NGK plugs dont stop, especially all at once, so there is another problem.
There are some resisters in the plug caps that can fail.
Are the plugs carbon fouling?(dry black) if so make sure the air filter is new, and oil is changed.
Does the enginge blow smoke or use oil?(wet black)oil fouled may mean rings.
Fuel fouled may mean the jettting is wrong or choke stuck open
Its the battery good(new) and charging ,put a multi meter across the terminals 12v stopped, 14v running approx.
it always helps to drain the carb bowls every few weeks
If exhaust is not standard, the jetting may be wrong.
does the fuel tap work correctly? only use the run or res positions never pri
A short in the kill switch or a worn ignition switch can cause a miss or backfire
While running it has a thump thump thump sound from the exhaust. Sounds like my subaru wrx. I thought it was a clogged fuel filter. But what happens is it seems two of the plugs go out when i makes that sound then the third plug goes out. The last two times i changed the plugs only #2 plug still has spark. The fuel filter comes apart and has 3/8" inlet and outlet which seems big to me.
Ok The new battery running flat may be the cause of the problem.
Try the volt meter across the terminals if it doesnt rise to around 14 v when the engine is revved, the alternator has a problem, they have an internal regulator .
I have seen these damaged when the bikes are jump started off another battery.
The plugs could be failing because of poor ignition voltage, if the battery is not charging
plugs 2\3 run off one coil, 1\4 of the other coil, so one coil probably fails first from the low voltage. It could also be a coil fault but it would be very unlucky for two coils to fail at the same time.
When you check for spark make certain the plugs are in the leads and are grounded to the engine, if the are not grounded the voltage rises in the coils and may cause damage
Drain the carb bowls with the small drain screw at the bottom of each carb bowl.
When i check the plugs i set them on the frame. They spark between the frame and nut of the plug but not the tip.
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the last set of plugs were black at the top 1/8" of the plug after two weeks. I oil is under 1000 miles the air filter is a few months old. The battery is new but needs charged once every two weeks. With new plugs it runs awesome. No carb work has been done recently. So i am doing to have that done. Also don't know how to clean the carb bowls.
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