I have a pressure washer with a 210cc Chonda GX200 clone that is very difficult to start. This article walks through the resolution.
Above is the equipment, it has less than 4h running time, so it is not ‘run-in’ yet, these type of engines improve up to 20-50h.
Spark
Spark was tested using a PET-4000 spark tester, all good.
Valve lash
Valve lash can make these engines hard to start, particularly excess lash on the exhaust valve reduced effectiveness of the compression relief mechanism.
There is no reason to think it is low on compression.
Valve lash was checked, exhaust was 0.15mm and adjusted to 0.2mm, inlet was 0.1mm and adjusted to 0.15mm. So, whilst they were low, the exhaust would give more compression relief… and not likely to be the cause of difficulty in starting when cold.
Interestingly, whilst diagnosing the problem, the starter rope broke, frayed about half way along. It was replaced with some 4mm paracord which was on hand, and some 4mm starter rope ordered in case the paracord fails. I will put it down to Chinese Quality rather than a defect in the engine at this stage.
Ignition / Spark
Spark plug looks good
Spark was tested using a PET-4000 spark tester, all good.
Above is the ‘secondary’ voltage of the ignition system at 3400RPM and moderately high load (being a pressure washer).
The spike is not fully captured due to relatively low sample rate in this hand held DSO, the burn time and shape in that area is of interest. The burn time follows the spike an in this case lasts for 1.2ms.
The calibration of the Y axis is not stunning accuracy given the capacitive probe, sometimes comparison with other cylinders on a multi-cylinder engine or another similar engine provides useful information.
Let’s look at another instance of a similar GX200 clone.
Above is the ‘secondary’ voltage of the ignition system at 3400RPM and moderately low load (being a mulcher, spinning but otherwise unloaded).
The burn time is a little shorter at 1.1ms, probably a result of less fuel air mixture in the chamber.
So, there is nothing to indicate problems with ignition.
Mixture
The engine starts first go using starting fluid, and appears to run properly… so the problem seems to be that it normally needs a lot of pulls of the starter rope to get it to run.
First check was that the carburettor is secure, that there are not obvious sign of air leaks.
It was noted that when hot and adjusted to idle speed, speed increases a little with choking indicative of mixture being too lean, particularly from the pilot (idle) jet. The pilot jet was removed and a 0.35mm drill passed through it easily… I think I have already drilled this out to 0.4mm.
The main jet was inspected, it was #68 (equivalent to 0.027″) which is smaller than common (#70-#72). After a #81 substitution, the main jet was drill out from #68 to #77, and that greatly improved cold starting.
Altitude here is 700m, and although that is not very high, it is enough to make a difference to small engines and a small increase in fuel usually helps starting, performance and probably valve and valve guide life.