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20HP B&S engine that stalls under load


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11-05-07, 05:27 AM   #1  
20HP B&S engine that stalls under load

I have a B&S 20 HP Twin inline, model 460707.

My engine started stalling out and dieing when I engage the blade or drive up a slight grade. The engine sounds like it's missing.

When I checked the air clearer, I noticed that one of the wing nuts was loose and some dust had made it's way past the air cleaner. Couldn't have been that way very long, there wasn't much dust past the air clearer and I had just cleaned it a couple of weeks before.

I've since changed air clearer and pre filter, new carburetor kit (cleaned the carburetor, even soaked it 36 hours in Napa's# 6402), float, spark plugs, and a fuel filter. I've pulled the fly wheel and the flywheel key looks flat. Compression was over 90psi in both cylinders.

The vent hole in the gas cab seems to be clear.

I'm getting good spark, using a grounded screwdriver. When I draw a spark the engine speed drops about the same for both cylinders.

It doesn't completely stall out and die now that I've done all this work, but it now boggs down and lacks power when I engage the blade. I back off and it takes more time to come back up to speed than it should.

At this point, I'm at a loss for what to try next.
Can you suggest something else to try?
I haven't changed the fuel lines, but that's something I've been thinking about doing.
At what point should I pull the heads and clean any deposits?

Thanks,
-=Carey

 
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11-05-07, 06:14 AM   #2  
Make sure the fuel line is not resting on top of the governor/throttle linkage, intefering with the action.
I've worked on half a dozen Briggs twins this summer and have to be sure governor/throttle is free of debris and I always put a drop of 3-n-1 oil on linkage pivot points.
36 hours dip time is a bit much, good carb dips shouldn't take more than an hour.
What was condition of old spark plugs?? clean light brown/gray??
what is condition of new plugs after running for a while?
just hope internal governor parts are not malfunctioning.
thanks,

 
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11-05-07, 09:27 AM   #3  
To isolate it as an engine problem, disconnect the "kill"
wire at the terminal on the front of the engine and start,
but you will have to choke it, or ground that terminal to shut it down. If the engine runs good with it disconnected, then look for grounding/shorting around the seat switch area,
especially if it is an mtd, or if the wire to the neutral switch is just hanging around near metal. These faults are easy to spot when it is almost dark, so maybe the time change will come in handy.

Fish

 
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11-05-07, 08:14 PM   #4  
I'd suspect ignition problems, but try running it on half choke to see if it improves.


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11-06-07, 05:09 AM   #5  
Throttle linkage, choke, and kill switch wires

Thanks for all the replies to this.

I suspected the throttle linkage, so I had my son drive and I watched the linkage. When it bogged down, the throttle was wide open.

The old spark plugs were black. Wasn't surprised by them, they had been in there a while.
I'll look at the new plugs tonight. They have less than an hour on them, but that could lead me to some answers.

I've tried pulling the choke out a little when it starts to stall, and the speed just drops even more.

I haven't checked the kill switch wiring. That should be easy enough to check, but the engine runs fine until I start to load the engine.

 
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11-06-07, 06:33 AM   #6  
Sounds like engine is running in an over-rich condition. Your new plugs will be black after 5 mins of run time.
Your idea of removing heads and cleaning deposits is not a bad one.
Wouldn't hurt to check tappet clearance either. .004-.006 for intakes, and .007-.009 for exhausts. Piston down 1/4 inch from TDC on compression stroke of cylinder checked.
I know, it will take some work.
thanks,

 
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11-06-07, 10:07 AM   #7  
Posted By: carey313 but the engine runs fine until I start to load the engine.
I had a customer that brought me a tractor, and he told me he had a deck spindle going out as it was bogging his engine down, and wanted to know when I could fix it. I said I had the spindles, but taking a quick look, I told him that the
spindles felt ok, but he was very insistant. While he was in the store, I dropped the belt off of the engine pulley and lowered the deck, and yes his spindles were fine.
When he came back out, I told him that the spindles were
fine. He got angry, said something rude. Got on the tractor
and started it up, engaged the blades, and the engine started bogging down. "See!!!!".
He got real mad because I couldn't stop laughing when I told him the belt wasn't even on the engine pulley.

He turned red, and left the mower with me so I could
fix the problem, it didn't take long. The two terminals
of the seat switch were so close together that the spark/arc was jumping the gap, and only did that when the pto switch was activated while the engine was running.

That was a MTD, what brand is yours?

 
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11-06-07, 12:37 PM   #8  
Mower brand

It's a Murry, as bad if not worse than MTD.

 
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11-06-07, 06:28 PM   #9  
I suggest using a spark tester to see how strong your ignition is. These engines are propably the ones I change coils on the most...so I don't have much problem pointing my finger at the coil when problems like this arise. It does sound like weak spark, especially after all the other things you've done.


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11-06-07, 09:18 PM   #10  
Never used a spark tester.

Where do I get a spark tester and how do I use it? I've changed out the coil twice on this mower, I know what you mean. Both times, I couldn't draw much of a spark with my screwdriver test. With this coil, I draw a spark a good inch or more. I forget how many Kv it takes to draw an arch an inch?

btw: The new plugs are clean. One had some gas on it, but that was it.

 
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11-06-07, 11:57 PM   #11  
If you're getting a 1" spark, your coil should be ok. I'd revert to carb problems then, possibly the choke not opening fully? Or the mixture screw backed out too far? (if equipped).


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11-07-07, 05:58 AM   #12  
Carb problem?

After all that I've done with the carb, I think I'm ready to rule out the carb as the problem. The choke is full open, no adjustment for anything on this carb. It's clean and has a new float and kit.

What should I have for compression on this engine? If I'm getting a good compression, does it mean the valves are fine or should I still consider cleaning any deposits on them.

I still need to try disconnecting the kill wire and running it. I have another problem to fix now, last time I had it running I hit a fire-ant mound and bent the blade. Need to replace that now too.,. Bummer, I hate those little ants. Haven't found anything that gets rid of them, they keep coming back and building mounds.

 
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11-07-07, 03:13 PM   #13  
I suppose it could be valve related, but It doesn't sound like a valve problem, or a carbon deposit problem either. I'll second the motion on disconnecting the kill wire and trying it in case there's a high-resistance short in a safety switch or something. That is rare, but could cause your problem. Another thing is that you might try new plugs again. I've had bad ones, and sometimes a new bad plug will make you pull your hair out...until you try another new plug. Sometimes the insulator can come loose in the plug, and slide back and forth on the electrode, causing misfires.


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11-07-07, 05:23 PM   #14  
Bad spark plugs.

I agree with the bad spark plugs, I've had that problem with my car. I've cleaned up the old plugs and put them in before I started this thread, didn't see any change. I'll pick up a new set next time I'm by the store anyway.
Thanks,
-=C

 
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11-08-07, 03:15 AM   #15  
I love a good mystery, am anxious to see solution to this problem,
while we're all mulling over what's transpired thus far, can you give me the type and code of your engine and what inch cut your Murray unit is ?? Is it a Garden Tractor or Lawn Tractor, from this I can find what your mower model number is.
Thanks,
P.S. Your post stating one plug was ok but the other was wet may be a clue.

 
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11-08-07, 05:04 AM   #16  
B&S model 460707

Its a 42" cut murray lawn tractor.

B&S 460707 code 0001055A type 2278E1

If gas on the spark plug is a clue, then let me give you another clue.
I also see gas in the intake manafold when I remove the carb.
I almost always get a loud pop if I don't choke the engine when I kill it. I pull the choke to get the engine speed down before I kill it, so there is probably excess fuel in the cylinder that didn't get burned.

 
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11-08-07, 08:57 AM   #17  
Thanks,
Since the engine was assembled Jan. 5, 2000, I'm assuming it's a 2000 Murray model, has foot pedal hydro, probably a Peerless VST, maybe VST 205-02nnnnnnn, Murray in 2000 had enuf variations to have 31 model numbers for this 42", and the fuel pump had 4 screws, vs 3
all unimportant.
In trying to summarize what's transpired in this thread before, can we assume:
1- coil is good and properly gapped, .010 would be good
2- plugs are good
3- flywheel key is good
4- governor linkage is unrestricted and moving freely
5- governor linage has not been disturbed for any reason??
6- Fish's idea(a good one) on seat switch ruled out.
7- choke plate fully open after warm up
8- used correct gasket from carb kit 694056, there's 4-5
9- carb float at correct height before re-assembly
10-governor linkage operates when coming under load
11- Anything else ??

Now, in my experience with Briggs twins:
1) I've found bottom of intake manifold wet as well, stuffing paper towel down it, it was never excessive, just excess fuel from being choked at startup, I believe.
2) I've never had a Briggs twin pop at shutdown, like some others I have do, this is turning key off but having compression to ignite mixture w/o benefit of spark.
which is a clue to having carbon buildup in one of the cylinders, which might be the one with the wet plug.
QUESTIONs:
1) When the engine begins to stumble when load is applied, does it emit any black smoke ?? or not??
2) Why are you having to apply choke to slow it down before you kill it ?? (Introducing this extra fuel might be reason it pops)
3) Is the idle jet in carb the adjustable one with spring, or the one you just screw all the way in?? (just curious)
PARTING THOT:
When throttle is opened, fuel is drawn thru all passages, idle and main, could it be that when carb was put in dip, air was trapped in idle passages and they're still restricted ??

I'm exhausted...
Thanks,

 
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11-08-07, 07:29 PM   #18  
Summary of problem

Thanks For all the advice from all.

Since the engine was assembled Jan. 5, 2000, I'm assuming it's a 2000 Murray model, has foot pedal hydro, probably a Peerless VST, maybe VST 205-02nnnnnnn, Murray in 2000 had enuf variations to have 31 model numbers for this 42", and the fuel pump had 4 screws, vs 3
all unimportant.
>But it all sounds right

In trying to summarize what's transpired in this thread before, can we assume:
1- coil is good and properly gapped, .010 would be good
>Gapped when it was installed, have not checked, I could do that.

2- plugs are good
> Yes
3- flywheel key is good
> Yes
4- governor linkage is unrestricted and moving freely
> Yes
5- governor linage has not been disturbed for any reason??
>Only thing that I'm concerned about is the piece that is right at the carb, I bent it when I put the carb back instead of removing the carb and installing it right. It doesn't seem to be restricted though.
6- Fish's idea(a good one) on seat switch ruled out.
>Not ruled out yet, but it will be.
7- choke plate fully open after warm up
>Manual choke, properly adjusted when the carb was re-installed.
8- used correct gasket from carb kit 694056, there's 4-5
>Fairly sure it was the right kit.
9- carb float at correct height before re-assembly
>Didn't see any adjustment for the float height.
10-governor linkage operates when coming under load
>Yes, when there is a load, the carb opens up fully.
11- Anything else ??
> I suspect some build up in the cylinders since this started with a slight leak at the air filter.

Now, in my experience with Briggs twins:
1) I've found bottom of intake manifold wet as well, stuffing paper towel down it, it was never excessive, just excess fuel from being choked at startup, I believe.
>I've never seen this, but then I don't work on mowers everyday, only when I have a problem. I figured it was probably because I choked it to kill it.
2) I've never had a Briggs twin pop at shutdown, like some others I have do, this is turning key off but having compression to ignite mixture w/o benefit of spark.
which is a clue to having carbon buildup in one of the cylinders, which might be the one with the wet plug.
> Sounds about right, the pop didn't start until the 3rd or 4th season. This is probably a sign that the carbon build up has been getting worse. Should have read this sign.
QUESTIONs:
1) When the engine begins to stumble when load is applied, does it emit any black smoke ?? or not??
>Only smoke I've noticed is when it first starts from the cold start. Figured it was because I don't push the choke back in fast enough. No other smoke that I've seen.
2) Why are you having to apply choke to slow it down before you kill it ?? (Introducing this extra fuel might be reason it pops)
>Just to prevent the pop. I choke it until it almost dies.
Thinking about adding a fuel shut off valve.

3) Is the idle jet in carb the adjustable one with spring, or the one you just screw all the way in?? (just curious)
>The carb doesn't have any adjustments that I can see.
PARTING THOT:
When throttle is opened, fuel is drawn thru all passages, idle and main, could it be that when carb was put in dip, air was trapped in idle passages and they're still restricted ??
>The Dip was because of a suggestion on this thread. I had cleaned the carb with spray can of Berrymans B12 and though that would be enough. The original problem was that the engine would die, after the carb rebuild the engine would bog down, but didn't just die anymore. Thought the dip would help, but it didn't help.
>The bare wire rubbing against some metal still seems to be a possible problem. I need to look at the kill wire.

I'm exhausted...
Thanks,
>I've had a long day too. Thanks for the summary and thoughts. Hopefully I'll have some good news with the solution to this mystery some time this weekend.

Good night to all.
-=Carey

 
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11-09-07, 06:10 AM   #19  
Response to Post #18

Rather than include previous post, will just refer to it.
Corrections on my part, 1) Assumption 8, kit would be 693501, 2) Assumption 9, probably a plastic float, 3) question 3, since this is last of Briggs L-Head twins, Briggs carb has progressed to having no idle adjustment.
Note: soaking in carb dip is never bad idea, as well as blowing out passages with carb cleaner spray and compresssed air.
Now,
What's caught my eye in post 18, is the forthright answer to assumption 5
the governor/throttle relationship has been disturbed.
Carey, 1 - did the short throttle link rod get bent, or, the piece affixed to end of throttle shaft on carb the link twists into, get bent ?? 2 - does the engine idle faster than it used to ??
Regardless, a static readjustment of governor/throttle mechanism could only help.

Cheese, Puey61, any skilled technician, don't be shy about chiming in here.
Thanks,

 
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11-09-07, 07:31 AM   #20  
Assumptions

Sorry about that, Wanted to get the summary replies to the top for anyone that is looking at this thread.
1. kit was 693501
2. Float is plastic
3. Agree, soak is good idea. Spray carb cleaner after soak.
4. Just bent the end of the last link to the carb to place it back on without removing the carb.
5.I think it was faster idle than before the last time I put it together.,. I need to look a that last link again.
6. Any advice on how to do a static re-adjust. Understand the basic funtion of the governor, but I think the only part that might be wrong is the link between the carb and the linkage. The governor seems to be working, but I might have the last link bent at the wrong angle or something.
7. When I had my son drive and I watched the governor, the carb throttle was open full when the engine was under load. The speed still dropped more than it should or doesn't seem to have the power it should.

Headed out for the morning, I'll work on the mower more this afternoon/evening.

Have a good day,
Cheers,
-=Carey

 
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11-09-07, 10:36 AM   #21  
Ok, here's what I'd prefer you'd do, order a new throttle link, it's part # 693544, it's different from the one that's used on the older 3 screw carbs(# of screws attaching fuel pump ass'y to carb body) and it costs $1.40, Briggs retail.

I've never had any luck trying to adjust compensating for bent stuff, these parts are precisely engineered, even the angle of the dangle of the hook on the end of the link, could be that bending the end of the link has introduced some slop in the overall scheme of things.

Static governor adjustment is fairly simple:
1) Disconnect throttle control cable from governor mechanism
2) Beginning facing front of engine, move around to your left, looking at engine from the side
3) Find the 7/16 th nut, this tightens clamp of governor mechanism to the governor shaft coming out from the inside of the engine. It may be fairly close to the muffler guard on your model. Loosen it several turns.
4) Rotate the governor mechanism such that it opens throttle to wide open. CCW
5) The internal governor shaft that protrudes to outside this mechanism now rotates on, has a slot in the end, this is for to put a screwdriver, and turn it CCW as far as it will go.
6) Holding the shaft and governor mechanism in these positions, tighten the nut on the clamp.
7) Reattach throttle control cable.

Last question: after start and warmup, does a fast throttle-up work pretty good ??
thanks,

 
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11-10-07, 05:25 AM   #22  
I've been following this thread and you're all doing just fine. Here are my concerns: 1- The potential for a parasitic load problem causing the trouble. Begin by removing the blade drive belt at the engine and running the engine (and trans) through its paces. As you normally would only that you'll have no cutting action...Throttle up, throttle down, drive the mower up and down hills. In other words, go about your mowing without cutting. 2- Ignition strength, this has yet to be addressed. Go to your local small engine shop and purchase two inline spark testers (I like Briggs part number 19368, but Tecumseh and Kohler have ones that work just fine) and install these between each spark plug and spark plug lead wire. Fire up the engine, set the parking brake (so you can get off the seat and have the engine continue to run) and watch the spark in each tester window and look for any intermittancy or lack of spark on each cylinder. Be sure to allow enough run time for the engine to get up to full operating temperature to get acurate test results. 3- Engine ingestion of contaminents, by way of your loose air filter. Even if you suspect that not enough time elapsed for any sustained damage from the loose wingnut on the air filter I'd still pull each cylinder head off and inspect the condition of each combustion chamber paying particular attention to the valve train with an emphesis on the valve clearances.

 
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11-10-07, 08:41 AM   #23  
Still the simplest first thing to do is to disconnect the
kill wire to the coil and start the mower and use it. If the problem is no longer there, then the problem is in the tractor's wiring or switches.
As you are looking at the engine from the front, with the air filter closest to you, look for a solitary wire going into
the engine shroud just to the left of the carb, and simply
unplug it. I am assuming you have left the hood off, so it is
real easy to find. The alternator wires go in behind the carb.

Please try this before spending a lot of money on anything.

BTW, if your symptoms occured when going up hills, or down
or cornering or braking, it would sound like you had a layer
of water in the bottom of the carb, but with all you have done and checked, this sounds more like an ignition grounding
I might even suggest you remove the top shroud and check
the wiring under there, a mouse chewed wire near metal
might do the same thing.

Remember, do the simple and cheap things first.

Fish

 
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11-12-07, 06:57 PM   #24  
Spark tester.

I took the belt loose and disconnected the kill wire. Neither seemed to do anything for this problem.

Hey puey61,

I bought a spark tester today. $18 for a neon bulb, a glass tube, heat shink tubing, and some spark plug wire. Sounded expensive, but I got the only one they had in stock.

I hooked it to the first plug and it was fine, thinking that the wires were one, I thought it was as waste of money, then I tried the other plug and it is dead, checked the connections and sure enough, it's dead. This is the plug with the gas on it earlier.

My shade tree training just went out the door. Looks like I need to replace the coil for the third time, or is that 4? Any suggestions on a better replacement or any reason that these keep going out? Seem to last about 2 years.

Probably won't get it changed until this weekend, but wanted to update this thread with the latest.

Thanks,
-=Carey

 
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11-12-07, 08:37 PM   #25  
You get a 1" spark from the wire, but it won't work with the spark tester?

I suggest replacing it with an original Briggs coil instead of aftermarket if you aren't already. Heat will cause these coils to go bad. Pull the tins off the cylinders (especially the tin that covers the bottom side of the cylinders) and clean out the cooling fins on the cylinders. It may be getting too hot for the coil. If the cooling fins are plugged, you may also drop a valve seat or incurr other internal engine damage as well.


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11-13-07, 02:11 AM   #26  
In each of the previous ignition coil replacements, have you installed a genuine Briggs & Stratton coil? Have you at any point replaced the ignition key switch? Have you ever had any trouble with battery charging, in other words, frequent battery replacement?

 
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11-13-07, 05:19 AM   #27  
I've never had trouble with the key switch.
The old battery lasted 4 years, this one is 2 years or so old and doesn't seem to have a problem.
All coils have been B&S.
Not sure if the last one fixed the problem, I put the old one in the box and put it on the shelf as if it might still be good, Just can't remember now what the problem was.

I need to verify that I can still draw a spark on the dead plug. Still trying to figure out what happened to my shade tree knowledge and why I missed this.

I'll look at removing the tin, but not sure it's a good idea if these help keep the fins from getting clogged. I think the air is pulled if from the top and blows across the coil and down across the fins. Maybe I need a high rise hood scoop to pull in air from higher above the engine. It would look like I had more power under the hood too. =)

 
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11-13-07, 06:09 AM   #28  
If you have continuing problems with the coils, you need to check your kill wire for voltage, any voltage will damage
the coil, partial voltage will do it slowly over time.
I had one that would act off and on, kind of like the mower you have now. Sometimes both sides would fire, sometimes only one. Before finally figuring it out, and putting on a new coil, I checked for voltage, it showed
2-3 volts. I found a couple of frayed wires in the harness that were close to each other as the cause.

Fish

 
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11-13-07, 07:16 PM   #29  
Yeah, I think that's where Puey61 was heading with the questions about the keyswitch and charging system operation.

Full 12 volts will kill the coil quickly. If it's just a quick zap for a few milliseconds, (like a bad keyswitch could possibly do), it wouldn't ruin the coil immediately, but rather over time. So would the low voltage Fish described. I'd check that for sure. There should never be any voltage present on the kill wire from the mower.


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11-14-07, 03:33 AM   #30  
I would replace the keyswitch just to be sure that this is not a potential problem for what little it costs. Post back with your mower's chassis ID numbers, I can then provide you with the Murray part number for the switch. The ignition coil is Briggs part number 397891.

 
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11-14-07, 05:31 AM   #31  
Kill Wire Monitor

Morning,

How long would you expect the coil to last?

Is the key switch open or is it a ground connection or grounded to kill the mower? Should I monitor it with it connected to the coil or am I only looking for a voltage from the switch/mower side?

I'll look at it and set up a monitor while it's running and bouncing across a few bumps. My meter has a min/max monitor feature, so I just need to find a way to secure a connection to the wire and ground. Checking this is a good idea, and easy enough to verify.

The mower is a Murray model 42572X8A.
What's the number for the plastic dash? This one is busted in several places, only a cosmetic repair, but I'd consider replacing if it if I replace the switch.

Thanks,
-=Carey

 
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11-14-07, 07:29 PM   #32  
I had a typo in my previous post, the correct part number for the coil is 394891, not 397***. The ignition switch is Murray part number 092377MA and the dash is 776190MA. To test for voltage to the coil through the kill wire, locate the junction block of the kill circuit at or relatively near the speed control/governor bracket that includes the single black wire going to the coil. With the engine shut off but the key in the run position and your 12V DC test meter grounded anywhere on the engine and the positive test wire clamped to the junction block, you should get no reading whatsoever. Make sure that all implements are disengaged and the parking brake is set before performing the test.

 
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11-14-07, 08:01 PM   #33  
Thanks for the updated part numbers.
I had a coil on the shelf from a previous repair attempt, that turned out to not be the coil. I installed it tonight and both plugs have a light on the tester. Took it for a test drive and it didn't bog down on the tiny hill I have, but I have not put the belt back on from the other day so I didn't get to try cutting some grass. Saved that for tomorrows addition.

Monitored the kill wire tonight. max voltage was 50mV (That's zero on most meters). I don't think it is the switch and apparently I've only needed 2 coils in 6 years since the other one was ok.

btw, The screw driver test didn't have a spark on that plug today. I know it did before and the engine speed dropped with both plugs. That's confusing me. Probably fixed the original problem with the carb kit/float, and the coil went out somewhere along the way. The original problem was the engine would just die. After the carb kit, and new spark plugs the engine didn't have power, but it didn't die anymore.

Cheers,
-=Carey

 
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11-14-07, 10:42 PM   #34  
Sounds like you've got it whipped. Glad you got it. Sometimes these little engines can be sneaky, trying their best not to get fixed, hehe.


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God bless!

 
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11-21-07, 08:43 AM   #35  
Summary of problem

Hi,
Wanted to tell everyone Thanks for all the help.

Here's a summary of this thread:

Original problem, the engine would die and seemed to lack power. Had a good spark on both plugs, changed the spark plugs, then the rebuilt the carburator.
This original problem was probably fixed with the new float and cleaning the carburator.

After the carb was installed, the mower still lacked power, but didn't die anymore. At this point, one of the plugs didn't have a spark (although I didn't check it again right away so we tried several other things first ).

Changed the coil and the problem is fixed. I inspected the old coil and I see pin holes in the plug wires at the point that the wires run through the tin sides of the engine. I plan to drill the holes in the tin side out and put in rubber gromics to prevent this problem in the future. Moving the plug wires when I replaced the plug wires probabaly moved the pin holes away from the tin and I had good sparks then I moved the wires again and the pin holes aligned back with the tin side and there was no spark.

Thanks for all the good advice.

Cheers,
-=Carey

 
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11-21-07, 09:42 AM   #36  
Thanks for the feedback

Glad you found the problem. There is no clearance under the backplate under the flywheel and the tin breather backplate to route the wires comfortably. Maybe the one wet plug you had at one point was a clue.
thanks again,

 
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11-22-07, 03:55 PM   #37  
Phew, and we got this one solved in under forty posts! Good work everyone and congratulations carey313. I'm still concerned about the reading of voltage, albeit miniscule, at the kill wire...replace the key switch just to be safe, it costs fairly little.

 
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