Hello,
 
I'm repairing a Zipper ZI-STE3000IV inverter generator. It's a Chinese design with GX clone engine inside.
I did a lot of work on the generators itself in the past (diagnosis, custom build AVR etc.) but not so much on the engines itself beside carb cleanup, spark plug and spark plug cable/connector replacements.
 
It has troubles starting especially when sitting for a few days. The owner said that he was not able to start it but I managed to do so before I did anything to it (without using any chemical help.). With out load (smart throttle on) it was running a little bit rough, but no issues under 2 kW load. I removed the carb and tear it apart including idle and main jet and then put it into the ultrasonic bath. Everything seems pretty clean to begin with. I also replaced the spark plug. When doing the disassembly I noticed that there's a lot of oil in the air filter housing at least from my previous experience. There was also some oil on the bottom of the valves cover (I didn't bother checking the seal.). Oil levels are fine.

After cleaning everything I put it back together and try to start it every other day or so and it was kind of ok. Today after sitting for a few days I wasn't able to get it running. I eventually succeeded by putting some gasoline directly into the cylinder and after that it was working fine. I let it idle for a minute and then do a few restarts, all without an issue.
 
Fuel is reaching the carb for sure. Spark is there if it runs fine. When I was having issues starting it I checked the spark and it was dry. The only thing that I can think of is the compression issue that would explain the extensive oil in the air filter box coming from the head breather tube and inability to suck the mixture from the carburetor. Or maybe I'm just doing something wrong.
 
As far as I know from online resources and experience with similar engine tear down it has an automatic decompression which makes a regular compression test useless.
 
For a pressure test the piston must be put in a top dead center and even if I succeed doing so with a cord there is no way that I can prevent the engine from turning over without disassembling the whole generator in order to get to the crankshaft.
 
Any ideas or suggestions?
 
Best regards,
 
Primož
 

I agree, it sounds like the compression rings are leaking, causing blow by and pushing air into the air box.  That should be dry.
 
Pull the valve cover off, watch the valves at TDC, compression stroke, til their both closed.
(That or just loosen the rockers so the valves are fully closed)
 
Now you can do a leak down test.  I will usually put a socket / breaker bar on the flywheel crankshaft nut, set it up so the bar locks up on the frame(of course being very, very careful it doesn't come off).
 
Slowly add air, (making sure the breaker bar is safe). I go to 100PSI and listen for leaks and of course see what the gauge shows..
 
I do also agree that it's very possible the engines not sucking fuel in thru the carb due to the rings.
 
 
 
 

Thank you for your answer. I bought a tester and finally did a test today. As it seems it leeks quite a bit so I guess that's not normal. The engine was cold and I didn't add any oil into the cylinder. Test was done at 7 bar, so roughly 100 psi.

As far as my knowledge go, those can be rings or the head gasket. Maybe I can put some oil in the cylinder and if the change is not dramatic the head gasket is blown.

You can find images and a video of a test on the link bellow. I improvized with the engine lock, but it worked. I just made sure that the engine was at a start of combustion stroke in order not to turn in the undesirable way.

https://1drv.ms/f/s!AtqR3TY1Zt51n0d86fk52JFngbL2

Thank you very much for help in advance.

I don't know how much I trust your leak down tester...  
 
Your gauges should closer to this (this engine failed):

 
Even if you pump air direct into the combustion chamber (TDC / combustion stroke), you should be able to hear air coming out the (if bad), the carb(intake valve), exhaust(exhaust valve), or oil fill opening(bad rings)...
 
What's the compression of the engine?
 
.

I did a research how those leakage tester actually works. You have a pressure regulator, then main pressure gauge, then small passage and then leak indicator. The leak indicator is a preassure gauge on mine and on yours but mine has a scale in percentage. Because of the small air passage there is a pressure drop present which value corresponds to the amount of a leak.

At first you connect it only to an air supply with the output hose disconnected/closed. You set the pressure regulator on the tester so that the leak gauge shows zero. Then you can proceede with a test. In my case the leak tester is designed for low pressure tests so that's way I can not achieve 100 psi.

Did you check the video on the link (one drive) which I posted in a previous post? You can hear the air escaping into the crankshaft housing. It seems like a lot of air, but I do not have enough experience to judge.

From my knowledge the inbuilt automatic decompression does not allow for a regular compression measurement.

I'm not sure I understand how your gauge works.
 
You are correct on mine. It's plumbed into the combustion chamber, (TDC Compression stroke-((2 stroke shown)).  The air is added (crank locked up like yours).  15% is about the max leakage amount.  
 
Sooo, at 100PSI, you should have at least 85PSI showing.   Using low pressure could show leakage but not accurately.
 
Loosen both valve rockers at TDC (by-passing the compression release).  I suspect your results will be the same, air coming up thru the crankcase.  
 
I suspect your probably going to have to remove the head to check for a possible blown head gasket. 
If no failure is present, worn rings are very likely your issue.  
 
Also, using a compression tester, you can still get pretty accurate results even with a compression release.   
 
Now, once you get a base line #, add some oil to the cylinder(couple of teaspoons).  Try the test again.  If the compression rises, your rings are most likely the issue.  The oil helps make a seal temporarily..
 
For stubborn 2 strokes especially, that haven't been in a long time, that added oil will very often help the engine to start (warm up and rings to seal)..

Primoz
Hello,
 
I'm repairing a Zipper ZI-STE3000IV inverter generator. It's a Chinese design with GX clone engine inside.
I did a lot of work on the generators itself in the past (diagnosis, custom build AVR etc.) but not so much on the engines itself beside carb cleanup, spark plug and spark plug cable/connector replacements.
 
It has troubles starting especially when sitting for a few days. The owner said that he was not able to start it but I managed to do so before I did anything to it (without using any chemical help.). With out load (smart throttle on) it was running a little bit rough, but no issues under 2 kW load. I removed the carb and tear it apart including idle and main jet and then put it into the ultrasonic bath. Everything seems pretty clean to begin with. I also replaced the spark plug. When doing the disassembly I noticed that there's a lot of oil in the air filter housing at least from my previous experience. There was also some oil on the bottom of the valves cover (I didn't bother checking the seal.). Oil levels are fine.

After cleaning everything I put it back together and try to start it every other day or so and it was kind of ok. Today after sitting for a few days I wasn't able to get it running. I eventually succeeded by putting some gasoline directly into the cylinder and after that it was working fine. I let it idle for a minute and then do a few restarts, all without an issue.
 
Fuel is reaching the carb for sure. Spark is there if it runs fine. When I was having issues starting it I checked the spark and it was dry. The only thing that I can think of is the compression issue that would explain the extensive oil in the air filter box coming from the head breather tube and inability to suck the mixture from the carburetor. Or maybe I'm just doing something wrong.
 
As far as I know from online resources and experience with similar engine tear down it has an automatic decompression which makes a regular compression test useless.
 
For a pressure test the piston must be put in a top dead center and even if I succeed doing so with a cord there is no way that I can prevent the engine from turning over without disassembling the whole generator in order to get to the crankshaft.
 
Any ideas or suggestions?
 
Best regards,
 
Primož
 

it seems like there may be a compression issue with the engine, which could explain the difficulties in starting the generator, especially after it has been sitting for a few days. Here are a few suggestions you can try:

1. Check the Valve Clearance: Improper valve clearance can affect compression. Consult the engine's manual to determine the correct valve clearance specifications for your specific model. Adjust the valve clearance if necessary.
   
2. Inspect the Head Gasket: A damaged or worn-out head gasket can cause compression loss. Remove the cylinder head and inspect the gasket for any signs of damage or wear. Replace it if needed.
   
3. Check Piston Rings: Worn or damaged piston rings can also lead to compression issues. This requires removing the piston, which may be more involved. Inspect the rings for any signs of wear, and if necessary, replace them.
   
4. Address the Oil Issue: The presence of oil in the air filter housing and valve cover suggests potential problems with the engine's lubrication system. Ensure that the oil level is correct and that the breather tube is not obstructed. It's also worth checking the PCV (Positive Crankcase Ventilation) valve, if applicable, and clean or replace it if necessary.
   
5. Fuel System: Although you mentioned that fuel is reaching the carburetor, it's worth double-checking the fuel delivery system. Ensure that the fuel filter is clean, the fuel lines are clear, and the carburetor is properly adjusted.
   
6. Consider a Leak Down Test: A leak down test can help identify any internal leaks or issues with valves or piston rings. This test requires specialized equipment and knowledge, so if you're not familiar with it, you might want to consult a professional or a specialized repair shop.
   

If none of these steps resolve the issue, it may be helpful to seek the advice of a professional mechanic who specializes in small or contact the manufacturer for further assistance.  

Primoz
Thank you for your answer. I bought a tester and finally did a test today. As it seems it leeks quite a bit so I guess that's not normal. The engine was cold and I didn't add any oil into the cylinder. Test was done at 7 bar, so roughly 100 psi.

As far as my knowledge go, those can be rings or the head gasket. Maybe I can put some oil in the cylinder and if the change is not dramatic the head gasket is blown.

You can find images and a video of a test on the link bellow. I improvized with the engine lock, but it worked. I just made sure that the engine was at a start of combustion stroke in order not to turn in the undesirable way.



Thank you very much for help in advance.

Yes man