Does the Cub Lo Boy use a wasted spark?

[sideburnz]

I'm sure this will be a very simple question for someone here. I guess what I really am trying to figure out is if cylinder #4 sparks once per engine revolution, or twice per engine revolution.

The short story is I've got a little induction tachometer on my Lo Boy 154, and I'm trying to decide whether it is displaying only half the actual rpms that the engine is doing. At full throttle it is showing about 1100 rpm, which is about half the maximum in the service manual as I understand it.

If the cub does use a wasted spark I guess I've got a much longer story to get into....

Thanks

[Eugene]

No.

[Greg Armstrong]

Does your tach have a setting for number of cylinders?... A 4 cylinder sparks 2x per revolution, and 8 cylinder sparks 4x per revolution. If it's setup for 8 cylinders, you're at 2200 rpm.

[MiCarl]

I have an inductive tach like this one:
.
It was giving me fits on my F Cub. The reading was inconsistent and I couldn't adjust the high idle above 1400. I've had problems with it on some motorcycles too.

I ended up setting it for "fires twice per revolution" and wrapping it around about 4" of the lead from the coil to the distributor. Fired up the tractor and it read 2100 rock solid. Turned the governor down to the 1800 it's supposed to be and am glad none of the engine insides came outside in the process.

I think there is noise in the Cub ignition system that gives my cheap induction tach fits.

[Landreo]

The spark plug fires once every other revolution. Normal 4 cycle stuff. If you have a "tinytach style" tachometer, it maybe expecting a wasted spark ignition that you would find on a Briggs, Honda, etc.. small engine. They will fire once every revolution although one spark is a wasted spark.

These were typically made for one cylinder engines and will pick up impulses from nearby plug wires and trigger excessively unless you have some shielding on the pickup wire.

[Larry B]

If you have a chainsaw see what the tach reads at full speed. Most saws will run somewhere around 10,000 to 12,500 RPM. If tach reads about that then double whatever it reads on the tractor. Like Landreo said you may get erratic readings on a multi cylinder engine. Most of the little inductive tachs are made for single cylinder engines.

[BigBill]

The camshaft has one revolution to the crankshaft one revolution. The distributor fire once on each cylinder during these two revolutions of the crankshaft.

You need a tach/dwell that switches between four, six and eight cylinders. I have all this older equipment. The funny part is I use it on my old willys

[sideburnz]

Thanks for all your insights. It's a little tach like the one pictured above. It has no settings. I'm pretty sure it's expecting a wasted spark, so I'll just keep that in mind and double what I see on the display.

Thanks again,
Matt

[Landreo]

If it is the same a MiCarl's tach then go here:

http://www.enmco.com/pdf/PT14-Engine-Monitor.pdf

The s1 button should set the tach to every other revolution.

[sideburnz]

If it is the same a MiCarl's tach then go here:

http://www.enmco.com/pdf/PT14-Engine-Monitor.pdf

The s1 button should set the tach to every other revolution.

It's a real cheap-o, no buttons to be found. I'll just do the math.

[outdoors4evr]

Also, make sure your pick up coil (where it is wrapped around the spark plug wire) is well separated from the other spark plug wires. There is a good amount of EMI (electromagnetic interference) emitted from the copper core spark plug wires. You are probably just picking up noise from one of the other plug wires.

[Landreo]

His problem is that he is not picking up enough impulses. He could try taking the impulse from 2 plug wires. Try wraping the induction wire around #3 and #4 spark plug wires which should trigger once each revolution which is what his tach is expecting.

[popeye2347]

No