Dong Fang DF 250 RTB Bobber Information

**Roadkill** · 06-12-2014, 11:44 AM

I'm running a Mikuni 30mm VM series. It's not a pumper so I just layed the extra bit of cable up under the tank. That did not solve the backfire issue so many of us have. I am running the stock jets. I have also replaced the CDI, coil, and plug with "hi performance" units. That did not help either. Just for the heck of it, I'm desiginig a signal conditioner for the line from the pulse coil to the CDI.

**barnone** · 06-12-2014, 12:03 PM

Originally Posted by Roadkill

I'm running a Mikuni 30mm VM series. It's not a pumper so I just layed the extra bit of cable up under the tank. That did not solve the backfire issue so many of us have. I am running the stock jets. I have also replaced the CDI, coil, and plug with "hi performance" units. That did not help either. Just for the heck of it, I'm desiginig a signal conditioner for the line from the pulse coil to the CDI.

I was not aware of a back fire problem that "so many of us have". I do not have a back fire problem on my 2012 DF.
Please describe this back fire problem.

**Roadkill** · 06-12-2014, 12:24 PM

Miss, backfire through carb, rough idle. Also at roll on and steady speed. Hot or cold. Load or no load. Since it came out of the case. 2012 Installed new fuel filter at PDI and changed at 50 mi. Bike has less than 100mi. I've seen several posts concerning carb problems. I did rejet the stock carb (110). Plug is tan like it should be. Not a mech so I'm guessing maybe valves - haven't checked them but will when I get a few more miles on her. Emmisions crap is gone and hole plugged. Did leave the crankcase breather on but it is exposed to the air as I installed a new air filter of about the same surface area.

**barnone** · 06-12-2014, 12:53 PM

Originally Posted by Roadkill

Miss, backfire through carb, rough idle. Also at roll on and steady speed. Hot or cold. Load or no load. Since it came out of the case. 2012 Installed new fuel filter at PDI and changed at 50 mi. Bike has less than 100mi. I've seen several posts concerning carb problems. I did rejet the stock carb (110). Plug is tan like it should be. Not a mech so I'm guessing maybe valves - haven't checked them but will when I get a few more miles on her. Emmisions crap is gone and hole plugged. Did leave the crankcase breather on but it is exposed to the air as I installed a new air filter of about the same surface area.

Neither of my two DFs had/have this problem you are describing. The stock DF should not be backfiring through the carb. Yep, there are a lot of posts considering carb problems, probably most caused by the owners.

I just fixed one I caused.

What model DF? How about adding it to your signature line?

Maybe an air leak causing the backfiring. Do you have good o rings on the carb manifold? Your DF should not need a 110 main jet. A 105 should be plenty big.

What was wrong with the stock carb and CDI,coil,etc? Don't just start changing parts out. I'd put it all back stock and start over.

**Roadkill** · 06-12-2014, 01:14 PM

This issue was there with the stock parts also. The CDI did seem to help power at mid to high range because of the 4 degree advance, I would say. I always install new ignition parts on new Chinese bikes and scooters. Probably a head trip, but I feel like the aftermarket parts are a little more reilable and they don't cost that much. I did reinstall the factory carb and main jet, CDI, and coil and nothing changed so I changed them back. As for the stock carb, I like the simplicity and quality of the Mikuni. Nothing got worse with the changes - power a little better. My next step is to squirt starter fluid at the manifold and carb connections. Just not sure what the stuff will do to the paint. I've heard some use WD40 for that test. It's a 2012 "B". Rear sprocket is 35T. Took out links to keep the fender clear of the tire. My back ground is electronic design and all the electronics stuffed into that little can with no sheilded wires bother me a little. Probably won't do much good but I still may look at cleaning up the line to the CDI input. Heck, it's a hobby.

**barnone** · 06-12-2014, 01:23 PM

All I can say is that my 2012 DF is all stock except for the rear sprocket change and air injection system removal and does not do the backfiring that you are describing.

**Roadkill** · 06-12-2014, 01:25 PM

I'll play with it awhile and post when I figure it out. Thanks for the input.

**DanDaMan** · 06-12-2014, 11:51 PM

ya sounds like u need to adjust your valves - baring a airleak

2010 dong 250 cha chopper 15-33 spockets car rear tire , 110 main jet - 90% highway use Austin tx
77 gs 750 susuki

so u did get another 1 Barnone ? awesome

**Roadkill** · 06-13-2014, 12:26 AM

Just found out that I blew out the plug I put in the emissions outlet that comes off the block. Repaired that and re tuned the carb. It's much improved but I still have the miss so I'll do the valves this weekend. .002 amd .004 if I remember correctly. I had a truck cut the corner and put me down so I'm also gonna change the oil just in case I had fuel leak into the oil sump while she was on her side. She was down for a min til they picked up the bike off of me. Some drivers forget what they're doing whe they see the bobber. Live in the DFW area so dumb drivers are the rule here. Loved Austin when I was there. Should have stayed.

**DanDaMan** · 06-14-2014, 08:14 AM

Originally Posted by Roadkill

Just found out that I blew out the plug I put in the emissions outlet that comes off the block. Repaired that and re tuned the carb. It's much improved but I still have the miss so I'll do the valves this weekend. .002 amd .004.

I do mine the same as my 74 Beetle air cooled pushrod engine, 6 and .008

and U do know the air injection itself is meant to "pop off" unspent fuel for cleaner emissions , - could that be the "miss" your hearing ?
many of us remove it and block it with homemade plate