Dong Fang DF 250 RTB Bobber Information

I have a feeling the stalling bike has the size 86 main jet , FAR to small , causing it to over lean (fuel starvation) at speed , which if not corrected causes overheating and eventually valve burn

untill u get bigger main jet I think you need to RESTRICT (tape up) your intake not get a more free flowing one , take a 6" piece of duct tape rap it around your air filter only leaving it about 1/4 open , go for a ride if problem goes away thats the problem u need bigger jets (because your getting to much air in the air/fuel mix)


^^^^ messing with fuel mix screw could help also , If I recall screwing IN in richer and out is leaner , so try 1/2 a turn at a wack
PS - pay attention to how much you turn the screw so can get it set back to where it was originally (if needed) , by counting 1/2 turns made , write it down if need to



even with my big 111 main jet at 75-80 indicated the motor will occassionally cut out from fuel starvation but never bad enough I need to pull over


I went to auto parts store and bought a radiator hose (used the air filter for sizing) with a 180 degree bend in it cut it to only have the U shape bolted it to the carb the other end to the air filter , now I have a forward facing air intake out in the air stream - aka poormans air ram ( no real effect untill past 60 indicated )


its a fine line we ride on these small bikes , LEAN produces more horsepower thus more top speed , but to lean and you might as well toss a grenade into the motor

Quote:

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Originally Posted by DanDaMan

untill u get bigger main jet I think you need to RESTRICT (tape up) your intake not get a more free flowing one , take a 6" piece of duct tape rap it around your air filter only leaving it about 1/4 open , go for a ride if problem goes away thats the problem u need bigger jets (because your getting to much air in the air/fuel mix)

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Nice, I didn't even think of that. It's a whole lot better than running around half choked. There's no give with these tiny bikes, what you think is too little or too much become exponentially excessive once you get the bike going. You're right about the jets being too small, even in the high desert, 105 still seems to be running a bit lean once I pick up my RPMs.

Quote:

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Originally Posted by DanDaMan

I have a feeling the stalling bike has the size 86 main jet , FAR to small , causing it to over lean (fuel starvation) at speed , which if not corrected causes overheating and eventually valve burn

untill u get bigger main jet I think you need to RESTRICT (tape up) your intake not get a more free flowing one , take a 6" piece of duct tape rap it around your air filter only leaving it about 1/4 open , go for a ride if problem goes away thats the problem u need bigger jets (because your getting to much air in the air/fuel mix)


^^^^ messing with fuel mix screw could help also , If I recall screwing IN in richer and out is leaner , so try 1/2 a turn at a wack
PS - pay attention to how much you turn the screw so can get it set back to where it was originally (if needed) , by counting 1/2 turns made , write it down if need to



even with my big 111 main jet at 75-80 indicated the motor will occassionally cut out from fuel starvation but never bad enough I need to pull over


I went to auto parts store and bought a radiator hose (used the air filter for sizing) with a 180 degree bend in it cut it to only have the U shape bolted it to the carb the other end to the air filter , now I have a forward facing air intake out in the air stream - aka poormans air ram ( no real effect untill past 60 indicated )


its a fine line we ride on these small bikes , LEAN produces more horsepower thus more top speed , but to lean and you might as well toss a grenade into the motor

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That is an awesome idea!!!!! I am heading this weekend to get the bigger jets, should i replace the main and the other one? I think its called the pilot jet.i will repost a photo of the secondary vacuum to the left of gas tank (under it) for opinions.

ya I would , the pilot/slow jet while being the only jet operating at idle to 1/4 throttle does continue operating at wide open throttle

but you can do a "plug chop" yourself to see how well its running at low idle , start it up in nuetral speed the idle up a little let warm up and hit kill switch pull spark plug and check color , what u want is a nice "tan" spark plug (white is lean/black is rich) , myself I dont mine a slightly rich idle


if needed increase the slow jet , and jump the main to 110 or so , the rest can be coxed from the air/fuel screw to get you that nice tan plug

unless your gunna install an air ram then id go a bit bigger than 110


http://www.motorcyclecruiser.com/tec...n/viewall.html


ps - I mentioned be4 I used standard 10/40 oil , but could never find nuetral , well I messed with my clutch adjustment today and can now hit nuetral from both 1st and second without problems with engine running /wink


most here dont seem to use there bikes for "highway cruisers" but thats the very reason mine was purchased for ($3 for 70 mile trip or $8-10 for my GS750 for same trip ) , it rarely see's anything other than highway pavement , so slightly less tuned is ok for them

still looking for a 7 gallon harley "split tank" I can mount so's I can ride from austin tx to see my bro in N carolina , on 2 fill ups XD

I believe this is a first. Went for a short ride today and when I got back I noticed a funny smell. My horn bracket broke in half and the horn was dangling by the wires across the hot exhaust. I caught it before it burned thru but I'm going to have to fab a new bracket. Anyone else have that problem?

After reading all you guys problems maybe I got lucky. My bike needs to be warmed up whenever you start it cold but after that it runs like a dream. I have her wide open on the drive to work (speedo reading 70mph, with a 38 tooth rear sprocket) and she never stalls out in the least, just purrs like a kitten whether I'm going 7 or 70 mph. I never messed with taking the secondary air injection off, I just bought a silicone hose because the stock one would get brittle and blow out at highway speeds, since I put the silicone tube on the secondary air injection there has been no problems.

I had a bracket break - reflector across forks , just welded and bolted it back up

Man I really wish you guys had pictures of all this stuff. Where is the air injection hose etc and stuff like that. I was also looking for the richness screw and I just dont see it. I know its supposed to be towards the front wheel but I dont see it.

GonzoX: Here is a pic of the new hose I put on the secondary air injection. It is actually braided silicone hose used in home brewing of beer and wine, it can take much higher temps with out getting brittle and blowing out like the stock breather hose the bike comes with.Attachment 7430

gonzo - bottom left picture http://elescooterparts.com/parts/gas...Z26/PZ-26.html that brass srew showing is the fuel mix screw


and as pictured above the air injector has 1 hose going to it from the intake manifold (to make it pulse) , and 1 from the injector itself that takes those pulses and turns it into a bellows to push air into the exhaust cycle to have fresh air in the pipe to better burn excess polutants in the cat converter (sometimes resulting in some "popping")