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Engine Power Loss


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04-19-04, 05:56 AM   #1  
south
Engine Power Loss

I have a kohler Magnum 12 on a ferris walk behind mower. The problem I am having is as follows: The engine starts and runs strong for 10-15 minutes, then wants to quit. If I half choke it, it will run, but not at full power. Once I let it sit for a little while (20-30 minutes) it will repeat the process.

Any suggestions would be appreciated.

Info: the engine and mower have been sitting all winter in a barn and wouldnt start, I had my local shop tune the engine and got it running this spring.

 
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04-19-04, 10:07 AM   #2  
Breathe baby breathe.

Sounds as though you have a problem with the fuel tank not breathing properly. When gas is removed from the tank (by means of running), that gas must be replaced by air. I believe the fuel cap is vented on your machine, enabling it to breathe. Be sure this vent hole is free. If you are uncertain whether the fuel cap is at fault, slightly "crack" the cap loose and run to check. I would be sure the fuel level is low enough so that it does not slosh out while trying this out.

 
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04-21-04, 09:00 AM   #3  
south
Thanks,

I checked the vent on the gas cap and it seems to be venting OK. I took it off and blew through it, didn't seem to have any obstructions.

I pulled the air filter off last night and gave the carb a shot of carb cleaner. The engine fired up and ran good. I will be mowing this evening, will reply if the same thing happens again.

 
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04-21-04, 03:55 PM   #4  
Magnum 12???

I've never seen a horizontal shaft engine on a Ferris walk-behind unit. Are you sure this is a Magnum 12? Nonetheless, your trouble may be difficult to assess without actually having the machine on-site, but here it goes. If you are absolutely certain the FUEL TANK is breathing and based on the time it runs well for, two issues come to mind. First is the ignition. It may be breaking down once the engine gets up to operating temperature. Second would be valve-train related. Again, once heated up, (and when cold you have little to no intake valve clearance) you may be experiencing power loss due to a lack of vacuum on the intake. Checking ignition: You will need a simple ignition tester, which is placed in-line between the plug terminal and the spark plug. Kohler, Briggs and Tecumseh all have these testers available. With the tester hooked up, run the engine at top RPM, all the while you will be watching the tester for either intermittent spark of spark failure alltogether at the moment the engine begins to sputter. Checking valve clearances: Either go right ahead and remove the valve cover and physically check with guages or, if tool is available, perform a leak-down test of the combustion chamber. A leak-down test should be performed when the engine is at operating temperature, while the valve clearances will be checked when the engine is cold.
Check back here for a reply from cheese as well. He may have another idea as to what trouble you may be having. I'm sure he will post in by tomorrow, at the very latest. Let us know.

 
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04-23-04, 01:07 AM   #5  
Hello South!

I agree that the first thing that comes to mind is a tank vent problem. Did you try loosening the cap to see if it stopped the problem? If that doesn't do it, remove the fuel lines and check to see if they are old and deteriorating on the inside. The lining can swell and partially restrict fuel flow. If it restricts it bad enough, it will eventually cause the engine to lean out (which it seems to be doing since you can keep it running by pulling the choke). Check the fuel filter too. Make sure fuel flows freely out the end of the line at the carb.

The next thing I would suspect would be valve clearance issues.

An ignition problem is possible, but the thing that makes me want to check fuel related things first is the fact that you can keep it running by pulling the choke. Once in a while, an ignition problem will exhibit itself in a strange way, and that could be the case here, but I would check the fuel system first.

Another thing to check...make sure the bowl vent on the carburetor is not clogged.


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04-23-04, 04:39 AM   #6  
south
Thanks for all the advice and suggestions. I will let you know what I find out.

 
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04-26-04, 08:48 AM   #7  
south
Finally dried up enough to mow this Saturday. After about 45 minutes of mowing, the engine started running rough, and would remain running while choked. I let it sit for maybe 10 minutes and it fired up and I continued to mow. Another 45-50 minutes later, same thing. This time I had the cover off the air filter and I kept it running long enough to get the air filter off. I was working the choke back and forth and I noticed that there wasn't any gas around the choke (I noticed because it just seemed unusually dry at and immediately inside the choke.) Then all of a sudden it started running again and I finished mowing.

I tried taking the gas cap off, did not help. I do think it is definitely a fuel flow problem. Could it be the float in the carb bowl is sticking shut? Is there anything I can do short of pulling the carb to clean it?

Thanks
South

 
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04-26-04, 09:24 AM   #8  
This sounds like a ignition symptopm to me. Sometimes when ignition coils break down they have mysterious symtoms, such as, aftor the engine heats up, your ignition coil starts acting up. I had that problem with a weedeater of mine that had the same symptoms. It would run for 20 minutes and then it would quit. But if I let it sit for a while, it woul be back up and runing. It could be that your sparkplug wire is cracked and the wires exposed, or your kill wire could be exposed, or the coil itself could be your culprit. Lets see what the others think.

 
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04-26-04, 03:33 PM   #9  
Choker

In the time the engine does run well, do you need to use any choke at all? When it does begin to break down, how much choke is required to keep it running smooth? Your run time to breaking down has changed since your first post, do you have a different fuel tank level now than the first time...possibly considerably less fuel? Do you have access to the ignition tester which I mentioned in my second reply? As far as cleaning the carburetor without pulling it off, spray cleaners tend to work fairly well so long as you don't have considerable varnish build-up. You should still at least remove the bowl as well as any adjusting needles and spray into these cavities using a good quality spray cleaner, I recommend Briggs Carburetor Cleaner...it works very well and evaporates quickly. Let us know the answers to these questions.

 
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04-27-04, 12:47 AM   #10  
I still think you have a fuel related problem, especially now. Did you check for a good volume of fuel flowing from the fuel line at the carb end when removed?


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04-27-04, 08:23 AM   #11  
south
I was wrong on the run time in the intial post. It should have been closer to 40-45 minutes.

When running well it requires no choke.
No access to ignition tester.

Feul flow seems good, although I dont know what good fuel flow would look like. I am replacing all the fuel lines and the filter, before I tear into the carb.

 
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04-27-04, 09:42 AM   #12  
Engine #'s

How about engine numbers so that, if needed, we can help you with carburetor service.

 
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04-27-04, 04:14 PM   #13  
Engine Power Loss

Hi South,sounds like you have a problem.I have reviewed all the posts.Let me throw something out there.OK,ignition trouble & fuel problems can sound the same,and can be most difficult to zero in on.
On a coil especially an electronic ignition coil,the only warning that they give when it's going bad is when it does go bad.There either work good or they dont.Ane most of the time the engine stops just like someone turned off a key.And a ground wire colud do this, or arc till engine quets,sounding just like spitting and sputtering, witch leads one to to beleive it's either starving for fuel or maybe flooding.

You didn't see anything wrong with fuel cap or fuel lines.I always put fuel cap to my mouth and breath through it (if I can ,the tank can).
One time tho I was working on a 8Hp.B & S blower,tryed all the stuff that your talking bout,didn't work.I was at point of pulling my hair out when I found it.The fuel tank had a piece of cardboard in it.After about 15-20 minutes it sucked cardboard over fuel outlet hole in bottom of tank.Then after it quet it would float back to top.Run me crazzzzzzzzzzzzzzzy

 
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04-28-04, 03:36 PM   #14  
Weak ignition

With due respect to repair_guy, I, just today, had a coil with insufficient spark...not no-spark. I have seen countless instances of weak ignition, related solely to the armature, in my years in this industry. I can't tell you how many technicians and customers that have subscribed to the theory of a coil being perfect or dead, with nothing in between. I'm here to tell you, based on experience, this is false. Most instances of weak ignitions have been on shain saws, I will say, but numerous have been on 4-strokers, whether they be breaker-ignition or electronic. But how often do we see points & condensors these days...heck, I don't think I've seen a set in 10 years or so...except maybe on some old Ariens snowthrowers here and there.

South, what I'm getting at is don't rule out the ignition as a potential source of trouble until properly tested.

 
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04-30-04, 08:34 AM   #15  
south
The saga continues...

I replaced all fuel lines and feul filter...Fired it up and ran for approx. 15 minutes before the sputtering began. The 'good' run time is really random now.

The engine is a Kohler Magnum 12 Model M12T

I also pulled the adjustment screw out of the top of the carb and sprayed some carb cleaner in the port. Just want to verify I did this right. I first turn the screw in until it bottomed out (just snug), which took two full turns. I then removed the screw and sprayed the cleaner. I reinstalled the screw and bottomed it out (just snug), then backed it off two full turns. I did not take the carb bowl off, as I wanted to elminate the fuel lines and filter as the culprit.

I am leaning toward the replacing the coil and the plug wire. Any diagrams available on where it is located and how to get the old out and the new in.

Thanks to all...

 
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04-30-04, 10:43 PM   #16  
Engine Power Loss

You can goto the Kholer website at http://www.kohlerengines.com.Once there click on "repair manuals" and click on your models book.It's a long download tho (around 15MB.)

But to answer your question (at lest partly) the coil is located under the shroud (the cover on front of your engine that says "KOHLER MAGNUM 8Hp".
You might have to take the air filter cover off,and I think there's a bolt under the fuel tank too.These engine manufactors are notorious about hiding bolts,nuts and screws anymore.

Hope that helps

 
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05-01-04, 12:36 PM   #17  
M12t

South,
On the same tag you found the Model (M12T) you will find the spec. and serial #'s. What are these numbers? With these, I can provide a part number for the armature (coil), which by the way includes the wire on this model. Follow repair_guy's steps to get at it. Also, the correct air gap between the coil and the magnets on the flywheel is .012"-.016" and the correct spark plug is a Champion H10C. Post back with the engine #'s.

 
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05-03-04, 12:02 AM   #18  
Before doing any replacing parts, pull the carb bowl off. If you haven't done this, you need to. It sounds like there's water and or rust/debris in there.


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05-06-04, 06:59 AM   #19  
south
Ignition Coil

Well I replaced the ignition coil and that has fixed the problem. I dont know why I didn't suspect this in the first place as I just replaced plug wires on a 75 chevy because it was doing the same thing.

thanks for all the advise and suggestions...

South

 
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05-06-04, 09:55 AM   #20  
I am glad you got it fixed. I knew it was the coil.

 
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05-07-04, 12:35 AM   #21  
Glad you got it fixed! That coil failed in a peculiar manner in comparison to the majority of coil failures I see. Usually the failure is temperature related, or just total and complete failure to produce any spark. Every now and then one does some "funny stuff" . Thanks for letting us know how it went!


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05-24-04, 05:40 PM   #22  
south
Just got back around to posting...

After about 15 minutes into the second cutting with the new coil, the engine starting running rough, I pulled the bowl off the carb and found a number of small black 'rock' like particles in the bowl. I cleaned the bowl, pulled the needle valve and cleaned all the ports with carb cleaner. Put it all back together and it has run for 2 weeks without a sputter.

Just thought you all should know...thanks for all the advice and input...and for saving me a few dollars...

South

 
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05-24-04, 11:12 PM   #23  
LOL!!! I sure thought it was a fuel problem! Thanks for letting us know!


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