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Old 12-04-2012, 09:07 PM   #1
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Kohler - 7cm21-rv generator problems

I've finally gotten around to working on the Kohler generator in our 310. It has always been difficult to start (crank and crank and crank and finally start) until recently when once you got it started it would run ok until you turned it off at which point a fuse would blow inside the control box.

It took me about 6 fuses to finally isolate the problem to the shutdown solenoid. What was so odd about the situation is the fuse would not blow during start up which is when power is first applied to the shutdown solenoid (solenoid stays energized any time ignition coil has power). It would only blow when pushing the stop switch. You would see a nice little arc inside the fuse when it blew.

I believe the solenoid has been gradually failing because the generator had been getting harder and harder to start. It has a resistance reading between 0.000 and 0.002 ohms. What I found interesting is with the shutdown solenoid removed from the circuit not only does the fuse stop blowing but the generator actually starts almost immediately upon pushing the start switch.

While I was in the process of removing the solenoid I noticed that the plunger seemed to stick or bind in a couple of spots. I don't know if this had any affect on the overall operation but it certainly didn't help any.

I tested the solenoid on the bench this evening by connecting two wires to the spade connectors and then connecting one lead to the positive terminal of the battery. I would then touch the other wire to the negative terminal. There was no spark on application of power but as soon as I removed the wire a large spark occurred. After a few tests like this I noticed that the wire was starting to get real warm (16 gauge). The solenoid shows signs of the potting having melted so I'm guessing the solenoid is shorted inside and causing a higher than normal current draw. Why it arcs so bad when removing power baffles me. I would have expected the same sort of spark to occur when I applied power but it's not. Also when the solenoid was on the genset the generator would stay running even though the solenoid was obviously drawing a lot of current. The 10 amp fuse would not blow until power was removed.

Oh yeah, I did the typical guy thing and tried using larger fuses to see what would happen, they blew of course

The only other issue now is the way the generator is actually running. This is a new problem I haven't sorted out yet but I think it is choke related.

Here are links to two videos, the first one is just after start up. You can hear it surging and then after a while (a minute or three) the surging seems to settle down but it still seems to be running a little rough like it has a miss. What is odd is right after it fires off it runs real smooth and after 6 to 10 seconds is when it starts the surging. I'm guessing the electric choke isn't functioning correctly mainly because it seems to put out a blackish exhaust during the time it surging. The second video is with the generator running under a load and having warmed up for a few minutes. The first video was taken with the two circuit breakers turned off so there was definitely no load on the generator.

Kohler Just After Startup

Kohler Warmed Up With Load

Any suggestions on what I should be looking for to keep it from surging?

Thanks!

Brad
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Old 12-05-2012, 09:16 AM   #2
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The reason for the arc during de-energization of the solenoid is because the, when the electric field collapse in the coil (when power is removed) then the coil induces a reverse current. This is normal. The real problem may not be isolated to the solenoid alone although it may also be defective. Normally there's a reverse diode across the solenoid that shunts the reverse current. I don't know if the diode is in the solenoid or external on your unit but it seems that the diode may be bad as well. Check the Kohler schematics to see if yours is supposed to have the reverse kick back diode. I'd be surprised if it didn't.
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Old 12-05-2012, 12:46 PM   #3
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92landyacht, that makes sense as to why an arc would be generated.

I did a little more research last night and also bench tested the solenoid. Turns out the schematic I had doesn't quite match my generator. I found the operators manual that actually came with the generator (the service manual was one I found on line) and it had a schematic that differred in how the solenoid was connected.

The solenoid is actually called an Air-Shutoff solenoid, not Shutdown solenoid. This solenoid is energized when you depress the Stop button. It is wired on the same side of the fuse as the ignition coil but has a relay contact between the fuse and the solenoid keeping the solenoid de-energized until the Stop button is depressed.

When I bench tested the solenoid it would function but after holding the wires for about 3 to 4 seconds they got to hot to hold because of the high current draw. The solenoid is definitely shorted inside which accounts for the fuse blowing.

The good news is the generator can operate without the solenoid, it just might diesel on shutdown. So far it hasn't done that but if it does I'll deal with it at that time.

Now to figure out the surging problem and I'll be set.

Thanks!

Brad
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Old 12-06-2012, 11:34 AM   #4
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Good thread and good info!
I will be needing some help too when I get back to mine!
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Old 12-06-2012, 11:43 AM   #5
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Good thread and good info!
I will be needing some help too when I get back to mine!
Depending on which version of Kohler 7CM21 you have there are two different "shut-down/shut-off" solenoids. My version had the air shut-off solenoid which is only energized when the off button is pushed. The other version (newer) uses a fuel shutdown solenoid that uses a plunger to block the fuel path. The earlier version which is what I have only energizes the solenoid when stopping the generator. The newer version energizes the shutdown solenoid any time the coil is energized which keeps the plunger out of the fuel flow path.

The problem you've described on your generator almost sounds like you have the newer fuel shutdown solenoid and it might be drawing two much current. Regardless you definitely shouldn't have less than 12vdc at the positive coil connection.

Brad
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Old 12-06-2012, 11:51 AM   #6
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Hi bkahler: Surging can be caused by two problems. 1] insufficient fuel supply which includes poor fuel quality. 2] streched or weak govenor spring icluding misadjusted bellcrank on govenor's shaft. Thanks, "Boatdoc"
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Old 12-06-2012, 12:08 PM   #7
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You know what Brad...
If mine is the later type, that could explain why I get no suction from the pump when mounted, but it works fine on the bench!

If the fuel path is blocked, its possible that would explain the slight push back or positive pressure instead of suction I mentioned that prompted you to correctly suggest a reversed wire on the pump feed!

I also noticed a loose wire coming from the back side of the carb yesterday!
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Old 12-06-2012, 12:22 PM   #8
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Assuming yours is the later style the good news is you can remove the plunger which will allow the generator to run. Either the Operator or else the Service manual states that you can remove the plunger. All it really does is keep the generator from dieseling on shutdown.

Hopefully you've solved your problem

Brad
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Old 12-06-2012, 12:45 PM   #9
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Hi bkahler: Surging can be caused by two problems. 1] insufficient fuel supply which includes poor fuel quality. 2] streched or weak govenor spring icluding misadjusted bellcrank on govenor's shaft. Thanks, "Boatdoc"
Boatdoc,

Would or could the governor spring cause a slight miss while running? That's the one thing that I hadn't noticed before while running the generator. The surging after start up occurred just recently. It used to surge at times when running under load but I think that might have been partially caused by the sticking shut-off solenoid.

I'm sure it is probably due for new plugs so I'll try and replace those this weekend to see if that helps.

Thanks!

Brad
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Old 12-06-2012, 01:47 PM   #10
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You know what Brad...
If mine is the later type, that could explain why I get no suction from the pump when mounted, but it works fine on the bench!

If the fuel path is blocked, its possible that would explain the slight push back or positive pressure instead of suction I mentioned that prompted you to correctly suggest a reversed wire on the pump feed!

I also noticed a loose wire coming from the back side of the carb yesterday!
I was just looking over this thread kohler 7000 oil leak and noticed that your 7CM21 is not like mine. If you don't have a large (1.25" x 2.5") solenoid hanging under your coil that is held in place with a hose clamp and has a chain that connects the plunger to the governor lever then your's is likely the newer model with the the fuel shutdown solenoid instead of the air shut-off solenoid.

The main reason I was looking at the oil leak thread again is because I'm getting ready to perform the piping mod that you pioneered. We'll see if it goes as easy for me as it did for you

Brad
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Old 12-06-2012, 02:33 PM   #11
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Yes, I replied to your questions over there!

Ok... as someone may have noticed... I take lots of pictures....
Here is a shot of the Coil area... no solenoid below it..
But looking at the picture, I wonder if that is an oil pressure switch in the top of the crankcase below the coil... hope not... cos it not connected...

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Old 12-06-2012, 03:39 PM   #12
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Yes, I replied to your questions over there!

Ok... as someone may have noticed... I take lots of pictures....
Here is a shot of the Coil area... no solenoid below it..
But looking at the picture, I wonder if that is an oil pressure switch in the top of the crankcase below the coil... hope not... cos it not connected...

Not sure what that is. I'll look tonight at mine.

Looking at the same picture if you'll notice that small bracket hanging down from below the left end of the ignition coil. The air shut-off solenoid on mine hangs from that bracket.

Brad
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Old 12-07-2012, 03:38 PM   #13
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Hi bkahler: Weak spring will cause out of balance condition between load factor and engine output causing flux in fuel supply. But as a rule of thumb there is a problem with fuel supply. Hope this helps. "Boatdoc"
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Old 12-07-2012, 03:53 PM   #14
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There are multiple positions on the spring arm, and all of them are for different applications...
Make sure your is in the right holes!

Going over to the storage today, so will take a better look at my gen this time take some pics.
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