OT: Need help with Generac 5500XL overspeeding

So, the Generac 5500XL (09778-3) whose carb I mentioned in the bad gas thread is back together with its shiny clean carb. Set the choke and it started on the third pull like new. Turned off the choke and the motor went to a pretty high RPM but ran fine. Checked the output voltage and measured 145/290, 12.6 on the DC output. Crap. By manually moving the throttle lever I can get the RPMs down and the voltage to around 124, DC output at 10.6.

The manual says to adjust the idle but not let the frequency go below 45 hz. Well, I don't have a way to measure that.

Checked on the Internet and YouTube but haven't found anything that helps.

I always take photos of anything I'm about to take apart so am pretty sure it is back together correctly. One bit of concern is a spring on the throttle rod and just connects to the holes that hold each end of the throttle rod. Seems odd that a manufacturer would put on a spring that seems to serve no purpose. Pictures show it that way before disassembly but maybe I worked on it two or three years ago and moved the spring. It seems like I would fix the problem if connected differently but the only place it could be connected to otherwise, it isn't long enough to reach.

Anyone know anything about portable generators and what I might be able to check? What I'm calling the throttle rod is the rod on the upper left.



Thanks.
Steve

That little spring's purpose may be to keep the freeplay out. I think I have a genset like that ,but cant get to it now. If you can measure the rpm, set the rpm to 3600+ under a medium load. Are you are speaking about no load speed?

I have a Kill-A-Watt which I bought a few years back to measure electrical usages. Turns out it also can measure AC Hertz!!

So I fired it up and when speed is near idle, voltage goes to about 122v with 60hz. Good to go on that. Looks right now like the problem is that when the load is applied, the throttle is supposed to be opened more to keep the RPM/Voltage/Hz in the proper range. I can manually open the throttle under load and get it back to 122/60. So now I know what the solenoid right in the middle of the picture is supposed to do. I'll test the solenoid tomorrow but I think that is the problem.

Steve

Sounds like you don't have the governor working correctly. It should maintain engine speed under load so that the frequency is pretty close to 60 Hz.

That threaded rod with the spring attached in the foreground is the governor. Changing the tension changes the RPM at WOT. Usually these things never idle to no real need to get idle correct.

To set correctly you need a meter that can read frequencies, and set if for around 62 Hz. Many digital ones will do that. You might be able to get in the ballpark by just setting the voltage, but I would not trust it for any sensitive electronic devices.

Usually the governor on a small generator has "something" (a lever of some sort) sticking out of the block that connects to a spring that connects to the throttle plate on the carburetor. At rest, the throttle should be wide open (held by light spring pressure) and as rpm increases, the throttle should gradually close to limit the rpm to 3600 (or 1800 depending on design).

In my experience, when the rpms are way too high, it's frequently because the governor lever is stuck due to corrosion or similar. Remembering that the throttle is fully open when the motor isn't running (i.e. when stored for long periods) means the governor seizes up wide open so your rpm overspeeds once you get the motor running again.

Check to make sure all the parts which are supposed to move really do move. On my General 8000XP the governor sticks open more often than the carburetor clogs up!

gnorbury said:

In my experience, when the rpms are way too high, it's frequently because the governor lever is stuck due to corrosion or similar.

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Yes, and judging from the grunge in the pic, corrosion looks to be a likely cause.

The governor on little engines is often a plastic vane in the cooling air stream,and subject to dust ,dirt,grass etc .

john.k said:

The governor on little engines is often a plastic vane in the cooling air stream,and subject to dust ,dirt,grass etc .

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Not usually on these Honda clone engines. Usually it's in the crankcase.

Just a little followup. The "grunge" is just a light coating of dirt that is easily wiped off. There is no corrosion and all the parts move freely. As I indicated the governor is not mechanical, it's electrical. I'm hoping to get a chance to work on it this week but frankly diagnosing electrical issues is a weak area for me.

Steve

As a blacksmiths guide to electronic repair......usual is to first look for bulged capacitors and burnt resistors....beyond that....

SteveF said:

Just a little followup. The "grunge" is just a light coating of dirt that is easily wiped off. There is no corrosion and all the parts move freely. As I indicated the governor is not mechanical, it's electrical. I'm hoping to get a chance to work on it this week but frankly diagnosing electrical issues is a weak area for me.

Steve

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Are you sure about that? The item you posted a photo of looks more like an idle control solenoid. It also sure looks like governor linkage coming out of that metal shield. I'd be more than a little surprised if that engine has an electronic governor. Post some better photos.

I just did a quick Google and found your generator's schematic. There's no sign of any electronic governor, but there is mention of an idle control coil. I'd assume that it sets the engine back to idle at no load.




Briggs & Stratton Power 9778-3 - Generac XL Portable Generator, 5,500 Watt Electrical Data Drawing No. 92670 Diagram and Parts List | PartsTree.com

The rod coming out of the shield hole in the upper left is directly connected to the throttle plate in the carburetor under the shield. If there is a mechanical governor it must be inside the housing between the gas engine and the electric motor. Thanks for looking up the solenoid, now I know its correct name and sounds like it doesn't do what I thought it did.

The generator worked fine until a couple of years ago when I could get it to start with difficulty but when a load was applied the engine stopped. A buddy thought it might be a constricted jet wasn't allowing enough gas to support a higher throttle opening but now that the carb is completely clean, it must be governor related.

Learning something new every damned day!!

Steve

Finally got a chance to finish fixing this generator so making this post to finish up the thread.

The problem was that when I took off the governor assembly and such to get off the engine cover, I didn't realize the control arm has to go back on the shaft in EXACTLY the same position as where it was. If I have to do it again, I'll put a punch mark on the intersection of control arm and control shaft to make this easier.

If you haven't come across this guy, his videos are great. Skip past the first three minutes if you don't like the amateur comedy. The info is very well presented.

YouTube

So with the governor correctly adjusted, it runs fine.

BTW for anyone involved in designing generators:

(ahem)

ATTENTION MORONS.

Due to this wonderful ethanol in the gasoline, at some point the carburetor may need to be removed in order to clean it. There is a control rod connecting the governor to the throttle plate. This rod has to be removed from the carb in order to get the carb off of the engine. If you design it so that in order to get the rod out of the throttle plate, you have to remove the entire engine cover, and to remove the cover you have to remove all the external pieces of the governor, I hope you die soon.

Also, at some point fuel will need to be drained so fresh fuel can be put in. At least make the fuel lines accessible so a drain line can added or it is easy to pull one end of the line loose.

Steve