I am still here but who knows for how long. I have been fighting an ancient computer for 6 weeks.

I saw your original post and since you were getting advice from one of the best Tech there is here, I did not interject myself.

I take it that the flywheel key was OK? Did you torque that flywheel to 150 ft. lbs when you re-installed it? Also, this engine should run quite happily on one cylinder, you say when you pull either spark plug wire it dies, not normal. Should start and run on either cylinder but have no power.

Might check your "Static Governor" setting. I could send you a manual but will be away from computer until Wednesday evening.

Walt Conner
wconner5 at frontier dot com

This post was edited by walt2002 on Tue, Aug 12, 14 at 8:27

I'd try a new coil.Do a test run w/o the kill lead plugged in first to eliminate a partial grounding as it runs up. Even though this coil throws the spark to both cylinders at the same time it doesn't mean that A) the CD is necessarily throwing the spark at the proper time consistently or B) that both wires are delivering the spark as it should.

Hi Guys,

I appreciate your responses & will do my best to define the problem & address your suggestions.

Sorry Walt, about your aging computer. I think you'd be happy with a new laptop, as I was after I canned my POS cpu, keyboard, mouse, etc.

Regarding flywheel, the key was like new, torqued as tight as I dare with breaker bar & the mag-to-wheel clearance was .010"+.
Yes, she will start, but when either plug is pulled, it dies.
The machine just won't rev up.
Static Governor? Prior to my problem, the governor was set fine; never hunting or sluggish.
In fact the machine was performing like new after hours of mowing & hauling brush in my trailer. Then suddenly it wouldn't run strong enough to move under its own power.

Are we (you) sure it's not the mech. compr. release?
I'm told it doesn't have one. It always started, but even with a new battery it would barely crank past the hard spots on compression strokes.

As for the coil, all was clean & no signs of abuse or abrasions. Tomplum suggests to unplug the kill lead.
Is that the line from the coil with the male/female connector at the front side of the engine? I'll try that next. Are you suggesting it could it be plug wires?

Interesting........I'm still listening if there are any other good doctors out there.

Thanks again,
Dave

Well, your 42A707 certainly DOES NOT have a mechanical compression release. The "compression release" feature on this Briggs engine is more a compression "lowering" camshaft design than an outright apparatus. The compression release on this engine is based on the principle that at low (cranking) RPM some of the air/fuel charge is bled back into the intake manifold because of a "high spot" made into the camshaft lobe base circle for the intake valves. At higher (running) RPM the high spot on the camshaft passes the valve tappet too quickly to permit an appreciable amount of compression to bleed back.
I am with tomplum on being suspicious of the magneto.
My opinion on what is happening is that because the mag actually fires a spark to both plugs at the same time, removing either plug wire increases the resistance (air gap) to such a degree that the coil cannot fire a spark at all.
On a "normally operating" magneto ignition on one of these Briggs opposed twins, removing a spark plug wire can be done to identify a non firing cylinder that may not be operating because of a problem in one of the cylinders (or a bad plug).
But, a magneto that has suddenly developed a problem causing it to only be able to make a weak spark might act the way yours is doing.
This ignition system configuration on the Briggs Opp Twins is call a "wasted spark". Because the 2 cylinders are on different strokes when the spark occurs (one cylinder is on a Power Stroke, the opposite cylinder is on an Exhaust Stroke) one spark plug fires and lights the air/fuel charge (power stroke cylinder) while the opposite plug fires a "wasted spark" on its cylinder's exhaust stroke.
The Briggs Magnetron magneto on these engines is designed with the intent that 2 spark plugs are being fired with each discharge of the magneto.
Having a magneto become weak could be the reason for your symptoms.

OK...I'm digesting all you've said. No Tums need yet.
The issue is probably not the "compression relief " feature.
It sounds as if that function occurs via fixed conditions, i.e., no mechanism, no adjustments,

The mag may be the culprit. After pulling the flywheel for inspection & reassembly days ago, I had both (new) plugs rigged & grounded to watch the electrodes. I gave it a crank & noted there was simultaneous sparking at both plugs. Thought this was unusual. Also, the sparks were a faint blue, and not audible. Normal?

My homework assignment now is to pull the kill lead to check for grounding, right tomplum? As you stated, "Do a test run w/o the kill lead plugged in first to eliminate a partial grounding as it runs up." Then check for good sparking.

If the magneto is bad, does that include the ring of coils below the flywheel AND the coil with integral plug wires?

As you may have surmised, I'm not real familiar with CDI ignition systems. This engine is the newest of my 20 some odd engines used here on the farm. Most are 50's & 60's vintage.

Thanks in advance again for your continued support,
Dave

The entire magneto assembly is what you see sitting beside the flywheel when the flywheel cover is removed, there are no other parts related to spark. The spark plug wires are considered part of this assembly.
The coils underneath the flywheel are the alternator stator coils, and are not in any way affiliated with the ignition system.
The spark magneto is completely self operating entity and generates its own electricity to do all the functions for spark generation and control.
The single wire that connects to the magneto is the "kill wire" and that wire is a grounding wire. The wire becomes grounded by the switch when the "ignition key switch" is turned off. Grounding that kill wire halts the electrical functions of the magneto and the engine dies.

Hey Mownie,

I'm on it!! I just opened the barn to check the suggestions you guys have made, but wanted to check this site for last minute inputs.

I will disconnect that grounding lead to eliminate any potential short there. Then turn over the engine with the plugs clamped to ground and report back with a description of sparking action. I'll then thread them in to see if I got lucky with something and hopefully she'll run.

Chat soon,
Dave

Hey All,

I turned the engine over via electric start with the grounding wire unplugged.

Both plugs were out & rigged together to ground.
Each plug sparked together in rhythm without missing a beat. The spark was small, a faint blue and stayed within the gap.

I put both plugs back and it started but stalled quickly.
Still sounded weak. On second try the battery wouldn't turn the machine over anymore. It's on overnight charge now with my motorcycle maintenance charger.

Only God knows what it could at this point.

I took the bike out this afternoon and stopped to look at a nicely done IH Cub Cadet 107 for $1200 with a 42" deck.
That would fix things!

Too stubborn and too hooked on fixing my what I have.
Just need someone to point at something I missed.

Keep in touch.....I hate giving up.
Thanks, Dave

Your spark test would have been conclusive had you not seen any spark , but not as it is for a number of reasons. I've seen these very same coil packs not run up well that had spark. I can't say for sure that your coil is bad or good as there are too many variables. Things do seem to point that way though...

Another misleading factor in the act of removing spark plugs from the cylinder and trying to observe spark quality out in the open is that the plugs ARE NOT under the influence of compression under those conditions.
Compression has a profound effect on whether or not a spark plug (or the rest of the ignition system) can/will throw an arc between the 2 electrodes.
Compression can stifle a spark from a weak magneto, but the same plug and magneto might still make a spark out in open air.
That entire phenomenon is why Briggs instructs ignition testing to be done using their spark tester.
The Briggs tester is an inline apparatus that connects in series between the spark plug and the spark plug cable and testing is done while the spark plug remains in the cylinder.
This not only accounts for the compression effect, it also forces the engine to CRANK at its normal RPM, instead of spinning faster (which affects spark too) as it would with plugs out.
A "poor boy" way of simulating the Briggs tester can be done by inserting the tool end of a VERY WELL INSULATED Phillips screwdriver into the spark plug cable and then position the metal shaft of the screwdriver about 1/4" away from the boot end of the spark plug. Best have a helper crank the engine while you concentrate on watching for a spark to happen.
If the magneto will make a spark capable of jumping the gap at about 1/4" spacing, it will fire the plug.
If not, then it is too weak for service.

The battery took a good charge overnight and I just got back in after doing the "Po' Boy's" spark test.

I pulled the left side plug wire and inserted a Phillips head into the female end where the plug goes . (left side wire stayed secured to its spark plug) then gave a crank.
I was able to hold the key on as the engine turned over while observing the spark jumping the gap between the screwdriver shank & the top of the plug.

From less than 1/16" I got continuous sparking without skipping. As I drew the screwdriver slowly away from the plug tip, the spark would stop arcing at 3/32", precisely.
I repeated the procedure several times to try and draw a longer arc but it consistently gave me only a 3/32" arc.

Did the same test, opposite hand, to the right side, and got exactly the same results. In both cases the spark was a light blue color and thin; about .005" or so in width.

After putting everything back together and again, it would start, run weak, falter then die.

Does the spark test appear to you guys as a bad coil?
I'm at the end of my rope, but don't want to kick the chair out yet.

Thanks all for staying with me on this one. Hopefully we can all learn something when I get this maching running again.

Sincerely,
Dave

OP - based on your last test results, coil is definitely marginal at best and needs replacing, imho.
When you first start engine, cyl head temps are relatively cool and compression is reduced. as engine quickly warms up, cyl head temps go up and compression increases, making it just that much more difficult for spark plugs to keep firing.... engine dies.

BTW, that spark you observed should have been a BRIGHT HOT blue @ 1/4' and - by all rights (as you are a novice) shoulda knocked you on yer keester when you were foolin with the phillips screwdriver... :)

Well, bad coil you say....probably so.
The plugs are new & all wiring looks proper.

No, I didn't get bit by contacting the phillips.
Done that before so I kept my hand on the plastic handle.

I'll see about a new coil next week when the shops are open. If I should be seeing a 1/4", bright blue spark, I'm not with this test. I let the battery hit full charge with the low amp charger on all day.
I'll try again tomorrow and see if the spark is any better.
Probably not.

Interesting to see if others feel the coil is junk.

Thanks for your input, rcbe.
Dave

This post was edited by Alberti on Sun, Aug 17, 14 at 5:41

This morning I called the local shops & found one guy who gave me my last tip. Run the engine and spray carb cleaner down the open throat of the carb. If it revs up, it's a fuel problem...I tried and it just killed it. Did it the same thing a few times.

So, I just brought it over to his shop for an instrument spark test and compression test.

We'll see. Just can't figure it out. He's an old timer (like me) and feels the spark is proper; coil is good.

More to come,
Dave

OP - dunno just who these tipsters are, but they ain't tipping you very good. Spraying carb cleaner or any similar combustible into the carb intake of a running engine is most likely going to flood/stall the engine.
My one time comments with the bark on: There have been at least 3 of the very best, most experienced advisors on this forum (not including me, I'm no expert) suggesting that your magneto is marginal. You seem to keep on debating that for various reasons.. get the magneto tested. Also, you have not answered if you did re-torque the flywheel to150 ft.lbs (and did you have all mating surfaces pristine clean before torquing) - just romping down on it with a breaker bar doesn't cut it.

so, fish or cut bait. I'm outta here.

I took the machine to a 45 year old mower shop.
For $35 they did a diagnostic to include an instrument compression test & spark test.

Spark test passed and so did compression test.
Still ran like crap. After pulling the heads the valves looked good but not the left side piston. It was sloppy.
The bore measures .060" over and egg shaped.
Just old & tired.

Bottom line; not worth reworking the cylinders & valves, then have the hydrostatic tranny go bad.

I realize this topic is done, but why would an egg shaped bore give good compression readings. It seems to me that good compression means the rings are still doing their job.

The way it was explained to me is that compression changes depending on when & how you test it.

I may have understood it wrong, but when tested while cranking without starting, the compression reads low due to the compression release feature. Don't know if it can be tested while running.

Then it was explained when the engine runs, compression is lost through the rings/wear on the cylinders. there is a static test done where the cylinders are pressurized and then the leak rate past the rings is measured.

Anyhow.....the best way, according to the seasoned mechanic I used, is to pull the heads (check valves) and measure the bore, check for slop in the piston & visually inspect the cylinder walls. That's when my engine failed.

Wish I could fix it, but not worth the effort & $ based on 18 year old machine just waiting to have something else go bad.

Thanks for your concern,
Dave