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B&S 18hp - won't restart when hot


Monty NC's Avatar
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03-24-07, 05:24 PM   #1  
B&S 18hp - won't restart when hot

I'm starting a new thread, because I have a different question. Background: I recently picked up a used 10 year old MTD lawn tractor with a 18.5 hp Briggs & Stratton TwinII I/C engine (model 42A707). I have replaced the fuel & air filter, both spark plugs, and changed the oil & gas. I also did a complete carburetor rebuild, including the fuel pump membranes/gasket.

It runs OK, but when I shut it off I can't crank it again for a couple of hours. It turns fine and may sputter a time or two, but it won't fire up again until it's completely cooled off. I pulled a spark plug to look at it, and I don't believe it's flooding. A search here turned up the armature as a possible problem - does that sound right? How do I check that? Or is there anything else that might cause this problem?

Thanks again for this great site.

 
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03-24-07, 05:58 PM   #2  
sounds like ignition coil problems to me.Thats the way they does.They start braking down and when the engine gets hot the coil quits working.And wont restart until the engine cools off.A new ignition coil is gona run you about $52.00 give or take a dollor.

 
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03-24-07, 06:15 PM   #3  
Azis
I think this may tie into your previous thread and indicate to me that low compression could be the cause. Valve clearances could be partial cause, enough to cause the no start. Make sure all the cooling fins are clean also.
What color were the spark plugs?
Check for spark when its hot and won't start, if you have spark then the coil is prolly not it.

 
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03-24-07, 06:26 PM   #4  
Thanks for the responses. The cooling fins are clear and I can feel the air blowing from the side of the motor. The spark plugs were sort of dirty gray color, but you could still see the white (porcelain?) of the center post. Guess I'll have to get a spark tester and see if the coil is the problem. How do you differentiate between a problem with the coil vs. a problem with the armature?

I should add - this evening I was running the mower at operating speed and the thing shut off - it quit just as if I had switched off the key. No smoke, no sputtering, no backfire, just cut off and of course wouldn't restart. Does this give any clues?

I'm hoping for something simple, because I have no experience with things like compression & valve clearance... although I can tackle that if I have to.

Thanks again for the guidance.

 
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03-24-07, 06:31 PM   #5  
Monty,
I think checking out the coil is the first thing to do.
B&S riding lawnmowers have been known to simply stop for no apparent reason after running around a half an hour. It's been found that the engines are vapor locking. If your coil checks out to be ok, check this out next!

CD

 
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03-25-07, 12:27 AM   #6  
I'd bet a dollar to a donut that your coil is bad. The coil and the armature are basically one and the same on this mower. This is an especially common failure on the twin cylinder flatheads like yours. Check for spark next time it quits and I bet there won't be any. If not, replace the coil.


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03-25-07, 05:24 AM   #7  
Posted By: cheese The coil and the armature are basically one and the same on this mower.


Ahhh - that explains my confusion (at least part of it). I thought that the thing my parts list shows as "armature - magneto" (part No 394891) was the armature -- the horseshoe shaped thing right next to the flywheel. What you're all referring to, my parts list calls the "armature - starter" (No 544 on the diagram, looks like I'll have to measure the housing length to get the right part number). Do both parts have to be replaced? The magneto looks rusty (as does the flywheel in some places). I'm really getting an education here!

 
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03-25-07, 06:04 AM   #8  
Azis
You need to also post the rest of the engine numbers to help discern the correct part. They are the Model # Type # and Code #. The IPL should reference before/after code XXXXXXX if multiple parts are used on the same model.

The IPL I am looking at shows Ref # 544 as the armature-starter, this is part of your starter and NOT what ne of us are refering to. Ref # 333, part #394891 is the Magneto/coil (magnetron) that we are reffering to.

You should knock off any large accumulations of rust and clean the area on the flywheel that will pass by the coil in order to set and maintain proper clearance. The rust will not affect the coils operation as long as the air gap is set properly.

 
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03-25-07, 08:22 AM   #9  
Gotcha. I guess I was confused by the fact that they were both labeled armature... a little knowledge is dangerous. FWIW, here's the rest of the numbers from my motor:

Model 42A707
Type 123801
Code 9702035B

I'll pick up a spark tester and check out the coil. Thanks again!

 
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03-25-07, 08:32 AM   #10  
Azis
If you have some sort of jumper lead you can use the current or an extra spark plug.
With a jumper (jumper cables will work) connect one end to the threaded or hex part of the plug and the other end to a solid ground on the mower. Crank the engine and look for spark.
You can also hold the plug against the block of the engine while cranking.

Edit: Forgot to mention that one of the high tension leads needs to be connected to the spark plug being tested.

 
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03-26-07, 05:37 PM   #11  
I did the spark test, and I couldn't really tell any problems. I started the engine, and let it warm up. Then I shut it off and of course it would not restart. Tested both spark plug wires with the crude gap test and I saw sparks with both wires. I just held the end of the spark plug wire close to the block for this test - if I need to be more precise than this let me know. I don't mind replacing the coil, but I would like to rule out other problems (if possible) before I buy another part...

 
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03-26-07, 06:05 PM   #12  
Azis
If you have spark then the coil is putting out.
You can check fuel next since we must assume there is sufficient spark. Try a few drops of fuel in the carb when it wont start.

 
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03-27-07, 05:44 PM   #13  
Gas in the carb = no go. Checked for spark again in both spark plug leads and again I saw spark on both sides.

Another observation: I cut about half the front yard today and then the mower started skipping like it was running out of gas, and after a few times of this it quit.... and wouldn't restart. I noticed that the fuel filter looked almost empty - just a small amount of gas down in the bottom, none making it to the outflow tubing. Is this what is meant by "vapor lock"? When I took the gas tubing off the fuel pump it flows freely - no way the motor uses fuel THAT fast. (By the way, I had loosened the gas tank cap, based on something I read in a thread here somewhere) Just to be sure I didn't screw up the fuel pump, I took it back apart and the membranes seemed OK -- didn't seem out of position, springs were all in proper place.

This is getting worse instead of better - it used to stay running long enough for me to cut the yard. I've got to do something quick - the front yard looks kind of funny right now...

 
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03-28-07, 06:34 AM   #14  
Azis
Here is where things start to get a bit gray, I personally have not experienced this scenario myself, so maybe those with more hands on will have some ideas.
I do think I recall hearing about some briggs having problems with vapor lock, which is basically an air or vapor pocket that gets trapped in a high point in the fuel system which the fuel can not pass.
I would certainly try to confirm that you are getting fuel to the cylinder along with spark. Since it does run we can rule out timing, and since we have fuel and spark the only thing left is compression.
You might try a few drops of fuel in the spark plug holes and see if it tries to fire at all.
Does the engine spin easily by hand?

 
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03-28-07, 07:54 AM   #15  
Posted By: Azis
Does the engine spin easily by hand?
Yes, and I checked compression in both cylinders. It reads about 100 on one side and 110 on the other, and takes about 3 cycles to get to 90 then goes up to max over the 2-3 cycles.

 
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03-28-07, 08:18 AM   #16  
Azis
I am still leaning toward valve clearance at this point. This is not very hard to check or correct If your clearances are at a minimum when cold, when the engine is hot and parts expand clearances deminish.
If you refer to the drawing on page 2 ref item# 551-valve cover. This is what you will need to remove to access and measure the valve clearance.
If you have a feeler gage and are up to trying yourself we can walk u thru at least checking...?

 
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03-29-07, 10:22 AM   #17  
I appreciate the offer. I'm not sure I have the confidence to go that route at this point. I'm just afraid I'm either missing some really simple (stupid) or it's more complicated than I want to tackle.

I changed the oil one more time (just in case there was some gas in it, although I couldn't smell any), and then I decided that I would load it back on the truck if it sputtered again. It did, so I did. There is a local shop with a good reputation, so we'll see what they find. Thanks again for all the help.

 
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03-29-07, 10:34 AM   #18  
Azis
It would be most interesting to see what they come up with
I do think it is a compression issue at this point and since you don't mention it smoking excessivley, I would go with the valve clearances

 
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04-02-07, 12:41 PM   #19  
Any updates?
I have the same problem with my 19.5 HP B&S.
I just ordered a carb overhaul kit and a mag....

 
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04-02-07, 12:49 PM   #20  
Azis
Have you checked for spark and fuel when it quits?

 
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04-02-07, 01:06 PM   #21  
As for Monty NC's problem...

When my B+S 18 twin behaved much like yours is, the vacuum (or fuel pump) hose had sucked it self shut because someone had used cheap fuel line; when the engine heats up, the hose becomes pliable and sucks shut. When the engine cools, the hose stiffens up for a while.

If that is your problem I would replace the hose with a strong reinforced hose and use hose clamps to secure it.

 
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04-02-07, 01:11 PM   #22  
Azis
Posted By: Monty NC Gas in the carb = no go.
This should eliminate the fuel line as the problem.

 
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04-02-07, 06:22 PM   #23  
I am getting plenty of fuel.
Maybe too much...after trying to start it repeatedly, I can look down the carb and see a pool of fuel.
As for spark...when cool it is a sharp snap of blue....when hot it is a click of orange...so I believe that I am on track with replacing the mag.
Also when I pull the plugs after trying to start it over and over...the plugs were fuel fowled.

I had already decided the carb needed to be overhauled...mainly due to the amount of choke necessary to keep the engine running. Unfortunaly I recieved a e-mail today stating that the overhaul kit was backordered due to the carb type....I have a 3 screw fuel pump...this has been replaced by a 4 screw fuel pump....sigh...
For $117, I can purchase a new carb (4screw), and at least be able to get replacement parts in the future.

My mower is a Craftsman mod 917.256571
B&S mod 42A707
Type 1624 01
Code 9604195B

 
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04-02-07, 06:33 PM   #24  
Azis
You should still be able to get the 3 screw carb and fuel pump kit.
It does sound like your coil could be failing under compression. I think your on the right track with yours. Fuel in the carb and fuel wet plugs.
You can ohm out the coil and if its getting weak it may well show bad. I think a good one should read between 3k and 12k ohms. Even if it reads good, it can still be bad. But if out its most likely bad.

 
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04-03-07, 02:21 PM   #25  
I was the coil. Dang it.




Thanks again, all, especially Az for stickin' it out with me. (Cheese, I'd buy you that donut... except I can't afford it now! )

 
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04-03-07, 03:23 PM   #26  
Azis
Posted By: Azis If you have spark then the coil is putting out.
You can check fuel next since we must assume there is sufficient spark. Try a few drops of fuel in the carb when it wont start.
Well glad you got it at least. The only Absolute test for the coil is to replace it with a KNOWN good one.
Happy Mowing

 
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04-03-07, 10:40 PM   #27  
Glad you got it Monty. Thanks for the update.


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04-04-07, 10:42 AM   #28  
Azis
cheese,
Curious if these twin briggs are the only common occurance of these symptoms and remedy.
I have had a couple kawasaki on Deere's with the same symptom, however a valve job was the cure for them.
In this case had you not had an available spare coil to test with, what else would you have done to warrant buying a $40+ non returnable part simply cuz nothing else shows bad?
I also have a kohler on a cadet that shows similar symptoms. However it will sometimes restart or at least try much sooner after it dies. I have looked at it a few times but not had it in my shop yet, but will this week. I can't remember all I have done with it but, I do recall getting to the point of blaming the fuel pump.

TIA
Appreciate your time and experience

 
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04-04-07, 08:28 PM   #29  
On the briggs opposed twin cylinder engines (opposed only..not V-twins), it is very common for the coil to go bad. If one of these engines runs fine, but shuts off and won't restart when hot, but restarts fine after cooling...I don't even check anything...I just replace the coil. I've seen so many of them that I just know that's what's wrong...it always is.

I've seen some Kawasakis that had that particular problem with the valve issues. Mainly flatheads with hundreds of hours on them. Usually they exhibit hard starting even when cold (long whining of the starter before they ever crank up) and after they're hot and you shut them down, they "almost" start, but never do. The engine has a sound, like it's trying, but just can't quite seem to manage to kick over on it's own power without help from the starter. That's my cue that the valves need attention and I perform a leakdown test...or just pull the head if I'm in the mood.


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04-16-07, 08:39 PM   #30  
Azis
Posted By: Azis cheese,
I also have a kohler on a cadet that shows similar symptoms. However it will sometimes restart or at least try much sooner after it dies. I have looked at it a few times but not had it in my shop yet, but will this week. I can't remember all I have done with it but, I do recall getting to the point of blaming the fuel pump.

TIA
Appreciate your time and experience
I have this Cadet in my shop now and have ran it enough to duplicate the problem. It still seemed fuel related and I replaced the fuel pump. It did run longer, nearly an hour as opposed to 15 min the before. It will try to fire and sit and puff like it must have spark. Gave it a shot of fuel a couple times and it fired right up, acted like nothing happened, for only a few minutes then repeat and finally not restart till cooled off.
I checked fuel lines filters, sucked a few bugs outa the tank into the filter LOL one beetle made the trip in one piece.
All of this was only after heavy mowing wet grass, I nursed it back to the shop and checked for spark and had none. Let the test lead hang a min or so and then it was.
So now I still have to find an eliminate the kill circuit. I dont think I have had the shroud off of one of these.
Any heads up or dont do's

Eh its a CV12.5s

 
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04-16-07, 08:49 PM   #31  
It should be pretty simple...like a briggs...just a white kill wire going to the coil. By your description, I'd be leaning toward a bad coil (ignition module as Kohler calls it).


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04-18-07, 02:41 PM   #32  
Azis
The wiring might be like a briggs but the shroud aint lookin like no briggs I worked on.
This is a horizontal shaft, single on a Cub Cadet. It has a bellows around a drive line going the a simple firewall and then the hydrostatic rear drive.
I aint pulled nothin off but I just wandering if that shroud is solid round. Sure would hope not but I cant tell yet.

 
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04-19-07, 10:23 PM   #33  
You have me confused now....you said it's a CV12.5 which is a 12.5 horsepower vertical shaft kohler command engine. Run of the mill kohler command. If yours is a horizontal shaft, it still could be a simple system, but it depends on what setup you have. The K series had points in a box on the side of the engine, magnums had electronic ignition and some had automotive type ignition, and the commands have regular armature coils like most other engines. Some had spark advance modules.


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04-20-07, 06:02 AM   #34  
Azis
Well the numbers on the engines say CV12.5S, which is what I specified when I ordered the fuel pump, which fit and worked.
It looks like a vertical shaft but the engine is mounted horizontally with a pulley on the front (front of the mower at least, the shroud of the engine faces the operator) for a belt that goes down over two more pulleys back to the deck, and a drive line coming out the shroud.

I will take a few pics this morn and put em up, get back to ya with a link.

From what I can see the shroud is solid around the drive line. I am hoping I can just pull it back far enough to get to the coil without removing the whole thing.
I think it only has the coil, one white wire it looks like, and the voltage regulator mounts on the shroud.
I haven't tried looking for a manual for the cub yet, I will get those numbers as well see if that'll piece it together.

 
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04-20-07, 08:42 AM   #35  
Azis
Well I can't even blame this one on my peepers gettin bad, cuz I wrote it down correctly as, CH12.5S. Musta got lost in my memory dodgin all this cold n rain.
Sorry for the confusion.
The Cub #'s are
Mfg #134-214F100
Ser.# 241875
Model# 2135

Sure hopin it uses the same coil as the V doh, already ordered it, through Deere , they love me too

I put 3 pics up, including one of the driveline.

http://www.asis.phanfare.com/album/122717#imageID=15635803

 
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04-21-07, 12:29 AM   #36  
As far as I know, they take the same coil. Looks like you could unbolt the driveshaft and swing it out of the way to get the shroud off if necessary.


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04-21-07, 07:16 AM   #37  
Azis
I checked the coils and they do use the same one.
I will get it no worries, specially if I use the right manual LOL!
The high tension lead comes right out the top there so hopefully I can get to it just pulling the shroud back a bit. If not there are just two panel bolts holding that firewall, prolly slide the whole thing back bellows and all.

 
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04-27-07, 10:27 AM   #38  
Azis
Just to close out the second half of this thread,
I was able to remove the upper shroud bolts, as the lower most two were near impossible to get at without raising the engine due to proximity of the frame. Remove the battery and supports for the fire wall and make enough room to access the coil.
Replaced the coil and used the mower heavy duty, for about an hour. I feel confident that was the problem.

 
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04-28-07, 01:23 AM   #39  
Sounds like you got it! Thanks for the update. I guess it was tricky doing the coil without removing the shroud all the way!


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