Whose switch logic is in Top form this evening?

[JohnRoberts]

Any updates? 
------
I swapped out the magneto on mine and am still seeing balky restarting when hot.

Just this morning I measured 4 meg ohms  to ground on one safety switch, and 25 meg ohms to ground on the main on/off switch. Of course they should be completely open circuits. The on/off switch is only a couple K ohms when closed (should be a short), but it is easier to stop the motor than start it.

I am not looking forward to replacing the entire wiring harness but that may be required if this is the reason for balky restarting issues when hot. I guess i need to test the safety switches themselves for leakage paths, wire shouldn't just go bad.

JR

 

[lassoharp]

I got a new PTO switch and harness assembly and just replaced everything I could.  That cured the intermittent connection and it starts just fine now.  Evidently someone had either tried to fix the connection problem with aux wiring or they were attempting to bypass safety switches.  After I got the mower started I just let it be. (relief!)

Those no-hot start issue seem to be common.  My previous mower would not hot start and usually took about 45 min-1hr or more to cool down enough for easy restart.

The usual suspects as I recall were no spark and loosening the gas cap.  Gas cap never worked for me and I had no spark tester.  I did try replacing plug and cleaning plug cap but it didn't help.  Sounds like you have the coil ruled out.  Any way to check for spark?

 

[JohnRoberts]

Good to hear of your success...  ;D
-----
I have narrowed my testing down a little more.  With the safety switches disconnected, it restarts even when hot as a fire cracker no problem, so I think I am on the right trail with the safety switches and wiring harness.

If I unplug the brake/clutch switches, the wiring shows full open circuit (good).  I removed tested and cleaned the brake/clutch switch and it seems OK, so my suspicion now is the seat safety switch and associated wires.  I am guessing a NC pole in the clutch switch opens up to defeat the seat switch for starting, explaining the high impedance when I unplug that switch, so my remaining suspects are the wire in the harness between brake switch and seat switch, and the seat switch itself.

Like Sherlock Holmes with his deductive reasoning, when I have figured out everything it isn't, what remains is what it is...  8)

This is not very linear troubleshooting, since these megohm leakages are hanging off a couple ohm magneto winding, so not very obvious, and the mower runs when hot, so not enough to kill it, just enough to make it not want to start, sometimes. Since I lectured you guys about not defeating the safety switches, I need to walk my own talk.... Ignoring that i cut my lawn today w/o full safety.

JR

   

 

[JohnRoberts]

Finally nailed it... after much dicking around, I removed the wiring harness to clean it and remove the extra wires and spare parts. Since I have a manual start mover I only need about 3 or 4 wires.  After I pulled out the harness I found a new surprise, the harness leading to the brake/clutch switch was seriously scraped up. it looks like it was being hit by the blade drive belt, while the steel cable for the brake/clutch mechanism runs right by it too.

One wire in the harness was cut completely through, but it wasn't doing anything so no loss... however the wire hanging off the magneto kill terminal had insulation scraped off so it was exposed to the elements. like wet grass or whatever is flying around down there.

I found another safety switch on the blade lever handle, but it was not connected to anything.

So my fault vectors for leaky impedance to ground giving me weak spark were multiple.  Surprisingly the scraped up harness wires wasn't the worst... Since the harness was universal, for the electric start mowers too, there was what looks like a programming dongle, with a 4 lead PCB with two pins connecting two wires to each other and leaving two others open circuit. Even though it was all inside a sealed connector It was showing significant leakage resistance to the other pins.

The on/off switch was pretty good, only 25M leakage resistance when it was supposed to be open circuit, but since I was fixing stuff, I pulled it out and cleaned it. I used a simple scrub brush to remove loose dirt, and got it to read open circuit.

I removed all the spare parts, several extra wires, and the whole programming dongle. Taped up the scraped magneto wire and reassembled the harness (I added some tubing around the harness JIC) . I used two cable ties and changed where the cable ties were attached to hopefully make sure the harness now stays  clear of the drive belt.  All the safety switches work perfectly and it now starts like a champ..

I'm not sure what the safety switch on the blade does, it is closed when the blade is engaged, so perhaps shorts the magneto kill  so you can't start with the blade engaged. perhaps that's a concern with electric start mowers, for hand crank you can't hold the blade engaged and pull the start rope at the same time so redundant.

I could have just disconnected the whole safety switch harness and mowed my yard (like i did last weekend) , but since I talked the talk about safety, I needed to walk the walk.

JR

 

[PRR]

> can't start with the blade engaged. perhaps that's a concern with electric start mowers

It is. Without interlocks, I can stand on the ground with my toe under the deck, blade clutch engaged, brake/shift in any position, and start the engine. Even the starter-motor would trim my toes. When warm the engine will catch and rev real-quick, shred my toes.

But WTH. Today I was rolling 200-pound boulders down into the ditch I was standing in. If I get my toes really flat, the mower blade will pass right over them.

 

[emrr]

Yeah, pick your battles!  : )

 

[JohnRoberts]

> can't start with the blade engaged. perhaps that's a concern with electric start mowers

It is. Without interlocks, I can stand on the ground with my toe under the deck, blade clutch engaged, brake/shift in any position, and start the engine. Even the starter-motor would trim my toes. When warm the engine will catch and rev real-quick, shred my toes.

But WTH. Today I was rolling 200-pound boulders down into the ditch I was standing in. If I get my toes really flat, the mower blade will pass right over them.

With my mower, the blade engage lever requires my feet to be holding down a pedal to lock it engaged, so the blade can not be held engaged without at least one foot on the lock pedal. This is hard to do if not sitting in the seat, so a mechanical safety system that keeps feet away from an operating blade. 

I can imagine someone with an electric start mower trying to restart after a stall, while sitting down with the blade held engaged. In my experience for the motor to stall, the blade is probably jammed by a tree limb or something wedged in there, so prudent to not re-start that way .

====
Yes life can be dangerous, but so often it is the routine stuff we take for granted that reaches out to spank us. I was impressed by the statistic about electrocutions, where so many technicians and engineers are the ones being killed. While they are also more exposed to higher voltages than most, we have all known the guy who was way too casual with mains electricity.

What are the rednecks famous last words? "Hey watch this". 

JR

PS: Look out for them rocks, first your toenail turns black, then it falls off as a new one grows out underneath it.  ugh.

 

[JohnRoberts]

Well my balky starting when hot has returned. I have been able to localize the problem to the Brake/clutch safety switch, which disconnects the seat safety switch for starting. With my VOM, I read off scale open circuit, even when hot, so to the best of my measurement capability, this safety switch defeat is working correctly, but the reality is, with this safety switch wire disconnected, it starts fine when hot, when switch wire harness is connected it is hard to restart when hot.

I have isolated the problem to this wire/switch, while measurements do not confirm an obvious fault. To fix this right I probably need to replace both the wiring harness and the brake/clutch switch. Arghhhhhh Leakage resistance is higher than tens of Megohms, but apparently still enough to affect the spark. 

I am thinking of wiring the seat switch in series with the key on/off switch, so i can defeat the seat switch for starting, then turn it on after I'm started and sitting in the seat. That way at least i get the seat safety switch function back, but lose the ability to kill with the on/off key switch while sitting down. 

JR

 

[lassoharp]

To fix this right I probably need to replace both the wiring harness and the brake/clutch switch. 

That's exactly what I wound up doing with mine(except was deck switch) and it seems to have fixed the issue.  Have you been able to take multiple sets of the same measurements, while working the brake with your foot in between so as to ferret out an intermittent?  The first set of resistance readings I did said one thing and later I happened to try another set and caught it doing something different.  As I sat and raised and lowered the deck repeatedly I noticed it was making circuit go open/close from the mechanical movements

I read off scale open circuit, even when hot, so to the best of my measurement capability, this safety switch defeat is working correctly, but the reality is, with this safety switch wire disconnected, it starts fine when hot, when switch wire harness is connected it is hard to restart when hot.

If I'm interpreting this correctly - the brake switch looks correct (Open) when hot or cold, but is apparently failing to (Open or Close?) the seat switch only when hot?  So with entire switch removed it's now impossible to make the seat switch prevent starting?

Have you checked the seat switch and it's ground connections for any potential faults?

That way at least i get the seat safety switch function back, but lose the ability to kill with the on/off key switch while sitting down. 

 

So raise up off the seat to turn off?  Seems safe as long as other ones are still intact.

 

[JohnRoberts]

I read off scale open circuit, even when hot, so to the best of my measurement capability, this safety switch defeat is working correctly, but the reality is, with this safety switch wire disconnected, it starts fine when hot, when switch wire harness is connected it is hard to restart when hot.

If I'm interpreting this correctly - the brake switch looks correct (Open) when hot or cold, but is apparently failing to (Open or Close?) the seat switch only when hot?  So with entire switch removed it's now impossible to make the seat switch prevent starting?

Have you checked the seat switch and it's ground connections for any potential faults?

Sorry I wasn't clear...  The wire from the seat switch is open circuited by the brake/clutch switch.  So the seat switch is trying to short out the magneto, but prevented by the break/clutch switch.  So seat switch can not cause the problem.

My problem is I can not measure a fault...  after many tries, since I reworked the wire harness it reads off scale open circuit.

I only determined empirically by disconnecting the wire to the brake/clutch switch, that it starts correctly hot and cold. 

That way at least i get the seat safety switch function back, but lose the ability to kill with the on/off key switch while sitting down. 

 

So raise up off the seat to turn off?  Seems safe as long as other ones are still intact.

Yup, or just use the on/off switch and try to not fall off it...  I need to see how much a wire harness cost for exactly 3 working wires. Arghhh

JR

 

[lassoharp]

I need to see how much a wire harness cost for exactly 3 working wires. Arghhh

I found mine at a lawnmower junkyard.  That can be an "Arghhh" experience if the guy who runs it is too much of an old codger wheeler dealer type.  The one here sort of was but seemed to have no interest in gouging on the wire harness and switch.  Headlights and bumpers and seats were a different story.  I was sideline shopping for a more comfortable seat.  I opted for an old chair cushion from the garage . . .

 

[JohnRoberts]

I need to see how much a wire harness cost for exactly 3 working wires. Arghhh

I found mine at a lawnmower junkyard.  That can be an "Arghhh" experience if the guy who runs it is too much of an old codger wheeler dealer type.  The one here sort of was but seemed to have no interest in gouging on the wire harness and switch.  Headlights and bumpers and seats were a different story.  I was sideline shopping for a more comfortable seat.  I opted for an old chair cushion from the garage . . .

The stock wiring harness has lots of spare wires for the electric start and stuff I don't need. There was even a plug in jumper PCB to connect wires to wires. I found dirt in these connectors that was exhibiting measurable resistance to ground.

I need only 3 wires in the harness: Ground to brake/clutch switch, brake/clutch switch to seat switch, seat switch to magneto. I can make my own wiring harness, but i repeat, I do not see or measure any electrical fault.  A fourth wire from the on/off switch connects straight to the magneto.

I remain suspicious of the brake/clutch switch mechanism, a cable actuated brake/clutch, with a limit switch. Perhaps I could replace the limit switch, while it measures OK when off the unit (on it too).

There is definitely a ghost in the machine, or at least in the brake/clutch switch assembly.  I have isolated it to this. Maybe I need to call ghostbusters?

JR

 

[lassoharp]

There is definitely a ghost in the machine, or at least in the brake/clutch switch assembly.  I have isolated it to this. Maybe I need to call ghostbusters?

That's what mine felt like for a while but it sounds like yours is showing no obvious circuit fault, which mine eventually showed with consistency.  I'm puzzled as to why you get instant hot start by removing the assembly.  I'd probably say good news there since it seems to rule out other common hot start issues that give people a lot of trouble, and points to electrical.

a plug in jumper PCB

Have you been able to check for broken solder joints?  Seems it would take a lot of abuse on lawnmower.  The main relay PCB in my Honda Accord would expand when left in sun with windows up and the cracked joints would go open with the expansion leading to no start - and actually a kind of "no hot start" since it was directly heat related.

 

[JohnRoberts]

Not much solder to go bad...  really simple circuit... kill winding on magneto that gets shorted to ground to kill the spark, open circuit to run.  I have a wire going from that kill terminal to the brake/clutch switch, that open circuit to it to allow it to start. 

I measure off scale high impedance with my VOM... still works better with that wire disconnected.

JR

 

[JohnRoberts]

I am starting to believe it's Gremlins not ghosts in my machine.

Today I added another switch to the wiring in series with the safety switches, so I could switch them out if I have trouble restarting when hot.

Just like watching a pot waiting for it to boil, it worked perfectly today with the safety switches connected in circuit.

JR

 

[JohnRoberts]

OK, another year later I am seeing a pattern to my ghost haunting my mower...and making it hard to start. 

it appears my ON/OFF switch, that should be an open circuit when on and shorted when off, is slightly conductive when it is supposed to be fully open. I have noticed several weeks in a row, that I can smell raw gas while trying to start the mower (presumably a symptom of no spark), but if I switch the ON/OFF switch OFF then back ON again, the mower starts the very next pull...  I normally leave the ON switch on and just kill the motor with the seat safety switch when I finish mowing, so apparently from sitting switched ON, weeks at a time this switch builds up a conductive path inside. 

Looks like i should replace the switch,,, I recall measuring a high impedance leakage last year, that went away after I cleaned it. I decided to take the switch off and measure it again today, but when I tried to unscrew the lead attached to it, the switch fell completely apart... Oh boy..

So now I got to really look at it's insides. I put some penetrating oil on the lead screw to get it off, so I could take the parts inside. Now  the condition of the switch contacts being covered in penetrating oil was no longer the same as when it was making it's mischief but I took the parts into my bench and checked them out. Even after cleaning everything with alcohol I was still measuring 20-30 MegOhm between just the two switch contacts sitting on a piece of bakelite. I am pretty sure bakelite is not a conductor so there must be a surface buildup with dirt attached to the surface of the bakelite creating a conductive path.

I scraped the top and bottom layer of the bakelite around the switch contacts until I got an open circuit measurement with my ratshack VOM. I cleaned the sundry parts and reassembled the switch. The bakelite wafer with the switch contacts on it is a press fit into the switch body, so I pressed it back in (with a hammer). I reinstalled it and the mower now starts (and stops) properly, but the real test is for the rest of the summer. I sealed up the back of the switch with tape, so that should keep new dirt and dust from accumulating inside. 

It will be nice to finally exorcise this ghost. My sense is that it doesn't take a very low impedance across the kill winding of a magneto to suppress the spark at slow hand cranking speed. Maybe this is finally fixed (again). 

JR

 

[lassoharp]

Very interesting find.  So layer of dirt and dust being the spoiler.  Wonder if that's a general phenomenon or possibly due to specific contents in the dirt layer?  organic matter vs metal particles or other semi conductive matter.  At least you were able to restore the switch.  I'd have probably bought a new one when it fell apart like that.

 

[JohnRoberts]

Very interesting find.  So layer of dirt and dust being the spoiler.  Wonder if that's a general phenomenon or possibly due to specific contents in the dirt layer?  organic matter vs metal particles or other semi conductive matter.  At least you were able to restore the switch.  I'd have probably bought a new one when it fell apart like that.

Yes, I probably should buy a new switch still..  ;D

Not sure what exactly is going on. I detected the high impedance path last year while trouble shooting but didn't think much of it since it went away after I cleaned (and apparently exercised the switch). I suspect there is iron in my dirt, so that and moisture could conduct. While I don't expect much voltage, there should be an AC voltage present at the magneto shorting terminal when open and engine is running, I don't know if that could organize the conductive dirt. Being AC I would not expect that it would.

I didn't plan to take it apart, but after it fell apart i looked at it , and I was able to re-assemble it. Apparently the bakelite is a press fit and gives a little, but there is enough slop in the design that it appears pretty robust now.

I don't feel good about the stock design staying clean, but after I taped up the air gaps where the bakelite sits in the switch casing, I am more optimistic.

We'll see.

JR

 

[JohnRoberts]

Well almost a year later I finally got tired of the balky starting with my lawnmower.  Last weekend it was a real PIA. It would run OK but was really hard to start randomly OK or not.  Last summer I took the ignition switch apart and cleaned it and taped it up to seal it. But I was measuring a few tens of Megohms across it this week, when open. So I replaced the ignition switch with a new one. Cost about $4**.  Best $4 I spent.  Started on the first pull today.  ;D ;D ;D

It is hard to imagine that 39M shunt across the kill winding would make it hard to start, but empirical evidence suggests that sometimes a new ignition switch is the right call.  8)

JR

** that is $4 plus shipping and handling... so more than $4 but still good.

 

[lassoharp]

It is hard to imagine that 39M shunt across the kill winding would make it hard to start, but empirical evidence suggests that sometimes a new ignition switch is the right call.  8)

Agreed.  I probably would have counted it open and good.  Interesting that it does cause issues.

Great price on the switch too.  Think I paid about 15$ for mine.  At least the aggravation is gone now.  Happy mowing!