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Willy

Mulie Motor

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Willy
My nephew called for some info on a B/S 15.5 hp motor. he said it would run for about 15 min then quit,when it cooled off it would start right up and run for another 15 min. I haven't seen it as yet,but I figured probably the condenser. I haven't had much to do with the vertical shaft motors. He had the sheet metal off and said the mice hadn't been at it. Any suggestions??? Thank Jim

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HubbardRA
A friend of mine had a 10 hp riding mower that did the same. When I checked it over, there was no clearance in the exhaust valve. After about 15 minutes of running the valve stem would expand enough for the valve to totally stop seating and thus lose the compression. I just lifted it up, put a file between the valve stem and follower, and filed the correct clearance. It ran great and did not stop after that. So I'd say to pop the cover and check the valve clearance. I have fixed two machines with this problem. Next thing I would check is gas flow. It has to be flowing faster than what is used when mowing or the carb will eventually run dry. It could also be a coil that opens up when it gets hot and closes back together when it cools. I have seen this a couple times also.

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PatRarick
If it's a 15.5 horse Briggs vertical shaft engine, it has Magnetron electronic ignition so there's no condenser. It should also be an overhead valve engine so the valve clearance is adjustable at the rocker arms. The ignition armature (coil) is the most likely suspect. First is to determine spark or fuel problems. As soon as the engine dies and fails to restart, check for spark. Next, unplug the ignition kill wire from the tractor's harness. It's a single wire that should be coming through a grommet on the tin shrouding around the cylinder. I can't recall for sure which side of the engine, but I believe it's the carb side. Checking with the wire unplugged will isolate the ignition from the tractor and verify that the problem is not with the tractor wiring, ignition, or safety switches. Check the ignition ground wire all the way to the armature to see that there's no bare spots worn through the insulation. I've seen where as the engine warms up, the wire becomes more flexible and expands to where it will lay on the block and finally erode the insulation off, thus grounding out the ignition. As it cools, the wire contracts and will move sufficiently away from the bad spot to where the ignition is no longer grounded. The next step would be to replace the armature. If you find spark when it dies and fails to restart, pull the fuel line off at the carb and check for fuel flow. Little to no flow, remove the tank cap and check again. If the tractor has a fuel pump, you may have to crank the engine to operate the pump and check the flow. If it flows after removing the cap, replace the cap. If not, unplug the line just behind the fuel filter and check for fuel flow. Low or no flow would be debris in the fuel tank or a bad fuel pump. Normal flow would indicate a bad fuel filter. If you have good flow at the carb when you remove the line at the carb, check the anti afterfire solenoid on the bottom of the carb. Like the ignition armature, they can go bad, heat and the windings can open, causing the solenoid to shut off the fuel at the main jet. If everything checks out good as to spark and fuel flow, remove the valve cover and check the valve clearance. As I said, the armature is the most likely suspect. Keep in mind that the Magnetron armature should have a lifetime warranty so you shouldn't have to pay for a new one. You will have to return your old armature for Briggs to inspect, however.

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andrewk
Magnetron ignition modules DO NOT have a "lifetime warranty" on them. It is merely a solid state module, fully capable of becoming faulty. In nearly 7 years in this business, I have replaced about 400 of these, and maybe 3 were warranty, because it fell under the warranty period of the engine. If you go to your local dealer and ask for a warranty on that coil, they will probably laugh at you, just so you know. I will look it up in the warranty policy and procedure book at the shop, but I am dead certain there is no warranty on that other than under the normal warranty period, which is normally 2 years for a homeowner application. ADDED- Just looked this up on briggs' site- seems like it only applies to the big block Vanguard, after researching on briggs site- it is only on some select commercial engines, and most likely the 15.5 you are dealing with is an INTEK, and not covered by this 'warranty'. Stemming from this- The test procedure laid out is what you should do to verify if the coil is at fault. There is a common misconception of the condition of either the legs or the trigger magnet on the flywheel- they can be rusted, and it will have no effect on the magnetic lines of flux that trigger the ignition. You might check the air gap, in case someone has messed with it, but by your description, the coil is intermittent. It could very well be vapor lock, or a bad fuel pump, if so equipped. Try pinching the line when the engine is running, and see if it makes a difference. No difference will tell you you have a bad pump, or at least a weak one. Vapor lock should go away right after you crack the tank, so that would be a nice easy test too. Back to spark, I have also seen where the high tension leads get a melt spot on them, and they ground the ignition too. Check both the kill wire and the plug wire- It should be easy to figure it out- I am sure you will figure it out quickly- Hope this helps, Andrew

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Al
Hi, For ANY warranty on these assemblies, they will be recalled by Briggs and the failure analyzed. Briggs has checked 100s of these units and the cause of failure is for all but VERY small percentage caused by 12 volts getting on the kill line. They do not warranty this. They also have a service bulletin out from about 20 years ago that specifically says that if you have a failure on a magnatron to connect a voltmeter, (not digital) (a test light will also work) to the kill wire to the module and switch from off to start a minimum of 25 times. This is to ascertain that no voltage is getting on the kill line even for a minute instant. This is instant death to these units. It comes from wear in the switches and and then a little sliver or a bunch of powdered contact get in the grease on the rotor and then occasionally makes a path to the kill line when in start mode. Instant death and can often not be repeatable. The reason not to use a digital voltmeter is that the sample time is too long and with a regular analog meter you only see a tiny flick of the meter. A digital meter would miss this and a light might not even completely light. Do I believe all of this? Quite a bit, but I think it gives them a method to reject warranty claims. 2 things. They could for pennies put a diode in the module from the kill terminal and this would keep a voltage spike from damaging the module. The other issue is that all of the other major engine companies have their share of failure of electronic modules and many have been casued by things like the substrate or the traces on the circuit boards inside cracking from thermal cyclilng and being intermittant. Can't believe mother Brigg"s milk is so pure that if never sours, as other companies has. Who is to challange them on this warranty issue. Kohler has their share in the past and there is a date code list. Any body that has sold Lawn Boy as I have for over 25 years can't count the module failures we have seen. Every time Lawn Boy gets a new vendor, we go through another series of module failures. Takes about 5 years to get through it. The first year to get in the field, the next to get enough failures to establish a problem, the next to get a fixed module and about 2 or 3 more years to get the units in the field purged. Al Eden

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