Dong Fang DF 250 RTB Bobber Information

**Mixmaster** · 04-14-2013, 08:55 PM

Went for a big ride yesterday , beautiful Autumn day. Ran fine for most of it, then went for a ride on the motorway ( Highway) where its also ran fine at 70mph but then slowing back down to normal driving it began to stutter bad under acceleration. Any ideas? Its got the bigger main jet, at 38 spocket. Havent messed with the needle though

Cheers Matt

**Goodbar** · 04-14-2013, 10:18 PM

Originally Posted by Mixmaster

Went for a big ride yesterday , beautiful Autumn day. Ran fine for most of it, then went for a ride on the motorway ( Highway) where its also ran fine at 70mph but then slowing back down to normal driving it began to stutter bad under acceleration. Any ideas? Its got the bigger main jet, at 38 spocket. Havent messed with the needle though

Cheers Matt

Pull the plug and clean or replace and check for color
and or pull carb and run a jet cleaning wire thru both jets. sounds like a tiny piece of something is clogging a jet orifice. The high RPM maybe knocked a particle loose.

**DanDaMan** · 04-14-2013, 10:21 PM

start it , go wide open throttle and chop the kill switch and check your plug color , (better yet ride it untill its studdering and cut kill switch and check plug then)

and have a look at chain and air filter /choke

u using sparkplug that came with it ?

shuddering under acceleration makes me 1st think , leaking air intake manifold (the rubber bit that connects carb to the bike)

**freezerboy** · 04-15-2013, 01:08 AM

Can anyone who installed the 38t sprocket verify that you dont need to remove any chain links....and did the sprocket make much of a noticeable difference?

**DanDaMan** · 04-15-2013, 02:36 PM

i put on a 35 and needed to remove no link , but will need to , its at maximum adjustment back now , if it stretches even a bit im having to pull 2 links

speed change went from 55 top rpm top gear to shifting from 4th at 70 indicated into 5th as on "overdrive" or cruise gear

I also use a 428 chain to let me get larger front sprocket (17 tooth) stock bobber it 520 chain that cannot do this

42-35 = 7 teeth , and 15 to 17 front , 3 teeth rear or 1 forward = 10% speed change so , about 43% speed boost just from my sprocket change = geared for 79 mph indicated max rpms , but remember we have pushrod motors so it makes more power 1/3-1/4 below max rpms , I think my powerband is set for 70-72 max hp in 5th gear

ps - I have seen this bike hit my indicated top speed of 80 , but conditions had to be perfect , without help it just purrs along at 70

6'5" 175lbs - flat texas highways

a 38 tooth no front change , your looking at perhaps 62-65 mph indicated top speed a 35 would add another 6 mph to that

**chruk bashre** · 04-15-2013, 05:01 PM

**chruk bashre** · 04-15-2013, 05:41 PM

**Mixmaster** · 04-15-2013, 09:19 PM

Originally Posted by freezerboy

Can anyone who installed the 38t sprocket verify that you dont need to remove any chain links....and did the sprocket make much of a noticeable difference?

To me its definitely worth doing, the gearing is way better. Not sitting at 30mph in top gear

**Mixmaster** · 04-15-2013, 09:21 PM

Thanks Goodbar and Dan, yeah running factory plug. Will play around with all you suggestions and let you know how I get on

**freezerboy** · 04-16-2013, 02:48 AM

Thanks for all the input on the sprocket. I got a 38 i picked up from amazon a couple months ago that has a silver plating on which i am going to sandblast and paint black before i mount it. looking forward to this upgrade. Just hit 100 miles yesterday and the bikes running 100%. Got to change my oil now.

BTW, i ordered one of those electronic needle tachs from amazon and it arrived today. I plan to take the tank off in a week or two to repaint the bike and i will wire it up then. Ill keep ya all updated on how and if it works.