with the new filter I bought on eBay. ( I will post that air filter pic soon) the reverse air ram didn't work as I was going 35-40 mph the engine would just die out. Put the stock filter back on and the engine did a lot of sputtering around 40 mph. So, I tried this other filter I ordered on eBay that looked similar to our stock air filter except it has a plate cover on top of the air filter. That filter resulted a smoother ride till the problem I'm having around 55 mph.
- changed all turn signals to led, along with a new led halo headlight
Is anybody having trouble at high speed (around 55 mph) were the engine starts to sputter? Also, after changing to a 35 tooth rear sprocket I expected the DF should not have a problem going above 55 mph. Is that normal???
Sorry for the long post.
image.jpg
image.jpg

I have the same problem with my hoses for the secondary air system. I'm new to bike mechanics, so I was wondering how you went about closing it off and what any of the pros/cons of doing so might be.

Thanks
Tex

[axa]

Hello everyone,
First of all, I like to thank everyone for all the great info. The info provided by ya has fixed some of the problems i had. Thank you guys. I bought my 2012 DF250 RTB-A from Killer Motorsports at the end of June and received the DF in the middle of July. Since then, I have not received my papers to register the DF. I regret buying from Killer Motorsport as they customer service sucks a$$.
Anyways, my problem with the DF is that I can't seem to get pass 55mp without the engine sputtering or choking, or it seem as it is cutting out.
When I first got the DF, it felt as the riding was heavy and it picked speed slow. But after reading this great forum, I adjusted the valve on the crank and the DF became better. The valves had no gap what so ever.
Here is a list of mods I have done to my DF:
- close out the secondary air system ( as it kept busting the hose)
- change the stock swear sprocket to a 35 tooth
- added a 108 main jet, and the mechanic did something to the pilot jet where it acts as a 45 pilot jet
- added 3 washers to the needle jet
- tried a reverse air ram with the new filter I bought on eBay. ( I will post that air filter pic soon) the reverse air ram didn't work as I was going 35-40 mph the engine would just die out. Put the stock filter back on and the engine did a lot of sputtering around 40 mph. So, I tried this other filter I ordered on eBay that looked similar to our stock air filter except it has a plate cover on top of the air filter. That filter resulted a smoother ride till the problem I'm having around 55 mph.
- changed all turn signals to led, along with a new led halo headlight
Is anybody having trouble at high speed (around 55 mph) were the engine starts to sputter? Also, after changing to a 35 tooth rear sprocket I expected the DF should not have a problem going above 55 mph. Is that normal???
Sorry for the long post.
image.jpg
image.jpg

the sputter at top end is common and this bike has a top speed on a flat of about what your getting.
the sputter has proved to be a slight starvation for air at top speed. for me doing the reversed air ram with the stock filter was enough to fix it.
barone had tried taking the filter off completely witch temporarily fixes the issue.
another has tried a filter that allows more air flow.

Apparently that air scoop you bought forces way too much air even at moderate speeds.
it would be interesting to know if you could apply partial choke with that scoop on reversed and see what top rpm/speed is attainable.

[Chi town]

I have the same problem with my hoses for the secondary air system. I'm new to bike mechanics, so I was wondering how you went about closing it off and what any of the pros/cons of doing so might be.

Thanks
Tex

image.jpg
What my mechanic did was cut the hose with the bracket that came from the engine block. He cut off half the metal nipple and welded it shut.
The left side of the pic, he just cover it with a plug that you can get at any parts store..
Hopes that help

[axa]

I have the same problem with my hoses for the secondary air system. I'm new to bike mechanics, so I was wondering how you went about closing it off and what any of the pros/cons of doing so might be.

Thanks
Tex

Closing it off has now on several occasions proven to prevent it from blowing out.
I think its necessary unless you find a braided or metal replacement.
That said the system is not needed.
You may get an increase in backfire without it, but who cares.
Ive found increasing your airflow almost eliminates the backfire.

[barnone]

Chi town and Tex,
You guys need to do a little searching and reading for answers to your questions. All have been discussed many times in this thread.

Chi town,
I have the sputtering problem and need a less restrictive air filter. Take you air cleaner off for a test run. When I did that, DF ran up to 7500 RPM with no sputtering.

Tex,
There is a lot of threads about removing the AIS. Take it all off, put a cap on the vacuum port on the intake, and make a plate out of aluminum to seal off the port on the engine.

[Chi town]

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

[Chi town]

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]

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?