JH600 stalling

[milton]

A couple of weeks ago Milton posted about this subject, noting a thread in a Chinese forum in which a JH600 owner found that a key electrical spring connection between the ECU and wiring harness had become corroded. Once he soldered the connections his stalling problems were resolved.

Wonder if anyone else has tinkered with those connections?

cheers

1. Compression pressure low; faulty decompression valve
2. Vacuum leak in intake manifold
3. Spark plug wire worn or faulty
4. Fuel pump pressure low, due to worn/faulty part
5. Fuel jet worn/faulty/dirty
6. Idle speed actuator worn/faulty
7. Throttle position sensor worn/faulty
8. Manifold absolute pressure sensor worn/faulty
9. Coolant temperature sensor worn/faulty
10. Bad wire contacts, spark plug, etc.
11. Bad fuel, bad fuel filter, junks in the fuel line

This is a list of possible symptoms and causes for JH600 engine stalling, complied by a Jialing owner (Xiao Zhang in Shanghai) based on materials gleaned from the Chinese Jialing manuals and translated by me. As we can see, there are a large number of possible (official too) causes to the problem and there is no single point of failure that can be identified as the sole culprit. However, with this list and what Eric has suggested about the fuel mixture being too lean, I have gradually formed my opinion about this tough problem. I believe that the lean fuel mixture compresses the “margin of error” for all the components involved and makes the ECU highly unreliable. In other word, the ECU is not robust enough and has very low tolerance to any aberrations coming from any of those sensors, leads, contacts, fuel lines, etc. Boosting the fuel mixture numbers on the right part of the “map” could be the silver bullet.

Now come back to the question asked by E. My latest struggle with my JH600 is as follows (don’t laugh): On last Friday, I brought my bike to Xiao Zhang for a free fix for that “bad contact” problem I posted (from ECU plug to its circuit board). After that, the bike ran “seemingly” better for a short 10 minutes (although made no difference on the stalling) then started to exhibit some hesitation whenever the engine reaches 4000 to 5000 rpm (almost like what I experienced last time with bad fuel). Xiao Zhang happens to have a “spare” manifold pressure sensor handy, so we pull it out and replaced that. Then he thought my spark plug NGK cr7eix is not the correct part and replaced it with his used cr8eix too. After this 2 new components installed, my bike started to give me the worst ever performance with incessant stalls, rough idling and epic backfires. Now it sits in the parking basement waiting for the idle speed actuator, which is not readily available from the Bosch distributor. Those parts are not super expensive and new parts are “usually better” than old parts, which is why I let him, or me rather, to go down this wholesale parts replacement path. If the idle speed actuator does not bring the bike back to life, I’d have him reverse some of the steps and see if any one of the steps is causing my new problems. If that doesn’t work, I am going back to Dr. Cui.

Summary: the tinkering and soldering did not bring my bike any closer to the resolution of the problem. It might have helped, but I just don't know any more.