Wide open throttle Question

georgeknight

New Member
Sep 26, 2008
34
0
0
65
Lebanon, Mo.
I have a 80cc china girl. I've ported the exhaust to match my expansion chamber. It made a world of difference. But I notice when I get it to WOT the engine seems to studder. Could it be needing more fuel. It did this with the stock pipe too. I could open the jet up a little. I saw something about this posted on here but having trouble finding that post.


George
 

Ghost0

New Member
Mar 7, 2008
764
0
0
Bellingham, WA
What expansion chamber did you use?

First thing I would check is your plug. The pipe and mods have probably altered your effective air fuel ratio. Some have had to richen their mixture and some have had to lean their mixture. Only the plug will tell you for sure. To check your plug:
Get you engine to operating temperature.
Make a full throttle run of between 1/8 and 1/4 mile.
Hit the kill switch and pull your clutch lever.
Once stopped let the engine cool and check your plug.
Adjust jetting and needle settings as necessary.

I had to lean mine out quite a bit. I am running a .025 inch jet and the clip on the highest (leanest setting), but that is how mine is. Only reading your plug will tell you where you need to go.
 

Ghost0

New Member
Mar 7, 2008
764
0
0
Bellingham, WA
That is the same one I used too. Follow the steps for checking the plug and then work on adjusting your pipe. Your header length, distance from exhaust gasket to start of your expansion chamber should be around 12 inches to start, longer for more torque, shorter for more top end. Get your jetting correct first.
 

captainrichhill

New Member
May 31, 2008
203
0
0
Well I've had the same issue on mine. It's gotten cooler here. It's about 50 and I wasn't getting 22-24 mph at WOT. That's about 6 mph slower then normal. I tried to figure if I was rich or lean.
I added the choke and that just slowed it down more. I then turned off the fuel and within 5-10 seconds the speed increased dramtically. I was going over 31mph. The next ride I really worked the fuel shutoff valve to get it just right and man does it run now. I saw 34-35mph at one point.
My question is this:
Do I have one of those "bad" tapered needles??? Another thread mentioned that the taper was wrong on some of these carbs. However, the carb at WOT doesn't use the taper, the jet orafice meters the fuel.
Any ideas???
 

Ghost0

New Member
Mar 7, 2008
764
0
0
Bellingham, WA
You will need to rejet your carb. Simple to do with a soldering iron and the correct drills. Here is where I got mine. 25pc. Carburetor Drill Kit
It is odd that the colder weather made it go rich. Usually the cooler denser air will make it go lean. Maybe it was rich all along but the higher ambient helped vaporize the fuel better.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,827
764
113
Los Angeles, CA.
What I did was go to my LHWS with the jet, & found a jewelers drill bit that was the same size as the jet... then I bought the next 6 smaller size drill bits for $1.00 each.
Then I did the soldering trick!
 
Last edited: