Honda XR125 L-4 3 month old battery, Bike has engine has started to die, exhaust goes pop (backfire?), engine cuts out all together, battery almost completely dead wont restart bike, starter just clicks quickly. A jump start from a car solves the problem immediately but keeps happening...... Any ideas?

Get the fueling set up on a rolling road. Honda set the fuelling to suit the Emissions and the Exhaust they fitted.An after market exhaust will usually have less backpressure and need a set up. When you say backfire, do you mean a great big bang or just a little popping sound from the exhaust? If it is the latter, it isn't a massive problem but a set up will cure it. A Big Bang could be a cause for concern as it means the ignition is taking place when the Exhaust valve is open and firing in the exhaust itself. This will give a drop in performance and may cause the engine and exhaust to fail.

I would check the jetting to be safe but it could also be dirt in the carb. The main jet has very little to do with lower engine speeds and especially idle. That is controlled more by the pilot jet and circuit. Your best clue is how it responds when you add more choke. If it gets worse then there is a rich condition but if it gets better then you have a lean condition. From what you have described it sounds like a lean condition.

When you let off on the gas on your bike, the fuel air mixture to the engine is extremely rich. So rich in fact that it will not burn. If your bike is backfiring through the exhaust with a loud pop, this is usually caused because your exhaust system has an air leak in it somewhere. Air is sucked into the exhaust system leaning out the fuel air mix and turning it into a combustable mixture which then ignites causing the pop. Check all the joints where the parts of your exhaust system come together.

Good Luck
steve

Backfiring on deceleration is air getting into the exhaust and igniting unburned fuel. You probably have an after market exhaust on. You need to seal up the exhaust system by replacing all the exhaust gaskets. Dig the copper crush washers out of the head and replace them with new copper crush washers. This should take care of most of the popping. If the problem persists,unbolt the fuel cut diaphragms from the side of the carburetors and inspect them for holes and stickiness. Replace the fuel cut diaphragms if they are bad . Fuel cut diaphragms are on almost all Honda Kei Hin carburetors to stop the cycles from popping or backfiring on deceleration With the stock exhaust.

sounds like no spark or little spark check the fule line make sure the petcock is not plugged

Two things can cause popping or backfiring on deceleration. The most common is air leaking into the exhaust through the exhaust pipe copper o-ring gaskets. This typically happens when the exhaust is replaced without removing the old ones (doubled up) or simply reusing the old gaskets and they don't seal. The other thing that can cause popping is bad air cut diaphragms on the carburetors. If they are old and sticky or have holes in them they don't properly shut off the gas on deceleration causing the backfire.

Most engines with cdi boxes have rev limiters. Popping or backfiring could also be caused by low back pressure (aftermarket muffler) and most commonly bad exhaust gaskets in the head.

Hi,

If you haven't put a new, properly charged battery already, do so.

Good Luck and Let me know,

Obe

You want to start with a valve adjustment, 0.004 ths, then set the timing, then the points at the high end 0.016 ths. this will create better voltage at the coils. Then sync the carbs last. It "MUST" be done in this order to achieve the best results. Ralan