Dong Fang DF 250 RTB Bobber Information

[Bobthebobber]

From my ex 2010 bike "Manual and sticker on frame both say .06mm intake and .08mm exhaust."
http://www.mychinamoto.com/forums/sh...rmation/page13
Better a little loose than too tight.


You need to check your valves ASAP. You can have engine damage if they are tight like mine were.
I had no clearance on mine when I uncrated the bike. Others here have also reported the same lack of clearance on their 2012s. You will suffer power loss if the valves don't close.

Plug looks like you are running too lean to me. I need to check mine as I went up to 108 main jet from my stock 105.

But adjust your valves before you ride any more. Get an experienced friend or independent shop to help you.

Okay ill check the valves this weekend. your 2012 had a 105 stock? What type of jets do these use because i have a bunch left over from a gy6 motor.

[barnone]

Okay ill check the valves this weekend. your 2012 had a 105 stock? What type of jets do these use because i have a bunch left over from a gy6 motor.

The carburetor is a PZ30 pumper.

[DanDaMan]

axa it helps a little , fresh air better n hot air , and at speed it actually does help a bit as a ram

[axa]

axa it helps a little , fresh air better n hot air , and at speed it actually does help a bit as a ram

Then i think i will try it but perhaps with a more of a wide horn type mouth though.
For i can see the principle applied as the speed increases the forced air flow will exceed the added resistance of a severely bent intake path.

But I cant justify doing this as a attempt to gain power by decreasing the temperature of the air.
Here is what i come up with:

Under no pressure (of course we have average pressure of about 30 milibars) the density of air per foot² at say an ambient temp of 70° is 0.075, even if in the back of the engine it is a sweltering 150° (which its not) the density then becomes 0.065
Which is an exaggerated increase of .010, then as oxygen is only about 21% of the air, that figure drops to a relative .002 density of oxygen per foot² of air sucked in...

Then as one cubic centimeter is 3.53146667 × 10^-5 cubic feet, 229cc engine = roughly .00808730046 cubic feet, it would take roughly 28,316 * 4 engine strokes to pass a single cubic foot.
at say 8000 rpm, that would be 2000 ignitions, so if im not mistaken 14 minutes to pass the air that would increase your oxygen by that squared .002 cubic feet.

I can go on with the calculations of how much energy is produced from this increase in oxygen, and then how that energy translates to movement of an object but i for one am already pretty convinced its entirely negligible.

So in doing this I can only estimate the increase in the volume of air, immensely outweighs any possible benefit of a reduction in temperature.
Perhaps if these intakes were under a closed hood or stiffled otherwise the benefit would multiply, but i just dont see it.

Can anyone suggest other variables that need to be taken into consideration in our set up?

[barnone]

Changed my oil for the second time at 204 miles. I added a magnetic drain plug (MDP) at the first oil change at 1.0 miles when the DF was delivered to me.

This is the amount of swarf that was collected on the MDP. The screen in the oil strainer was clean so the MDP is doing it's job.

BTW, this is typical of the amount of swarf collected on MDPs on almost all my vehicles at the first oil change after the MDP install. The amount decreases as time goes by on all.

[barnone]

I upgraded my carb jets. I'm now running a #108 main and a #45 pilot jet(slow jet) with the c-clip moved down one slot on my new adjustable needle. I did also get a #42 pilot in case the #45 was too much.
Will let you know how this works out.

KEIHIN ROUND MAIN JETS N424-36 NICKEL PLATED TO PREVENT CORROSION

KEIHIN SLOW JET N424-21

Carburetor Repair Kit - PZ-30


From the factory setup was #105 main and #40 pilot.

alleycat,
What jets did you end up with in your DF? Trying to prevent reinventing the wheel.
Thanks

[Bobthebobber]

The carburetor is a PZ30 pumper.

So from reading the manual... is it correct in saying that if I loosen the mixture screw it allows more gas into the carb? I brought it out about 2 turns and took it for a ride... hoping this will allow a richer mix. Got it to about 50-55 indicated on a long flat road. Still about 40-45 on any type incline and i blew my new hose. Will be replacing with a plate soon.


Should I try lowering the clip on the needle to raise it one notch? This carb does have an adjustable needle right?

[barnone]

So from reading the manual... is it correct in saying that if I loosen the mixture screw it allows more gas into the carb? I brought it out about 2 turns and took it for a ride... hoping this will allow a richer mix. Got it to about 50-55 indicated on a long flat road. Still about 40-45 on any type incline and i blew my new hose. Will be replacing with a plate soon.


Should I try lowering the clip on the needle to raise it one notch? This carb does have an adjustable needle right?

Good read at
http://www.jetsrus.com/FAQs/FAQ_reje...w_to_rejet.htm


The rejetting sequence
The order which provides the best performance is to change:
1) idle,
2) pilot screw
3) slow or pilot jet
4) main jet
5) the needle
6) accelerator pump (if equipped).
7) read the plug.

If I remember right you need to add washers to raise the needle.

[Gearhead45]

My new df, only 10 miles on her. image.jpg

[DanDaMan]

Attachment 12948my DF will do 80 , when the air temp is 45 degree's or so , and struggles to do 70 when its over 100 degree's , so yes temperature of intake air indeed makes a difference

negligable indeed , only a 12-15% speed increase from running colder air , but its the diff from cruising a highway and having to take the access road

I shift into 5th at about 68 indicated my ratio says I should float my valves at 85 , but I cant get but a hair over 80 in perfect yet very cold conditions

bob r u running stock sprocket ? that will make u top out at about 50-55 when your valves start to float making u unable to go faster