Honda GCV 520 Engine Firing on Single Cylinder - Confusing diagnostics

[MikeDH]

Hi all
I have a Honda GCV 520 two cylinder V engine powering my Countax mower but is only firing on a single cylinder. I have carried out initial diagnostics but the results leave me totally confused. I have summarised the actions taken and results below. The engine runs, as expected lumpy with one cylinder firing. I changed the petrol filter and both spark plugs to no avail.

1. Remove 'LH' coil kill input from diode - no effect
2. Remove 'RH' coil kill input from diode - no effect.
3. Remove 'LH' HT lead from plug - Engine Stops - HT therefore seems OK?
4. Remove 'RH' HT lead from plug - Engine Runs
5. Swapped 'LH' and 'RH' ignition coils thinking one could be faulty - same results - coil which appears OK on the 'RH' cylinder does not rectify fault on the 'LH'?
6. Checked valve clearance on 'RH' - c0.007" which seems OK
7. Spark seems weak on the cylinder which is not firing but surely it will fire with even a weakish spark.
8. Checked the airgap between the ignition coil cores and the flywheel
9. LH plug clean, RH plug little 'wet' when removed and inspected

So I am at a loss whether I still may have a HT problem or a cylinder problem. Hope you can give some ideas - I still think it is a HT / Ignition problem
Many thanks
Mike


7

 

[bertsmobile1]

Pull both of the kill wires off the coil and see what happens

 

[cpurvis]

Check to see if the valves on RH cylinder are both opening and closing.

 

[MikeDH]

Hi. Thanks for your reply. With the two kill leads connected (at the coil modules), there is no change in the engine performance. You need to attach the kill wire on the running cylinder to stop the machine. The rev counter now shows interestingly '0000' rpm! Now, since one plug is wet and the other dry I am going to focus on the carb - taking the twin port carb off, stripping it and cleaning parts with carb / ultrasonic cleaner. I will report back on the forum in 1-2 days. Again, thanks for your suggestion.

 

[MikeDH]

Incidentally, thanks to second post too. Yes, checked earlier - valves on RH cylinder open and close OK. Thanks