generator misfiring

Larry&Leisa

Larry&Leisa

Active Member
Oct 26, 2006
1,632
Keystone Lake Oklahoma
Boat Info
1999 330EC
Engines
454's
I think you would call it misfiring. When a load is coming off it ( such as the heater shutting off ) it makes a backfiring type noise. It seems like it over revs a bit then begins the 'pow pow pow'. I thought I would check the flame arrestor as I could see it sparking somewhat and when I took the cover off... no arrestor... Could this be cause of the misfire? ( bear with me.. I'm not very good at this mechanicing thing )
 
Need more information about the generator and symptoms. Manufacturer and model would help. Is it misfiring or backfiring? Does the engine surge when load is added or removed?
 
The generator maintains a constant RPM, probably 1,800 rpm, so the AC frequency is maintained at 60 Hz.

The symptoms sound like the mechanical governor is doing it's job to hold the RPM constant, but the carburetor is not regulating the air/fuel mixture as the load changes.

My guess is the throttle plate is sticking open, permitting more fuel than required, but it could be another carburetor problem.

Do an electrical test w/ a DVM to verify the generator side is maintaining the voltage at ~120VAC as the load changes. The problem might be related to loss of AC voltage regulation.
 
Kohler 5kw.. I guess backfiring.. as I said.. its as a load is coming off it that it does it. It starts great and had been running fine until recently. Fuel is fresh.. I checked the spark plugs and there was a bit of dry residue but otherwise seemed fine.
 
My Kohler 5kw goes through plugs like crazy. I've been told it's not unreasonable to expect to change them twice a year. Note though, that we don't use the generator very much and then not at full load.
 
That sounds like it's too rich, but to have that problem with a water cooled exhaust is weird. You're going to have to play with the throttle manually and see how the engine behaves. Since power is going to fluctuate, don't have any loads on the generator's output. Close the throttle and idle it down, then accelerate it up to speed and idle it back down again. Assuming plugs, cap, rotor, and ignition wires are good, popping on acceleration is a lean condition and one deceleration is rich. I guess it's rich since these things are setup rich for running under a load despite they mostly run under modest loads. Therefore with a little misadjustment and wear, it's easy to go too rich.

I'd do the ignition system first. It's more likely to cause a problem. After that, check the fuel system. There are other things that could cause a problem but very unlikely.

The carburetor's throttle plate has nothing to do with mixture. The choke plate does. Ensure that the choke is fully open and does not flop even partially closed at any time once the engine is warmed up. If the choke is OK, then you might need a carb rebuild. These things are simple so it's a simple and cheap job.
 
Thanks guys. Yeah Frank I did play with the throttle and could get it to do it upon deceleration. I thought if it was running rich tho that there would be oily residue on the spark plugs.. or perhaps it just hasn't had time enough for them to get that way. So what about the missing arrestor on performance?
 
No flame arrestor on the carb? Get one. They are required for safety reasons. Do you want open flames in your bilge when it backfires? Also when removed, it will affect generator performance.
 
Has this generator been used much? Typically the Kohlers need to be run regularly and under load. Try changing the plugs and running it under load. If you search on the forums others have addressed this problem as well this way.
 
What do the plugs look like?
Here are some examples.
MoparSparkPlug-Normal-Cold.jpg

MoparSparkPlug-Oil.jpg

MoparSparkPlug-Wet-Hot.jpg


Rich would also be "wet".

Best regards,
Frank
 
Had this same issue. I called it "popping" when I called a genset repair. He was familiar with this and the plugs were replaced and it runs like a charm, load or not.
 
STOP. even though the plugs look good

REPLACE THEM Koeler gennys go through plugs like crazy,
replace them with the "Auto-Lite" brade equivalent
 
Finally got around to installing new plugs and sure enough that took care of the issue. (I also have the flame arrestor ordered...hopefully get that installed next weekend)
 
Glad to hear it.
 
Larry&Leisa said:
Finally got around to installing new plugs and sure enough that took care of the issue. (I also have the flame arrestor ordered...hopefully get that installed next weekend)
Click to expand...

Glad to hear it. Keep three sets of plugs on board. One in the gennie, and 2 spare sets. I have no idea as to why Kolhers eat plugs, but 9 out of 10 problems with that brand seems to be able to be solved with plugs.
 
Just thought I'd give an update. Got the arrestor and air intake/filter parts in and installed this weekend. Have to say it definately sounds better and seems to run even better now. Thanks to all for the help. ( and yes I have an extra set of plugs on board as well )
 
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