Please help df250rtb

Blr3a · 07-27-2019, 03:30 PM

First time poster out of desperation. Picked up this project and love the bike. It sat in the weather for some time by previous owner and I’ve had to repair or replace a lot on the bike.

Old carb was eroded too bad to repair so I replaced it. New spark plug, coated fuel tank, new filter and lines, etc. It starts right up, idles like new, revs to half throttle great. After installing and adjusting a new clutch cable it shifts great through the gears.

Problem: it has a terrible miss above about half throttle. Maybe 4K rpms (guessing). If I shift when it starts to miss I can roll into fifth and it will go about 40-43mph and that’s it, it’s just sputtering and popping. Back down to 38moh and I could ride all day with no sputtering and popping. New carb, float seems to be set right, air screw adjust makes no improvement at all. Thought maybe valve adjustment. The exhaust valve was tight so I set it to slide .006 and hold .008. Seemed to smooth the idle a tad but made no difference in misfire or backfire. I’m at a loss, don’t know where to look next. Shooting from the hip maybe: coil, stator, cdi? Maybe burnt valve, but I don’t really know how to check or diagnose? Any ideas? Here’s a video:

Stretch-N-Poke · 07-27-2019, 05:54 PM

I have a bike that keeps eating Voltage regulators. It does this every time one goes bad. What happens, is when the regulator/rectifier starts going bad, it cant handle the higher voltage at higher rpm, and causes it to not send enough voltage to the coil, and causes it to miss. This may not be the problem with your bike, but for $12, its worth a shot.

culcune · 07-28-2019, 01:26 AM

Try getting hold of member Bar None. He has a Dong Fang now (their café bike) and used to have a couple of bobbers. In fact, on Mychinamoto which is another forum dealing with Chinese bikes but mainly for ex-pats from Europe and elsewhere living and working in China, but the longest thread was started by him and his bobber. There are active members there (Bar None pops in from time to time since his café bike uses the same engine anyway).

LOL--I was going to link the thread, but you already asked there...

Weldangrind · 07-28-2019, 01:46 PM

Welcome!
What type of replacement carb did you get? Does it have grooves in the jet needle (within the slider) to allow changing the height? If so, move the clip down a notch and see if it improves.

Blr3a · 07-28-2019, 10:35 PM

Quote:

Originally Posted by Stretch-N-Poke

I have a bike that keeps eating Voltage regulators. It does this every time one goes bad. What happens, is when the regulator/rectifier starts going bad, it cant handle the higher voltage at higher rpm, and causes it to not send enough voltage to the coil, and causes it to miss. This may not be the problem with your bike, but for $12, its worth a shot.

Haven’t really considered that. The one on the bike is pretty weathered anyways, I’ll order it, a coil, and cdi from amazon since they’re so inexpensive.

Blr3a · 07-28-2019, 10:37 PM

Quote:

Originally Posted by culcune

Try getting hold of member Bar None. He has a Dong Fang now (their café bike) and used to have a couple of bobbers. In fact, on Mychinamoto which is another forum dealing with Chinese bikes but mainly for ex-pats from Europe and elsewhere living and working in China, but the longest thread was started by him and his bobber. There are active members there (Bar None pops in from time to time since his café bike uses the same engine anyway).

LOL--I was going to link the thread, but you already asked there...

Thanks. Yea I asked there as well, I’ve had at least a hundred projects through my garage over the years... and I’ve given up on some due to costs outweighing value upon completion... but I love the way this bike rides and I won’t give up on it. I’m desperate. Never seen an issue similar to this one

Blr3a · 07-28-2019, 10:39 PM

Quote:

Originally Posted by Weldangrind

Welcome!
What type of replacement carb did you get? Does it have grooves in the jet needle (within the slider) to allow changing the height? If so, move the clip down a notch and see if it improves.

It’s an exact replica of the PZ30 that was on it. Even down the 88 jet. eBay $26. I haven’t checked the needle but I could try that and add a washer or two to try if it doesn’t have grooves.

Thanks

Weldangrind · 07-29-2019, 11:14 AM

There a few reasons that I prefer a Mikuni; the bowl screws aren't tamper-proof, the pilot mixture screw isn't tapped, the jet needle has five grooves and jets are really easy to find.

Blr3a · 07-30-2019, 05:18 PM

Quote:

Originally Posted by Stretch-N-Poke

I have a bike that keeps eating Voltage regulators. It does this every time one goes bad. What happens, is when the regulator/rectifier starts going bad, it cant handle the higher voltage at higher rpm, and causes it to not send enough voltage to the coil, and causes it to miss. This may not be the problem with your bike, but for $12, its worth a shot.

Man... I can’t thank you enough. Of all the electronic components, the rectifier was about the last thing I figured it could be. It came in today and I tried it first, runs like brand new. Can’t believe it. No misses or pops. Now I have a spare cdi and coil I guess, but at $8 a piece I’m ok with that. I was about ready to pull the head.

Stretch-N-Poke · 07-30-2019, 08:35 PM

Quote:

Originally Posted by Blr3a

Man... I can’t thank you enough. Of all the electronic components, the rectifier was about the last thing I figured it could be. It came in today and I tried it first, runs like brand new. Can’t believe it. No misses or pops. Now I have a spare cdi and coil I guess, but at $8 a piece I’m ok with that. I was about ready to pull the head.

Glad it got you all fixed up brother. Electrical parts are cheap. I try to keep a few extras laying around. I was told that the reason my bike keeps eating rectifiers is because of crappy grounds on these chinese bikes. I added another, thicker guage, ground wire from a starter bolt to a bare spot on the frame. Havent had any problems since. But it hasnt been that long either.

Blr3a · 07-30-2019, 11:25 PM

Quote:

Originally Posted by Stretch-N-Poke

Glad it got you all fixed up brother. Electrical parts are cheap. I try to keep a few extras laying around. I was told that the reason my bike keeps eating rectifiers is because of crappy grounds on these chinese bikes. I added another, thicker guage, ground wire from a starter bolt to a bare spot on the frame. Havent had any problems since. But it hasnt been that long either.

I’ll keep that in mind. Thanks again!

NzBrakelathes · 07-31-2019, 04:45 AM

Quote:

Originally Posted by Blr3a

It’s an exact replica of the PZ30 that was on it. Even down the 88 jet. eBay $26. I haven’t checked the needle but I could try that and add a washer or two to try if it doesn’t have grooves.

Thanks

Here’s a good kit to undo the tamper proofing

https://rover.ebay.com/rover/0/0/0?m...2F303210680840

Makes it back to a normal carb n plenty options for jetting etc etc and mire

Blr3a · 07-31-2019, 07:11 AM

Quote:

Originally Posted by NzBrakelathes

Here’s a good kit to undo the tamper proofing

https://rover.ebay.com/rover/0/0/0?m...2F303210680840

Makes it back to a normal carb n plenty options for jetting etc etc and mire

My pz30 didn’t come with tamper prof screws. I already have a jet kit as well. Thanks though

07-27-2019, 03:30 PM	#1
Blr3a Join Date: Jul 2019 Posts: 7	Please help df250rtb First time poster out of desperation. Picked up this project and love the bike. It sat in the weather for some time by previous owner and I’ve had to repair or replace a lot on the bike. Old carb was eroded too bad to repair so I replaced it. New spark plug, coated fuel tank, new filter and lines, etc. It starts right up, idles like new, revs to half throttle great. After installing and adjusting a new clutch cable it shifts great through the gears. Problem: it has a terrible miss above about half throttle. Maybe 4K rpms (guessing). If I shift when it starts to miss I can roll into fifth and it will go about 40-43mph and that’s it, it’s just sputtering and popping. Back down to 38moh and I could ride all day with no sputtering and popping. New carb, float seems to be set right, air screw adjust makes no improvement at all. Thought maybe valve adjustment. The exhaust valve was tight so I set it to slide .006 and hold .008. Seemed to smooth the idle a tad but made no difference in misfire or backfire. I’m at a loss, don’t know where to look next. Shooting from the hip maybe: coil, stator, cdi? Maybe burnt valve, but I don’t really know how to check or diagnose? Any ideas? Here’s a video: Last edited by Blr3a; 07-27-2019 at 03:31 PM. Reason: Broken link
	1

07-28-2019, 01:26 AM	#3
culcune Join Date: May 2006 Location: Yuma, Arizona Posts: 9,056	Try getting hold of member Bar None. He has a Dong Fang now (their café bike) and used to have a couple of bobbers. In fact, on Mychinamoto which is another forum dealing with Chinese bikes but mainly for ex-pats from Europe and elsewhere living and working in China, but the longest thread was started by him and his bobber. There are active members there (Bar None pops in from time to time since his café bike uses the same engine anyway). LOL--I was going to link the thread, but you already asked there... __________________ "They say that life's a carousel, spinning fast you got to ride it well..." TGB Delivery Scooter 150 TMEC 200 Enduro--carcass is sadly rotting in the backyard
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07-28-2019, 01:46 PM	#4
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Welcome! What type of replacement carb did you get? Does it have grooves in the jet needle (within the slider) to allow changing the height? If so, move the clip down a notch and see if it improves. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
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07-29-2019, 11:14 AM	#8
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	There a few reasons that I prefer a Mikuni; the bowl screws aren't tamper-proof, the pilot mixture screw isn't tapped, the jet needle has five grooves and jets are really easy to find. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

07-27-2019, 05:54 PM	#2
Stretch-N-Poke Join Date: Jul 2019 Location: Chattanooga, TN Posts: 18	I have a bike that keeps eating Voltage regulators. It does this every time one goes bad. What happens, is when the regulator/rectifier starts going bad, it cant handle the higher voltage at higher rpm, and causes it to not send enough voltage to the coil, and causes it to miss. This may not be the problem with your bike, but for $12, its worth a shot.
	0