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My Onan Microlite 2.8 kW generator keeps stalling when the…

My Onan Microlite 2.8 kW...
My Onan Microlite 2.8 kW generator keeps stalling when the AC attempt to start.

This was not a problem until recently.

Before the generator started stalling on AC start, it would stall when taking sharp corners if the genset was running while we were moving.

I have recently changed the oil, air filter, and spark plug.

The basic question is how likely will cleaning the spark arestor or changing the fuel filter solve the problem?

I tried to clean the spark arrestor, but I'm currently stimed by a stuck exhaust pipe.

I am up for changing the fuel filter, but it will take a couple of days to get the part.

I don't want to mess with either if I'm still going to have to take it in for service anyhow.
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Answered in 48 minutes by:
6/27/2010
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15,993
Experience: Certified on Onan and Generac generators
Verified

The stalling while putting a load on it is indicative of 2 things:

1. The set not getting enough fuel.

2. The engine running too slow.

 

When the set is running with no load on it, is it surging (constantly speeding up and slowing down)?

 

Does the engine sound like it is running at normal speed, or does it seem to be running slower than normal?

 

Do you have a multimeter that is capable of measuring frequency?

 

Changing the fuel filter will most likely not solve the problem, especially since you stated that before the set would quit when turning sharp corners. This is indicative of a different issue - a partially restricted carburetor.

 

To test for this, remove the air filter.

Turn the breaker off at the genset.

Turn on the A/C.

Start the set.

As you turn on the breaker at the set, start spraying some gas or carb cleaner into the intake.

Will this allow the engine to pull the load - even if it runs a bit rough?

 

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Customer reply replied 8 years ago

When the set is running with no load on it, is it surging (constantly speeding up and slowing down)?

 

No.

 

Does the engine sound like it is running at normal speed, or does it seem to be running slower than normal?

 

Maybe - it seemed to be running more smoothly after the oil change at any rate.

 

 

 

Do you have a multimeter that is capable of measuring frequency?

 

I do.

 

To test for this,

...

Will this allow the engine to pull the load - even if it runs a bit rough?

 

If this does work, what does that imply I need to do next?

If adding the extra fuel allows the engine to pull the load, it means that the engine is not getting enough fuel - most often due to a partially restricted carburetor.

This is a very common malady for gensets.

The solution would be to clean or replace the carb.

 

 

As gas gets old, it turns to varnish and clogs up the passageways inside the carburetor, not allowing enough gas to get to the engine.

When this happens, either the engine simply will not start, or it will not run without the choke on (this reduces the amount of air getting pulled into the engine, changing the fuel/air mixture), or it will run but surges.

 

Another issue that varnish in the carb can cause is that the varnish may not allow the float needle to seal properly against the seat, causing the flow of gas to not shut off when the bowl is full. The result will be gas overflowing the carb and running into the cylinder, and possibly out the air intake. If the gas gets into the cylinder, it will seep past the rings and down into the crankcase. This will be evidenced by your oil level being over-full and/or the oil smelling like gas.

 

The only 2 solutions are to either replace the carburetor or give it a good, thorough cleaning.

To clean the carb, you must remove it, disassemble it (making sure to remove all non-metal parts), and soak it in a commercial solvent for several hours. Soaking it overnight is even better.

Then clean all solvent off with a spray type carb cleaner, making sure to get lots of cleaner into every hole and passage there is. Pay special attention to the tiny holes in the bore of the carb, under the throttle plate for the carbs that have these holes. Use lots of cleaner. And make sure to wear safety goggles to avoid getting the over spray into your eyes. There will be over spray.

Dry the carb with low pressure compressed air.

When reassembling the carb, make sure to use a carb kit.

 

Occasionally, even a good cleaning is not going to be sufficient, and you may end up having to replace the carb anyhow. Be prepared for this.

 

 

 

The first thing I would like you to do is to measure the output frequency of the set. It should run at about 62.5 Hz with no load applied.

If the engine is running too slow, it can create all kinds of problems.

 

If the frequency is good, do the spray test and let me know what happens.

 

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Customer reply replied 8 years ago

Of course, the generator is now dying about 30 seconds after starting, even with no load applied, so I'm not able to get a freq measurment.

 

It would be tommorrow at the earliest before I can do the spray test.

 

However, I'm ready to just replace the carb if it sounds like that's most likely the issue.

 

If it is advisable to replace the carb, the procedure I have for this is:

- Disconnect the gas line.

- undo the intake manifold bolts on the engine side,

- slide the carburetor and the manifold out half way,

- undo the two hex head screws that hold the carburetor to the manifold,

- side out the carburetor and undo the linkage.

 

Looking at the parts diagram it looks like I could skip undoing the manifold bolts. Is this advisable/possible?

 

Thanks!

The carb is still the most likely suspect, but it is not very cheap.

I definitely would not recommend replacing it until we have checked the frequency and done the spray test.

If the set is running too slow to begin with, it will not pull a load.

It may simply need a governor adjustment.

 

On removing the carb - sometimes you can get away with not pulling the intake manifold. But I have seen a couple of sets where the 2 screws that hold the carb on are offset from the opening, and you could not get to them without pulling the manifold.

You can use an inspection mirror to look in there and see.

 

Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15,993
Experience: Certified on Onan and Generac generators
Verified
Hank F. and 87 other Small Engine Specialists are ready to help you
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You can check the output by removing the control panel and testing at the back of the circuit breaker. The set will not have to run for more than about 5 seconds that way.

 

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