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Messages - Geiren

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General Discussion / Kymco 500. 24 Volt startmotor supply. Permanent solution for starting problems.
« on: April 18, 2025, 10:01:00 AM »
Hi, thought I would share my permanent solution on the starting problems with the Kymco 500 engine. Even though there are many posts about starting issues with the Kymco 500, none of them really offer a good long-term solution. I have a Kymco MXU 500, which has roughly the same engine as the Xciting, including the electrical system and starter motor.

The problem with the engine is that it lacks a decompression mechanism, which makes it difficult for the starter motor to turn the engine over fast enough.

What I’ve done is install an extra battery in series to supply the starter motor with 24 volts. This results in a completely different RPM on the starter motor, and the engine never has trouble starting.

Originally, the MXU comes with a battery the size of a YTX20HL-BS, with 310 CCA. I’ve installed two YTX14-BS sized batteries with 170 CCA each. It could probably work with smaller batteries to.

The only issue now is that only the battery connected to the engine’s 12V electrical system gets charged, while the extra battery has to be charged manually with a regular charger from time to time. This could probably be rewired with a DC/DC 12-24v charger, but the system can handle quite a few starts before the voltage drops low enough to risk damaging the battery.

There are some video explaining same solution on KTM bikes:

https://youtu.be/YU_bHsYLf4Y?si=5HzT3jjtgq3CKLhZ

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Technical | How To / 500ccm hard to start due to high compression
« on: June 23, 2024, 08:15:44 PM »
Hi, I hope someone can guide me in the right direction regarding my engine problem. There are several posts in this forum mentioning 500 engines being hard to crank, but I have not read any solutions for this problem. Assuming Kymco ATV, scooters etc. using the same engine or at least block, top etc.

I bought a 500 MXU (2009) with unknown engine problems a year ago. I split the engine and found a broken bearing for the balancing shaft. After replacing both bearings, I reassembled the engine while measuring every component inside the engine according to the workshop manual. Everything was according to spec. After some cranking, the engine started and was running smoothly.

The problem is the high compression in the engine, making it almost impossible to crank over. It sounds like the battery is flat and will only crank twice to the compression stroke. The recoil starter is impossible to use when the engine is cold, but once it’s warmed up I can start it with a small pull.

My understanding is that these engines only have a kickback decompression mechanism on the exhaust cam, so it doesn’t really do anything during the compression stroke.

So far, I have checked/replaced these things trying to get rid of the problem, but so far no luck:
- New battery
- Changed exhaust cam (The old was according to spec)
- New brushes in the starter motor
- Checked timing
- Connected 12V from a tractor directly to the starter motor

Any advice or suggestions would be greatly appreciated.

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