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Post by hudsonjames2013 on Aug 14, 2016 15:13:55 GMT -5
Hi I got a sukida sportsman 2 125 scooter put a sports exhaust on it and it was running fine last week and I left it for a day and the day after I rode it and when I decelerate when I'm slowing down my exhaust backfires everytime I slow down can someone help me please
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Post by flyangler on Aug 14, 2016 15:36:13 GMT -5
Sounds like a lean back fire did you upjet when you put the sport exhaust on?
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New Rider
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Post by hudsonjames2013 on Aug 14, 2016 16:23:26 GMT -5
I'm sorry I'm a newbie lol what does upjet mean mate and I know about the air/fuel mixture screw but which way do I screw it to turn to rich will that sort through backfiring about a week ago it was all sweet no problems or backfiring at all untill one day I rode it and when I was slowing down it backfires
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New Rider
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Joined: Aug 14, 2016 14:29:13 GMT -5
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Post by hudsonjames2013 on Aug 14, 2016 16:24:24 GMT -5
And now when I ride it and keep slowing down it backfires from the exhaust
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Post by wheelbender6 on Aug 14, 2016 20:39:05 GMT -5
I agree that you need to try a bigger jet. They are cheap. A way to confirm that is look at your spark plug. If the insulator looks white, rather than tan, you need a bigger jet in the carb.
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Post by oldchopperguy on Aug 14, 2016 22:02:28 GMT -5
Welcome to the site!
It does sound like you may be running lean. Do as wheelbender6 recommends and you can see by the sparkplug condition. The fact that it ran OK at first is puzzling. It is possible with a very low-restriction exhaust that it will pop some upon deceleration.
If your plug shows that nice tan color, you may have to try some other things. If the plug is too white, you will need to install a richer jet. These carbs usually have a low, and high-speed jet. Usually only the high-speed jet needs to be changed. Getting the carb just right sometimes requires quite a bit of tuning.
Keep us posted and if you can't get it right, somebody here will surely be able to help.
Ride safe,
Leo in Texas
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Post by hillbillybob on Aug 18, 2016 4:45:00 GMT -5
An air leak in the exhaust system will cause some popping when decelerating. Something as simple as a clamp not being tight enough.
I'd also check the vacuum line to the air cut valve on the right side of the carburetor. The whole purpose of that valve is to prevent exactly what you are describing. If it doesn't have a good source of vacuum, it doesn't work.
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Post by urbanmadness on Aug 18, 2016 13:28:00 GMT -5
Things to check. 1. too small a main jet, 2. vacuum cut off, 3. vacuum leak. Did you make other changes besides the exhuast? IE a pod air cleaner? Exhaust nuts tight with a new gasket?
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Post by JerryScript on Aug 18, 2016 13:41:43 GMT -5
You should also check the carb's decelerator pump, if it has one. Most 125cc and larger carbs have a decelerator pump on the side. It's purpose is to add a bit more fuel when releasing the throttle to compensate for the loss of vacuum that occurs at that time. If the decelerator pump diaphragm is dried or torn, it won't function properly.
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Post by wheelbender6 on Aug 21, 2016 9:12:48 GMT -5
I was searching on some jetting info and ran across this article about exhaust backfire. A half turn on the pilot valve may help if your main jet is the proper size and there are no air leaks in the exhaust: "this normally occurs because the pilot mixture is too lean, rather than overly rich. Here's what happens, lean mixtures tend to burn slowly, and incompletely, so when the throttle is suddenly shut at road speeds combustion is incomplete, the pilot jet is just too small to supply enough fuel under those conditions. The unburned fuel flows out the exhaust valve where the hot exhaust pipe ignites it with a bang. Nine times out of ten all it takes to cure the problem is a slight richening of the pilot circuit, if your bike has a carburetor(s) a half turn richer on the pilot screw should do it. If you've got EFI go one step richer on the low speed screw of the module, you did install a "cheater" (adjustable EFI) module didn't you?
Other things that can cause an after fire on deceleration include exhaust system leaks, leaking air injection systems, vacuum leaks or anything that allows combustion supporting fresh air to enter the exhaust system when the throttle is closed."www.motorcyclecruiser.com/pipes-jets-problems-solutions-how-to |
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