Export thread

The following engine is one my Bolens’ 3012G (ST125) lawn tractor that’s in pretty good condition:
B&G Model: 404707-0117-01
12.5 HP
Air cooled

Issues:
1) Max RPM below standard?
2) Throttle lever pushed to max sinks to ¾ distance (drops ¼)

History:

Machine fairly well maintained; not abused. Bought new around 1987. Debris (dry grass and leaves) under front of engine – moistened with oil that dripped from common fills somehow caught fire. Engine stopped and fire (front of engine at bottom) was sprayed out with dry chemical extinguisher. After debris was removed and area brushed out _ perhaps not as gently as I should have – the machine started, ran and cut the lawn in normal fashion but then began to smoke and shut down. Unable to restart. I suspected some wires in the from may have melted and now are causing a short.

Replaced the magneto with one for a salvage yard. Though it didn’t start, the experience lead me to find a shortcut to threading the wires to the plugs so I reinstalled the orginal magneto thinking the few patches I made to a wire or two may have sealed the electrical “leak” where the shorting was occurring… if that were the case. The machine started, permitted me to mow about an 1/8 acre, then shut down again. Took the unit to a shop with high Angie’s List ratings and got it back with the follow $312.20 invoice:
#8051 B&G Ignition coil………….. $69.99
#592831 B&G stator………………… 99.99
1.5 hr Labor ……………………………. 112.50 ($75/hr)
Shop supplies………………………….. 9.99
Total………………………………………… $312.21

Comment & Questions:

If my machine has a magneto (which I KNOW it does)… why can’t I find “ignition coil” and “stator” on the parts diagram in my B&G repair manual? In short… does this engine actually have the two parts I was charged for?
Given the behavior of this machine AFTER the repair… what could possibly be wrong now? I assumed this shop had proper tools necessary to make the proper adjustments but I was the once who had to provide the RPM spec for the Governor idle. A tad unnerving. Very suspicion now.

The ignition coil would be the ignition module, that you were messing with by sealing the wires. The stator is the alternator, and is located under the flywheel, and your battery wouldn't charge without it.

>>The ignition coil would be the ignition module, that you were messing with by sealing the wires.<<

Do you mean this ignition module is the same as what the salvage yard told me was the magneto?

What would be causing that throttle lever to slide down a quarter from full throttle? The owner of the repair shop took pliers to the front of the machine and bent something a few times then asked me if the revved up sound was high enough. I ultimately said "yes" after a few seconds and more tinkering but .... man... how the heck would I know? He's supposed to have the tools. I told him what the specs were for idle but I had nothing for running.

Yes.
A magneto is just a magnet that runs past a coil.
2 parts magnet , in the flywheel & coil on the mower.
There used to be a set of points but back in the 50'a Atom Industries invented the Hall effect ignition trigger to replace the points.
For a few years they were sold like that.
Then some smarty pante realised you could embed the trigger in the coil, call it a module and charge 3 times the price.
Thus you now have a "module" that cost $ 50 to $ 100 when you used to have a coil $ 20 and points $ 5.

Thanks for the explanation. So.... it looks like I have no reason to suspect the replacement of those parts as being the cause of what that lever sliding back a quarter. That leave what other possible sources? Anyone have any ideas? Also, where can I find specs for this engine that apply to the components that most probably are involved here? the owner was able to put is hands on specs for the machine running at highest RPM given that governor (I have the governor idle specs but not those for full run)/

Top no load speed is 3600. Also the most frequent cause of the throttle backing off while running is the throttle control cable has lost its friction properties due to wear or somebody putting lube where it doesn't need to be, In some cases requires replacing the throttle cable or in the case of some MTD products just the throttle control box attached to the dash of the riding mower.

This was a machine built by to original Bolens folks I believe. But... since MTD now has the brand... would I be asking for a cable or cable box? (Bolens model 3012 G ... also called ST125.)

You may have the one piece throttle cable, control, So you would be asking for a throttle cable assembly. You need the actually throttle control that you push to control the engine speed.

OK. One piece throttle cable it is. However... is it possible the owner may have simply bent a linkage in the front of that engine a little too far... or the wrong one... and all he has to do is straighten it a bit? He went in there with a longnose pliers, did some twisting, used a screw driver next, then looked at me a few times and asked "How's that?". I finally answered based on what I THOUGHT sounded like my old machine. Made me very uncomfortable to have a mechanic ask ME what the specs should be on a machine I brought to him to fix.

Anyway... that guy and I are gonna' have a brief chat this morning. I appreciate the help.

Possibly playing with the governor spring adjustments.

jaygreg said:

OK. One piece throttle cable it is. However... is it possible the owner may have simply bent a linkage in the front of that engine a little too far... or the wrong one... and all he has to do is straighten it a bit? He went in there with a longnose pliers, did some twisting, used a screw driver next, then looked at me a few times and asked "How's that?". I finally answered based on what I THOUGHT sounded like my old machine. Made me very uncomfortable to have a mechanic ask ME what the specs should be on a machine I brought to him to fix.

Anyway... that guy and I are gonna' have a brief chat this morning. I appreciate the help.

Click to expand...

Any idea how many time I have set a machine to the specificed seting , taken it back and been told "it's wrong"
It never used to throw the grass that far before, or it used to throw the grass further etc etc etc.
gave up trying to explain that the mower had been slowly going out of tune for the last 10 years.
The customer liked or wanted it back the way it was, they are paying the freight so unless "like the way it was" is actually dangerious , "like the way it was " is it.
There is 5/8 of SFA difference to the way a mower works running at 3,600 rpm to 3,200 rpm
But 3200 will sound a lot quieter which makes the customer think the engine is running better.

as for yout fire.
A very very very common occurence when people neglect to clean the clippings from around the pulleys on the deck.
On a lot of decks the pulleys can run on the chassis which throws a few sparks or the friction of the belt running against the clippings gets high enough to start a fire.
Remember the trick of starting a fire by rubbing two sticks together surrounded by some shredded bark or grass.
Well that happens under your mower particualrly if you are cutting long dry grass very high.
Whites were notorious for doing it down here as there was a cut away in the chassis to give clearence to the clutch pulley and when the belt was old the pulley rubbed on the chassis throwing sparks into the fresh cut grass