312-8 starts and dies under load...repeat...repeat..repeat

[wmsue 4]

Hi all,

 

New to the forum but not new to WH.

 

I've got a Charger 9 that runs great and I use to plow snow. It's run great since 1967 but shows its age. I haven't decided if I will leave the original patina or disassemble and make look like new. But that is another matter. My real concern is below.

 

I also have a 1987 312-8 (2112 K804) that I use to mow 2 acres. I had a problem at the end of last season that I haven't been able to figure out. Hopefully someone can stear me in the right direction.

Tractor starts easily and runs great around the yard when the PTO is not engaged (mowing). When I am mowing under full load and very bumpy yard, the engine dies after about 2 minutes. It restarts everytime easily and then dies again when mowing under load. Sometimes I can quickly turn the ignition key off and then back on again as the engine is dying and catch it in time to die all the way.  I changes the ignition module coil at the end of the season and it did NOT solve the problem. I also rebuilt the carb. Any ideas what may be wrong?  My next guess is the started solenoid. Maybe all the vibration is interupting the current flow and when I turn the key off and on, it resets the circuit? I hate to change parts when I'm not sure what the problem is. Anybody else ever have a similar problem?

I don't really have a way to put it under full load till I get a new deck and start mowing. I don't have a snow blade for this one.

 

p.s. I'm also looking for a used rear discharge deck 42" if anyone has any leads.

 

When the windchill get into positive numbers, I'l post some photos.

 

thanks in advance

 

Bill

Kinsman, Ohio

[Ed Kennell 35,822]

Check the two PTO safety switches for loose wires or corroded terminals.

[stevasaurus 22,231]

Welcome to Red Square.    I think Ed has it figured out. 

[gwest_ca-(File Mod) 10,503]

Your 312-8 has magneto ignition that is self powered. The lone ignition wire is simply grounded to shut the engine off. When the wire is not grounded the engine should run. The safety switch under the seat must be open for the engine to run when the pto is ON. Operator falls out of seat with the pto ON and the engine quits because the seat switch closes. Sometimes this seat switch is very close to closing and a bump is all it takes to close it and stop the engine.

 

When the pto is OFF the ignition switch should be the only thing that shuts the engine OFF.

If the ignition wire has bad insulation from wearing on a sharp edge the bared wire will also shut the ignition down because the sharp edge is a chassis ground.

 

The starter circuit has nothing to do with the ignition.

 

Make sure you do not allow any battery power into the ignition wire because that will burn up the ignition coil.

 

Here is a good wiring diagram that may help. Each circuit has it's own diagram.

 

Let us know what you find.

 

Garry 

[wmsue 4]

Thanks for the quick reply.

That makes total sense. I have to wait till tomorrow to download the wiring diagram because the forum says I looked at too many today.

 

I guessed solenoid because I had the fused wire that connects to the solenoid on the wrong side of the solenoid a while back. When I did this by accident, the ignition switch, head lights, dash lights.......nothing worked. But if I jumped the solenoid and had the key turned to the run position, the darn thing ran fine. If that wire was on the output of the solenoid.....it might make sense. Lookin' at things backwards again.

 

Thanks and I'll give that a look.

Edited January 7, 2015 by wmsue

[953 nut 51,762]

    I think Garry has you covered on this!    

[Geno 1,928]

Let us know what you find and

[wmsue 4]

Short update.

 

I looked over the seat switch and cleaned up the connections. It looked good, switch made solid noise when contact was made etc. Now it's even cleaner and better looking.

I haven't torn into the PTO switch area yet. Just too darn cold the last few days. Will look today.

 

I do remember when I was having trouble that simply turning on and off the blade PTO would NOT change the fact that the tractor dies after full load of a minute or so. But if I turned the key on and off quickly (after the PTO was turned off) I could stop the shutting down. Can't figure that one out in my head.

 

I want to remove the PTO switch and do a thorough check of it today.

 

thanks for the wiring diagram and help.

 

Bill

[wmsue 4]

update again on the problem. It's Back !

Cleaned all the contacts and the entire electrical area back in January. Tractor has run great hauling things around the yard and mowing the grass once this season. It never skipped a beat......Till today !
The old problem is back. Here's what I noticed today:
1. I mowed for over an hour in second gear and full throttle before the problem reoccurred.
2. Got new gas today and filled up the tank before I started, so I don't think it's a fuel problem.
3. After mowing for over an hour it backfired, started to die but I could recover from it by turning off the PTO and turning the key switch off and on. This happened about 5 times. But what has me stumped is when I was driving down the lane without the PTO engaged the backfiring and dying problem happened again. Turning on and off the key, the engine regains speed and power. No backfiring under normal load. I assume the backfiring is from the excess fuel left in the cylinder when the ignition dies. I just downloaded and printed the wiring diagrams from Garry again and will dive into fixing it next week. Any suggestions where to start? I'd like to diagnose the problem and solve it instead of just changing parts. Since the problem only occurs under load and after an hour or so it's a bit difficult to reproduce. I did replace the magneto coil last year when the problem started. There is NO spark to the plug when the problem happens till I turn the key off and on.

thanks in advance for the help.

Bill
Kinsman, Ohio

[N3PUY 1,031]

Well, sounds like you have already diagnosed the problem as the ignition switch.   You didn't say if it backfires out the exhaust or back through the air cleaner.  
  I'ld bet it backfires out the exhaust!    An electricial problem will show up at the exhaust.  If it were a lack of fuel it would backfire thru the air cleaner.  AND a safty switch, like a seat switch, will cause a exhaust backfire.  Maybe when you reach for the key you are repositioning yourself on the seat?  Mine backfires when I slide too far on the seat when on a slope.
  Keep us updated!

[ericj 1,576]

i had a 312-A that use to do that also or something very similar but only when the tractor got hot so the hotter out it was the faster it happened. i swapped out the magneto  but did not help. finally talked to my dad's old dealer and he told me it was the valve sticking. so i took the tractor to him and he pulled the valves and sure enough it had carbon build up on it and the in the valve guide so he opened up the valve guides and did a valve job and sure enough it cured my problems with the tractor. he said that he had valves so tight he has had to cut the head off and then drive the stem down and cut it off till he got it all out. so from what he told me it will only get worse if you leave it alone and do nothing. good luck but i would look at the valves



eric j