OK You WD Gurus...

have you cked the rocker arm clearance?if you have a tight rocker it will do that when it gets up to temp.ck them all...

Maybe start by checking compression a couple different ways and check for leak down in each cylinder. Check for leaks around intake and carb.????

Edited by CTuckerNWIL - 16 Feb 2012 at 7:33pm

I did have the exhaust manifold planed and put on all new intake/exhaust gaskets. It's not a steady miss where you can pinpoint it to one cylinder. It is intermittent, but definately worse under load with engine good and warm. I thought about converting it to 12 volt just to see if that cures it, but I don't know if it's electrical, mechanical or fuel related. It is very annoying.

Yes, it got a new coil when it was refurbished.

I am going to go out on a limb here. but I am thinking that there is a wild chance that the timing is off by a tooth or 2 when it was reassembled. My reasoning is because it will start and run fine when cold correct? Assumeing it does, I am thinking that when it is getting good and warm the "skip" you are hearing or feeling is a combustion "PING" from the timing being off and the spark occuring at the wrong time. This would explain why you cant pinpoint the cylinder where it is happening, because it is probably doing it on all for at different times. I am thinking it isn't the timing where the magneto is bolted on, but more the timing gears in the front cover.

My dad would have me unscrew the sediment bulb body out of the buttom of the tank first. Hopefully it will be this simple. I have seen him do this more then once on old tractors he'll buy. They might have just enough gas to make them run, but not enough to make them run good.

Taking into account that this condition has existed over many years, and many different things changed and tried, and that it's been worked a fair bit over that timeframe, that with exception of a valve lash or assembly/lapping issue, the skip isn't related to anything you've changed, nor related to fuel quality.

I would not discount the magneto as being part of the problem, nor would I suggest that changing to a 12v electrical system would have any effect whatsoever, because of what Charlie noted above.  I also wouldn't predispose myself to assuming that since the mag is working, AND it was fully rebuilt a decade ago, that it's working properly.

In order for an engine to run smoothly, the ignition needs to be stable, consistent, and of sufficient energy to light the mixture.  Likewise, the fuel/air ratio needs to be stable and consistent.

What I WOULD do, is clear your mind of everything you know about the machine, and start over as if you know nothing. 

Warm it up, until you can make it 'skip'.  Then SHORT one plug wire at a time (Don't lift it, because that will cause it to discharge elsewhere, and risk damaging the magneto or creating carbon-tracking in the cap and housing).

By lifting one at a time, you'll get indication as to which (if any) CYLINDER is affected.  The engine's note SHOULD change with each one lifted.  If you lift one, and it DOESN'T change the engine note, that cylinder is not firing. 

Now... what you describe sounds like an intermittent miss.  IF you have one cylinder that is intermittent in firing, and you pull that wire, the intermittent miss will become a constant miss... it'll be smooth and rhythmic.

IF the miss follows one cylinder, trade the magneto wire and plug for a different cylinder, and try again.  If the miss follows the plug and wire, replace ALL plugs and wires, and when you do, make sure you're using solid-core wires and non-resistance plugs.  Magnetos don't operate properly with resistance wires and plugs.

If you find no change to the arrhythmia regardless of which cylinder, then what you're hearing either ISN'T a missing cylinder, OR it's a random miss of ALL cylinders.

A random miss could easily be the result of magneto problems- mag coil, condenser, or points.  Without a known-good-substitute, the possibility of proving the mag out is nonexistent... but looking to the other possibility would be a matter of altering fuel mixture to look for a change in performance.  With an intermittent miss present, pull the choke out a little bit, and see if the miss changes.  If it goes away, we have an improper mixture.  If it doesn't, it's still ignition related.

Mixture issues come in many flavors.  You described what appears to be load-related of a well-warmed engine.  I would suspect, by your description, that something that is getting WARM is changing it's characteristics, and one of the first things I'd check is the manifolds.  You said you planed the manifold, but there's more to it than the gasket interface.  I would warm it up good on a dark night, and put a load on it (PTO, or drive up a gravel country road with the hood off) and go looking for blue flashes of flame coming from places other than the top of the stack.  If this doesn't yield any clues, the next thing I'd do, is borrow an intake/exhaust assembly from a known good-running machine, and repeat the test.  Don't just change the manifold... change the carb and exhaust too.  IF this eliminates the problem, then your issue is either in the carburetor, or the manifold, or the exhaust.

One of the conditions I discovered that vexed me like yours, is a tiny crack in an INTAKE manifold runner of a (non-allis) industrial engine.  It exhibited a miss under high load and temp, and I eventually found that there was a tiny crack buried in that casting, that once warmed, engine expansion (block) and manifold expansion (heated carb base by contact with exhaust, like an Allis) would cause the crack to open up just enough to leak into THAT cylinder, causing a misfire.

Fuel/air mixtures that are in a very LEAN condition tend to become very difficult to ignite, hence a miss.  Many guys will 'throw parts' at an engine, oftentimes they'll solve problems like this by going to a 'racing/performance' ignition system, and since the miss goes away, they predispose themselves to thinking the stock system is inadequate, when in actuality, all they've done is masked the REAL problem, which is a tiny vacuum leak when warm. 

If the intermittant miss occurs on all cylinders, the issue is most likely to be found closer to the carburetor.  It also may be that you have a crack within the carbeurator somewhere, and under cold running conditions,

And this is when I return the valve lash/lapping issue.  A valve that isn't seating properly will make a cylinder draw fuel/air differently, and the result is a miss.  Checking valve lash is always a good idea, but I would not jump into pulling the head until I'd checked everything else above.  My gut feeling is that the problem hexing you is successful at doing so, because it's incredibly simple, and incredibly tiny.

My WD had about the same problem...changed out everything in the mag and it still skipped a little.Finally realized the wire going to the kill button on the mag was slightly shorting for some reason.The button did have a little rust on it but sure if that was causing it or not,but did remove the wire from the kill button and the skip stopped.Of coarse now to shut it off I have to shut the throttle off fast to kill it.When this mag goes out I plan on getting another one.

Terry GA wrote: My WD had about the same problem...changed out everything in the mag and it still skipped a little.Finally realized the wire going to the kill button on the mag was slightly shorting for some reason.The button did have a little rust on it but sure if that was causing it or not,but did remove the wire from the kill button and the skip stopped.Of coarse now to shut it off I have to shut the throttle off fast to kill it.When this mag goes out I plan on getting another one.

Autolite 295

I checked the owners manual and it calls for AC45 plugs. I looked at the tractor and it has AC R45 plugs in it, (R for resistor I assume). Is this my problem?

Found some Autolite 295's and put them in. I won't get to find out until spring if they help but she sure runs nice in the shed. Do you think this was the culprit?