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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14923
Experience:  Certified on Onan and Generac generators
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I have a generac 7550 exl w/brigs and stratton motor. It starts

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I have a generac 7550 exl w/brigs and stratton motor.
It starts runs for about 30 seconds then shuts down.
There is plenty of (fresh) oil and it's not a fuel delivery problem (cleaned the float bowl)

Near the oil pressure sensor, there is a connected with 3 leads, when we disconnect that, it runs. (badly, very rough) but it runs.

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What is the model number of the genset?


This connector you unplugged, what color or number were the wires in it?


Customer: replied 5 years ago.
Model 01470

connector has 3 wires, White, Red, Yellow.

Also running like shit now (dunno if this is related to connector or messing w/carb) Seems to be running very rich now.

Was running fine all morning. Shutdown after showers this AM, started back up @ 6PM and had problems (did add fuel, which is fresh, bought just before the hurricane)

The 3-pin connector may or may not be the cause of the running - it is for ignition control and the oil alert monitor.

Plug it back in.


Go to the oil pressure switch, and remove both yellow wires from it. Isolate them so they can not touch ground.

Start the set.


Will it stay running now?

Is it running better?


Customer: replied 5 years ago.
I removed the 2 wires from the stud and taped them off.
I then connected the connector, it remained running (priviously this would cause the motor to shutdown after about 30 seconds)

Still running like shit, seems to be running really rich, quite a bit of smoke, hard to tell color (it's dark here)

The shut down is caused by either low oil pressure, or a bad pressure switch - most likely the switch.


The bad running is going to be a dirty carburetor.



This is a classic symptom of a carburetor that has become plugged with varnish.


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.

This condition is cumulative. Every time gas sits, the varnish builds up just a little more, like coats of paint, until eventually gas can not flow. It will not happen overnight, but the symptoms can show up all of a sudden, even while simply stopping to refill with gas.

The use of fuel additives, such as Sta-Bil or Sea Foam will not stop this process from happening. They will greatly slow it down, but the gas will still go bad.


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.

When removing the carb, make sure to take a good picture, or make a good drawing of where all springs and linkages are attached. This will make reassembly much easier.

Most people believe that cleaning a carb involves removing the bowl and wiping it out, then spraying some carb cleaner through it.

This is simply insufficient.

To properly 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, when one is available for your carb.


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.


If for some odd reason this does not help, please let me know so I can assist you further.


Customer: replied 5 years ago.
I'm thinking the float. We took it apart, as the initial indication was fuel starvation (the oil light never came on). It would run for the 30 or so secs, then stall.

We flushed it out with carb cleaner (I know not as good as a good soak in parts cleaner). It was running fine this morning, so we were thinking that I might have stirred some crap up in the tank when I fueled it.

I bet your right, the float isn't closing. (in 3 hours we used the entire tank of fuel, that normally last 8 hours)

I'll strip it down again in the morning when it's light out.


If it went through that much gas, also check you oil to make sure it is not contaminated with gas.


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