Dong Fang DF 250 RTB Bobber Information

[axa]

There's always going with a CV carb.Could help bottom end.Doubtful top end would get any better than the pumper carbs.

so is that what a vacuum carb does... not yet sure that would attain anything the shorter intake doesn't.
From what i gather, a shorter intake may help the low end by providing air that is available right there right now. While a longer or thinned out one may actually help with funneling and speeding up the air for help with top end.

since i currently need to run with the choke a bit (due to removing the intake manifold), i currently only attain 6.5k rpm tops. That last 5k is seemingly a big disadvantage limiting my top to no better than 55, indicated. The local town dump truck passed me on the way to work this morning.

[axa]

Continuing search for more ccs lead me to
http://www.aliexpress.com/store/prod...752848938.html
$130 shipped to USA
Asked vendor if it will fit the DF motor and what cc will it be.
Probably another wild goose chase.

The cylinder can be purchased separately and it has a 75mm od skirt so could stand some overbore if a larger piston can be found.
http://www.aliexpress.com/item/LONCI...079925191.html

Here is a 70mm piston.
http://www.aliexpress.com/item/70MM-...752380917.html

You might just go to your local auto place to get thin gasket sheet stock, then cut to your profile... i doubt a thin gasket is what you will be getting with pre-made.


That piston seems to be spot on, but id have too much reservation about those cylinder bodies, they seem to be quite off... and the description would have you believe they will fit everything, which i doubt.

If it were to just relocate mounting holes or making clearance for the rods, i wouldn't think too much of it. But i would fear there are other slight differences in how it lines up with the head, perhaps the matching head could be attained...
Also those intake ports seem to be way off as well, not sure that matters though.

So anyone have experience with aliexpress? seems to be alibabas' answer to ebay, but no better pricing.
I can get a replacement cylinder body for our bike for less than $40 delivered to my door. They want double those. maybe i cant compare, since i dont know if those are mass produced parts or not. though i suspect they might be are on atvs...

[ben2go]

so is that what a vacuum carb does... not yet sure that would attain anything the shorter intake doesn't.
From what i gather, a shorter intake may help the low end by providing air that is available right there right now. While a longer or thinned out one may actually help with funneling and speeding up the air for help with top end.

since i currently need to run with the choke a bit (due to removing the intake manifold), i currently only attain 6.5k rpm tops. That last 5k is seemingly a big disadvantage limiting my top to no better than 55, indicated. The local town dump truck passed me on the way to work this morning.

Instead of using an accelerator pump to add fuel,the carb meters fuel based solely on the vacuum signal from the engine and butterfly valve position.The slide is controlled by a spring instead of the throttle cable.If you're running with the choke on,your engine is running lean.

[axa]

If you're running with the choke on,your engine is running lean.

you don't say...



so anyway, today i started to do the retune.
Got lucky and a friend had an old keihin 99101-393 series main jet laying around...
It being way too big at 160 he gave me the idea, we filled it back in with copper solder, I then redrilled starting with a #56 bit.
Then my luck ran out... took it over to install when it slips through my fingers down the floor drain... that grate really should be finer...

Anyway a good tip if your looking to fine tune and have a set of number and metric drills.
He guessed he probably filled in and drilled out that same jet a few times since we were kids.
I would never have thought of it.

[axa]

This engine just seems to not have the same power at higher RPM as my 2010 DF had but that could be a faulty memory on my part. I did run 68 MPH GPS on my old DF and can only manage 65 MPH indicated on my 2012 DF with the about same gearing and the same jetting. That is probably only 60 MPH GPS as the speedometer appears to me to be off by 10%.

That much of a difference does seem a bit hard to explain.
Are you sure they were both 167fmm? As far as you know both from zongshen?
Did the old DF have the intake manifold?

I hope you are on to something with the air intake. I ordered a shorter intake off Ebay and will report on it when I test it.

Well i do suppose i maybe on to something, but i wouldn't have thought you would translate that into just shorting the port rather than eliminating it entirely.
So why insert another manifold at all? Perhaps you dont care to retap?
i can dig it.

And it was a bit of a pain as i did it with the head in place.
Also should have or make few specific tools like a short set of transfer punches. Normal length ones wont fit in the carb mounting holes.
As well a set of stubby drill bits... even my mechanics length were too long.
You could get away with jobbers if taking the head off though.

I will say removing the spacer does make adjusting the fuel mix screw a real bitch, but thats not something i plan to do often.

[barnone]

Both engine are 167fmm and look the same to me but what do I know.
Manifolds looks the same.


Anybody thought about the CDI being an issue? Like insufficient ignition advance at higher RPM?

I worked at a welding/machine shop as a kid but that was a few years ago. I'll try the short manifold while you do the no manifold deal.

Did you try cleaning up the inside of the stock manifold?

This looks nice. Have we identified these engines as Zongshen for sure?
http://www.chinascooterparts.com/sdp...t_for_ATV.html
1247402227.jpg

CY7004

Performance Cylinder Kit for ATV/Dirt bike 250CC engine (167FMM),include piston kit and gasket,change 67MM to 70MM, change 250CC to 300CC

[ben2go]

I wonder if there is a difference in cams or rocker arm ratio causing the lack of power compared to the 2010s.

[axa]

This looks nice. Have we identified these engines as Zongshen for sure?
http://www.chinascooterparts.com/sdp...t_for_ATV.html

CY7004

Performance Cylinder Kit for ATV/Dirt bike 250CC engine (167FMM),include piston kit and gasket,change 67MM to 70MM, change 250CC to 300CC

You know the problem is on these sites, they all use the same damn picture... with limited to no detail.
We will have to get some confirmation from the seller... thats if they even know, and thats if they care even to answer.

But it may well be a compatible zongshen, and i think we should inquire... you have, haven't you?

If we can confirm, and the price is within reason, im in for sure.

Anybody thought about the CDI being an issue? Like insufficient ignition advance at higher RPM?

it quickly passed my mind... there may well be science behind an upgrade, but i dont yet know what that would be...
I reckon Ill look into this if i start getting timing issues with the decked head.
In that case, ill be looking into an adjustable one.

But for now, since i read someone even on the heist site reported no benefit with a expensive CDI upgrade, those guys exaggerate everything, so my thoughts are elsewhere.

Did you try cleaning up the inside of the stock manifold?

This was though my first thought, the trouble on mine was as many voids in the rubber part as lumps. i think a putty fill would be required. A direct mount seemed actually less work at the time. If i cant balance the intake with jetting ill reexamine.

Anyway, sure its a valid test to try another length, a straight run would be best regardless. Who knows the tunneling just may be advantageous...

[axa]

This looks nice. Have we identified these engines as Zongshen for sure?
http://www.chinascooterparts.com/sdp...t_for_ATV.html

CY7004

Performance Cylinder Kit for ATV/Dirt bike 250CC engine (167FMM),include piston kit and gasket,change 67MM to 70MM, change 250CC to 300CC

This site has it too. A bit tough to read as their chart formatting was lost

http://www.ywsp.com/products/Perform...s-p460706.html

[axa]

Been studying different valve modification techniques... removing any the lip on the back of the valves left from the original machining process, seems to be a very popular adjustment. One site reported a 25% increase to flow on the engine they tested it with. A safe adjustment to make because it is not the part that makes contact with the valve seat (which is a related but separate modification entirely)

back cut.JPG

Thinning out and cleaning up the stems is a thought too.

I hope i find them nice and messy cuz I just love having any excuse to chuck something up in the lathe...
Though seeing how decent the head has been so far i don't anticipate much.


And how about this, anybody ever heard of power ringz?

ringz.JPG


“Why do such an idiotic thing?!?!?!?” you ask? All of the fuel entering the engine will bounce off the intake valve. It is rather hot since it just came out of a combustion cycle. The air will take the short-cut across the seat, and the heavier fuel elements in the intake charge will centrifugally slam against the back of the valve. These Powre Ringz will increase the surface area of the intake valve helping to vaporize more of the fuel. Some of the fuel droplets will hit the ridge of one of these Ringz and bounce off in several dozen smaller sized droplets. Some of the liquids will actually hit the valve and stick, radially thin out, then vaporize into the incoming air stream. Bottom line is liquid fuel doesn’t burn, and Powre Ringz will promote better vaporization.

Prepping Valves for Performance