back fire

alonzo · 06-20-2008, 02:00 PM

hi yall,

Well lately lucy lu has been back firing comming down from a high rpm. usually I close the throttle at about 7,500 rpm to start slowing down and it will crack only once.

Is this a lean condition? do I need to start playing with the air/fuel screw again?

I tuned the screw with the throttle chop process. the plug was a light tan color like it should have been. I am not sure that I will be needing to mess with the mix anymore.
But Needing to make sure.

Am I going to have to break down and go get a bigger main jet for it?

What is the stock main jet sizing for the 2007 lifan gy5

Kawazacky · 06-20-2008, 02:14 PM

Mine does the exact same thing. I don't know why.

Check your engine case by the oil fill/dipstick for soot particles. The exhaust joint is right behind there, and it's possible an air leak there is the cause. But I don't really know.

warrior91 · 06-20-2008, 02:19 PM

leak at header/cyl junction???

mikaserla · 06-20-2008, 02:48 PM

Mine does that too. I thought it was normal.

IronFist · 06-20-2008, 03:35 PM

You might be lean, what color is your plug?

You can check for a manifold leak by sprayin a little wd40 on the rubber seal between the carb and the motor. The oil will leak in and seal any little crack. If the bike runs better for a few minutes then returns to the lean condition, that's a sure sign that the manifold isn't sealing correctly.

alonzo · 06-20-2008, 04:46 PM

I will check the manifold. today I tore off the header pipe and scored the rust off it. repainted it in high temp black sure hope it holds.

the header might have caused the pop, I clearly had a small leak because I saw where the soot was sneaking through the seals on both ends.

well I will keep my fingers crossed and have to see.

Thanks Fellas

TeamCheap · 06-20-2008, 05:27 PM

From what I have read that explains that popping when letting off the throttle is this.

With a small leak at the header pipe it allows air to be sucked in when engine braking and that combined with unburnt fuel that ignites on the hot header pipe causing the POP sound.

But thats just something I've read.

alonzo · 06-20-2008, 05:38 PM

after reassembling the machine I took the chance and started driving on the freshly dried header paint.

NO POP! I am thinking that it was the header/muffler connection.

and the paint is still on

By the way, can someone send me bruces' contact info? the ej cycles guy. I cant find his number anywhere.

IronFist · 06-20-2008, 06:53 PM

Quote:

Originally Posted by TeamCheap

From what I have read that explains that popping when letting off the throttle is this.

With a small leak at the header pipe it allows air to be sucked in when engine braking and that combined with unburnt fuel that ignites on the hot header pipe causing the POP sound.

But thats just something I've read.

T/C you smart cookie, you make a fortune.

Right on the money...again. :wink:
I think the air would be colder too, I heard that has something to do with it...

TeamCheap · 06-20-2008, 07:44 PM

Not so much smart as experienced.
I've had that exact same problem and after looking into it that is what I had read on it and a new header pipe gasket later problem was solved.

I still got a few extra gaskets just in case and I'll be using one on the wifes bike sooner or later.

Kawazacky · 06-20-2008, 08:05 PM

Did you use the XR200 or CRF230 gaskets, or did you use chinagaskets?

TeamCheap · 06-20-2008, 09:28 PM

XR200 gaskets.

katoranger · 06-20-2008, 09:31 PM

Bruce, 330-274-0098

Kawazacky · 06-20-2008, 09:36 PM

Any idea what year the gaskets were from? I'd hate to order XR200 gaskets for the wrong XR engine....but I'm betting gaskets from any 80s XR engine would work...?

Kawazacky · 06-20-2008, 09:37 PM

I'd like to give Bruce the business. but I sort of like to keep a working relationship with the local Honda shop. Anything I can get through them at a reasonable price, I will.

06-20-2008, 02:00 PM	#1
alonzo Join Date: May 2008 Posts: 527	back fire hi yall, Well lately lucy lu has been back firing comming down from a high rpm. usually I close the throttle at about 7,500 rpm to start slowing down and it will crack only once. Is this a lean condition? do I need to start playing with the air/fuel screw again? I tuned the screw with the throttle chop process. the plug was a light tan color like it should have been. I am not sure that I will be needing to mess with the mix anymore. But Needing to make sure. Am I going to have to break down and go get a bigger main jet for it? What is the stock main jet sizing for the 2007 lifan gy5 __________________ ALONZO 2007 Lifan a.k.a lucy lu. 2,000 miles of good riding.
	0

06-20-2008, 02:19 PM	#3
warrior91 Join Date: Nov 2007 Location: N.E. Saskatchewan, Canada Posts: 679	leak at header/cyl junction??? __________________ '91 Yamaha Warrior- stage 2 '83 Honda ATC 70 '08 Yongjiang 125cc mx (Loncin) '08 Yongjiang 150cc atv (Jinlong)
	0

06-20-2008, 05:38 PM	#8
alonzo Join Date: May 2008 Posts: 527	after reassembling the machine I took the chance and started driving on the freshly dried header paint. NO POP! I am thinking that it was the header/muffler connection. and the paint is still on By the way, can someone send me bruces' contact info? the ej cycles guy. I cant find his number anywhere. __________________ ALONZO 2007 Lifan a.k.a lucy lu. 2,000 miles of good riding.
	0

06-20-2008, 09:31 PM	#13
katoranger Join Date: May 2007 Location: Altamont, Kansas Posts: 15,103	Bruce, 330-274-0098 __________________ You meet the nicest people on a Honda Clone.
	0

06-20-2008, 02:14 PM	#2
Kawazacky Join Date: Mar 2008 Location: Saint John, N.B. Posts: 279	Mine does the exact same thing. I don't know why. Check your engine case by the oil fill/dipstick for soot particles. The exhaust joint is right behind there, and it's possible an air leak there is the cause. But I don't really know.
	0

06-20-2008, 02:48 PM	#4
mikaserla Join Date: May 2008 Posts: 18	Mine does that too. I thought it was normal.
	0

06-20-2008, 03:35 PM	#5
IronFist Join Date: Apr 2007 Location: Toronto Ontario Canada Posts: 2,585	You might be lean, what color is your plug? You can check for a manifold leak by sprayin a little wd40 on the rubber seal between the carb and the motor. The oil will leak in and seal any little crack. If the bike runs better for a few minutes then returns to the lean condition, that's a sure sign that the manifold isn't sealing correctly.
	0

06-20-2008, 04:46 PM	#6
alonzo Join Date: May 2008 Posts: 527	I will check the manifold. today I tore off the header pipe and scored the rust off it. repainted it in high temp black sure hope it holds. the header might have caused the pop, I clearly had a small leak because I saw where the soot was sneaking through the seals on both ends. well I will keep my fingers crossed and have to see. Thanks Fellas
	0

06-20-2008, 05:27 PM	#7
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	From what I have read that explains that popping when letting off the throttle is this. With a small leak at the header pipe it allows air to be sucked in when engine braking and that combined with unburnt fuel that ignites on the hot header pipe causing the POP sound. But thats just something I've read.
	0

06-20-2008, 07:44 PM	#10
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	Not so much smart as experienced. I've had that exact same problem and after looking into it that is what I had read on it and a new header pipe gasket later problem was solved. I still got a few extra gaskets just in case and I'll be using one on the wifes bike sooner or later.
	0

06-20-2008, 08:05 PM	#11
Kawazacky Join Date: Mar 2008 Location: Saint John, N.B. Posts: 279	Did you use the XR200 or CRF230 gaskets, or did you use chinagaskets?
	0

06-20-2008, 09:28 PM	#12
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	XR200 gaskets.
	0

06-20-2008, 09:36 PM	#14
Kawazacky Join Date: Mar 2008 Location: Saint John, N.B. Posts: 279	Any idea what year the gaskets were from? I'd hate to order XR200 gaskets for the wrong XR engine....but I'm betting gaskets from any 80s XR engine would work...?
	0

06-20-2008, 09:37 PM	#15
Kawazacky Join Date: Mar 2008 Location: Saint John, N.B. Posts: 279	I'd like to give Bruce the business. but I sort of like to keep a working relationship with the local Honda shop. Anything I can get through them at a reasonable price, I will.
	0