Dong Fang DF 250 RTB Bobber Information

[GonzoX]

Wow that's odd A_Pilot,

Mine sputters as well. And carburators scare the crap out of me. My brother who knows bikes (not the one that broke mine) told me as long as it runs just leave it alone so I will do that for now. Mine does not stall like yours does but it does sputter. Its more of a spit sound or pop sound coming from the carb. Wish I knew. The exhasust sputtering on downshifting and deceleration is normal I have read but not sure about the sputtering. When it does this I can feel my whole bike jump a bit. It's almost like there was an air bubble in the fuel line. Starting to wonder if it may be a gas cap issue. That's one thing I am glad I dont have like others, a leaky gas tank. But then again, only had the bike a month or so.

If you havent already, read the whole thread. Lots of info here. Many here have swapped out jets on the carb because by default this bike is set up to run lean. Im guessing that causes 90% of the problems here. I have yet to get my bike up to 50mph so I cant say if it stalls at that speed yet. I am still breaking it in. Fastet Ive run it was 40mph.

And yes the shift rod issue seems to be common. Not even sure I want to ride my bike again until I get a spare but I did get my original one repaired so that will get her back home where she belongs. Hope mine doest take two months to get here. Took a month to get my bike. Now you have me worried.

Here is a pic of the repair work they did on mine. I still need to get some spare nuts to brace it more.
Fort Hood-20120530-00015.jpg

BTW I do remember reading something on the killermotorsports web page about stalling out. It was on one of their maintenance sections. Maybe you could look there or just do a google search. I hope you figure it out because that would help me and a lot of other newbs out as well.

I hope you figure it out. I will be watching your post and as always I follow this thread like a hawk at least once a day. It's a gold mine for DF owners.

[A_Pilot]

I could tear into the carbs, i just hate major engine repair, what size carbs would you recomend? And or where can i get them?

[GonzoX]

Dont know enough about them to comment but there are many posts here in this thread about getting jets sized 100 or 105 IIRC. You can do a thread search on carbs or jets to get that info. Seems they have had a lot of luck doing that.

[mrepooh]

Hello all;
i have had my DF Bobber about 3 months, like the slow ride easy & light turning or the bike. I cannot for the life of me figure out why after throttle around 60MPH and fully warmed up the bike sputters then stalls i have to pull off the road. i am guessing either vapor lock, or because of gravity fed gasoline and too much shaking?? i am lost on that subject. ANY ADVISE? also very steep hills in 3rd gear (40mph) she will stall as well..
attempted: higher idle to keep gasoline "chugging", less restricting air filter,slower deceleration. i am out of ideas.
2nd my shift rod Broke in the SAME location! must be a weakness in manufacturing. called in 2+ months ago for my replacment shifter rod(still not here) luckily i have metal working connections, just be carefull the threads are REVERSED towards the acutal trans, (for safety)
the running light is a little dull but riding with one light on BRight is good enough...
i do love the bike just wish i could ride it on local 55 MHP highways with out stalling.

Sounds like you're running lean, I had the same problem when I removed all the secondary air injection components. I did not block off the vacuum port on the carb plenum that was connected to the EGR, causing a large leak of air. When I blocked the air out I had to retune the carb's fuel mix, ours is located near the bowl mount facing down, on the engine side, if you screw it closed you will shut fuel supply and vise versa. In my case I had to back off the fuel supply to the engine.

The first thing I would do is check for leaks, have you modified the emissions component? My issues where broad, before tuning the fuel mix I stalled at idle, at constant speed, and at deceleration... If there's no leak close your fuel mix valve.

[mrepooh]

Wow that's odd A_Pilot,

Mine sputters as well. And carburators scare the crap out of me. My brother who knows bikes (not the one that broke mine) told me as long as it runs just leave it alone so I will do that for now. Mine does not stall like yours does but it does sputter. Its more of a spit sound or pop sound coming from the carb. Wish I knew. The exhasust sputtering on downshifting and deceleration is normal I have read but not sure about the sputtering. .

This is a classic symptom of running lean, you can thank all those nice EPA components. I thank the lord the State of Nevada does not sniff motorcyles. Any who, you can thank Barone for this:

http://docs7.chomikuj.pl/603318020,0...ing-Manual.pdf

This link does not have a complete copy of the manual, if you want one message me and I'll email it to you.

Yank all of the EPA junk out, plug up the plenum vacuum port, and retune your carb, it makes a world of a difference in the how it feels across the powerband; I can't say it's faster, but much smoother operation and better cold starts.

[DanDaMan]

indeed anyone wanting/expecting the bike to run well past 3/4 throttle needs to upgrade there jets , at the very least the main jet ( I jumped mine to 111 and I still "lean out" when aproaching 80 mph indicated (but I also have a modified air ram) , gunna put a larger needle jet in to see how much that helps )

then after u rejet as stated above "retune the carb" , I stuck a small screw driver in my back pocket , screwed my fuel mix all the way in then back out 2 turns then rode her , stopping when acted up and backed it out 1/2 a turn more/repeated as needed till got to the sweet spot where backing it out didnt help no more then turned it back 1/2 a turn and rode her a thousand miles

ps , fuel mix screw is front of carb facing front tire , idle is on side

anyone within 60-100 miles of austin tx , I be willing to help out (long as not cold or rainy) can even come to you , although if road tuning u need another bike to ride along with me as mine has been heavily modified to fit my 6'5" frame and not met another man yet that can reach my shifter or foot brake :p ( just finishing my stereo instalation 150 watt amp into 2-8" speakers mounted on sissy bar :p )

[A_Pilot]

This is a classic symptom of running lean, you can thank all those nice EPA components. I thank the lord the State of Nevada does not sniff motorcyles. Any who, you can thank Barone for this:

http://docs7.chomikuj.pl/603318020,0...ing-Manual.pdf

This link does not have a complete copy of the manual, if you want one message me and I'll email it to you.

Yank all of the EPA junk out, plug up the plenum vacuum port, and retune your carb, it makes a world of a difference in the how it feels across the powerband; I can't say it's faster, but much smoother operation and better cold starts.

Is the "plenum vacuum port" the tube connecting to the engine itself?

[DanDaMan]

hmmm , isnt it the hose connection on the intake manifold (black bit that bolts carb to motor)

anyways its an easy deleat - small pipe to side of motor with hose attached remove and plug ( I used sheet metal between motor and pipe , bolt up and remove to make sure didnt puncture (my 1st try I punctured sheet metal and it leaked) reinstall ) (or just plug the pipe) , unplug hose from intake manifold to the air injector and plug , unscrew air injector from front bracket toss onto work bench , ride till tires fall off

[mrepooh]

Is the "plenum vacuum port" the tube connecting to the engine itself?

Correct, it's that black piece of plastic (connecting the carb to the engine) that has a tiny 1/4 or 5/16 diameter brass flange port and hose attached to it. You might want to check that for leaks if your stock everything is buttoned up properly. If you removed all your emissions components you're gonna need to plug it and cut the fuel mix to the carb.

If everything is all good and you're still having problems, as Dan states, you're going to need to increase your main jet. Altitude plays a huge role in the main jet's performance at open throttle, here in Vegas we're 4000-6000 ft above sea level, I won't benefit much from a larger main jet, the stock 105 I have is good enough. But for low altitude areas you might want to up the jet to at least 110 if you're planing to haul @$$.

When ever I roll around I have a small bag of tools around, I've had so many problems with this bike I've fixed I feel like I'm in the Navy again fixing SH-60B seahawks LOL.

If you can possibly post a vid that would help out a lot :] Troubleshooting on the net can be a b**ch.

[mrepooh]

hmmm , isnt it the hose connection on the intake manifold (black bit that bolts carb to motor)

You're right, I've always referred to single vacuum chambers as plenum and multiple vac chambers as manifolds :]