Fires but no start

[Clark Thompson]

make sure your rotor button is timed corectly. Install mag with # 1 piston top dead center on compression stroke. Make sure that the rotor is pointing to number 1 on the distributer cap. Hint !! you wont be able to install the mag so as to the rotor points directly to number 1. it will be just after number one. between number 1 and 3. after mag is installed rotate the engine backwords 1/2 turn. then the impules will be in time with #1 on the cap. This is assuming you didnt have the governor off the engine and the engine ran before.

[Clip]

As I have it timed now, the rotor points to #1, probably one or two degrees towards #3. Governor hasn't been adjusted at all since engine ran maybe 15 years ago. Like everyone says, "ran when I parked it."

When I pulled the mag off initially, the rotor was probably at 30-40 degrees clockwise from #1 and I wasn't getting any spark. Thought this was kind of interesting as I don't think it was messed with since it ran, but I matched the rotor and pinion marks to get spark back.

[staninlowerAL]

As I have it timed now, the rotor points to #1, probably one or two degrees towards #3. Governor hasn't been adjusted at all since engine ran maybe 15 years ago. Like everyone says, "ran when I parked it."

When I pulled the mag off initially, the rotor was probably at 30-40 degrees clockwise from #1 and I wasn't getting any spark. Thought this was kind of interesting as I don't think it was messed with since it ran, but I matched the rotor and pinion marks to get spark back.

I saw in an earlier post that you had checked compression but if the engine has not run in the last 15 years, I would look at the valves, might be sticking or other issues. Once you are confident that the timing is correct and you have spark at the plugs, you might try pull start it with a pony tank for fuel if you don't have the regular fuel tank in place. Just my 2 cents worth.

[ricky racer]

As I have it timed now, the rotor points to #1, probably one or two degrees towards #3. Governor hasn't been adjusted at all since engine ran maybe 15 years ago. Like everyone says, "ran when I parked it."

When I pulled the mag off initially, the rotor was probably at 30-40 degrees clockwise from #1 and I wasn't getting any spark. Thought this was kind of interesting as I don't think it was messed with since it ran, but I matched the rotor and pinion marks to get spark back.

I saw in an earlier post that you had checked compression but if the engine has not run in the last 15 years, I would look at the valves, might be sticking or other issues. Once you are confident that the timing is correct and you have spark at the plugs, you might try pull start it with a pony tank for fuel if you don't have the regular fuel tank in place. Just my 2 cents worth.

Good point, Stan regarding the valves. Another thing, I don't want to start a debste here but my experience with Champion plugs is such that I won't buy them anymore. I've spent many hours chasing ignition problems that turned out being the new Champion plugs I installed.

[Clip]

I'm pretty sure I've got it timed correctly after attempting to set it 180 out with poor results. Will pull the valve cover off and verify free movement of the valves and try the pony tank. I'm tossing around the idea of new plug wires. I was surprised to see all four ground electrodes were wildly different lengths, but gapped all to .023 and they sparked with no issue out of the cylinders. I'm used to running NGK copper with excellent results and Autolites in my domestics, might have to try a set in the Cub if they have better QC.

[Rick Spivey]

Clip,

Sounds like you have exhausted the magneto timing suggestions. Just for clarity, when I say 180 out, I am referring to the rotation of the rotor; so, instead of firing at the #1 tower when #1 is on compression stroke, it would be firing at the #4 tower. Remember, the magneto only turns once for every TWO rotations of the engine, since it only fires on the compression strokes, and not the exhaust. It now sounds like you had it timed right to begin with, so your problem may truly be fuel related. If yes, some starting fluid ought to get you a good spurt of activity, shoot it straight down the carb intake (take intake hose loose). Also, after a prolonged period of inactivity, some cubs will only crank when pull started, the first time. After running a bit, they normally settle out and start more easily. It probably has to do with piston rings a bit stuck, and/or valves not fully seating. Once you get it running, try a little Seafoam through it, that helps clear up deposits and stuck "stuff".

[Clip]

Thanks for clarification on the 180 out, Rick. In that case, I've tried it 90 out and 180 out then watching it fire with open valves. I'll get the shifter welded up, adjust clutch free play and might tow it around the yard a little after I make a pony tank for it.

[staninlowerAL]

Thanks for clarification on the 180 out, Rick. In that case, I've tried it 90 out and 180 out then watching it fire with open valves. I'll get the shifter welded up, adjust clutch free play and might tow it around the yard a little after I make a pony tank for it.

This is where I started with one, it sat for 30+ years without the engine being turned. Had to pull start it the first time.

[Clip]

Quick update: tried checking for spark using a handheld spark tester (the kind you hold on the wire and watch for a bulb to light up in the handle), and also used the timing light's pickup to check. The handheld tester wouldn't indicate spark unless I was holding it on the coil wire, and gave a very dim, intermittent flash. The timing light would indicate the same when I had the pickup on the four spark plug wires, seemed like wire 4 flashed a little more than 1 but all were intermittent.

These results don't agree with what I've seen when I pulled the four plugs out several times and verified consistent spark, and also saw consistent spark from the coil wire to a ground. Not sure if this is related to the tools in relation to the lower voltage 6v system or a weak coil, or maybe I'm not getting consistent spark when everything is in place and cranking.

[Rick Spivey]

Not sure I believe either of those test methods works great on a magneto. The only tester I've seen with a bulb in the handle was for testing 12V DC, or 120 V AC. Maybe this one is made specifically for a spark plug tester, but I am not familiar with those. Also, timing lights are a bit hit or miss with magneto ignition; you must typically use a 12V battery separate from the Cub for power, but then they will flash when they sense a spark.

However, assuming at least one of your methods is reliable, an intermittent weak spark will never crank a cub. You need to eliminate some culprits, such as a ground fault at the wire mounting stud that goes through the magneto housing, or a bad cap (wasn't it replaced?). If in doubt abut your test methods, use either the kind that makes the spark jump an air gap, or jump from the end of the wire to the block or other suitable ground.

[Clip]

Update: magneto cleaned and gaskets replaced, coil and plug wires replaced. Started up second crank!

[staninlowerAL]

Success is sweet!! Congrats and celebrate.