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Erratic spark on my '48 Cub

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ktroutman
10+ Years
10+ Years
Posts: 3
Joined: Mon Jun 07, 2010 3:10 pm
Zip Code: 17543

Erratic spark on my '48 Cub

Postby ktroutman » Sat May 27, 2017 12:59 pm

The Cub just stopped while I was mowing last week. It was just about time for a tune up so I changed the plugs, wires, cap, rotor, points and condenser. I installed the points with a .013 gap. I still can't get her to even think about starting. I have the magneto and square coil set up with a 6 volt positive ground battery. The spark going to cylinders two and three appear to be fine. Cylinders one and four have weak and sporadic spark. I didn't think this was a coil issue because good spark is getting to two cylinders. I am stumped. Any suggestions on what I should check next? Thank you

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staninlowerAL
10+ Years
10+ Years
Posts: 4975
Joined: Fri Oct 29, 2010 11:34 pm
Zip Code: 36558
Tractors Owned: Cubs: (3)'49's, (1 is for parts), (1)'57 IH Cub LoBoy w/FH, (2)154 Number Series Loboys, (1 is for parts), '76 Longstripe w/FH, Mowers: C-22, Bush Hog 412, Pennington 59, Woods RM42CF, Woods 42, assorted FCub plows, planters, discs, etc. OTHERS: '49 AC B & Ind. Sickle mower, '61 AC D12 Ser 2, '52 8N, '56 Ferguson 35 Deluxe, '47 & '49 Avery V, '53 MM BG (offset), '51 JD M (regular), '56 JD 420C, with Blade and fire plow, '85 JD 850 (Yanmar) w/72" belly mower, '76? Yanmar 2TR15 1500 & Bush Hog SQ42S-2 mower, '78? FORD Dexta, '86 FORD LGT14D & 48" Mower, (2)Cub Cadets & Mowers (MTD), (4) Sears Surburban's, other MTD mowers, Jeeps & other misc. "treasures"
Circle of Safety: Y
Location: AL (Southwest)

Re: Erratic spark on my '48 Cub

Postby staninlowerAL » Sat May 27, 2017 1:07 pm

Did you do the "tune up" with the mag on or off the tractor? IMO, recheck everything you changed/removed. A few month ago John in MO posted about a similar problem and finally diagnosed it as a weak impulse coupling. Yours could have weak/broken spring, some of the mag guru's will probably chime in on that issue.
Stan in LA (lower AL)
USAF & Reserves, Reg ARMY, ARMY NG (AL)

ktroutman
10+ Years
10+ Years
Posts: 3
Joined: Mon Jun 07, 2010 3:10 pm
Zip Code: 17543

Re: Erratic spark on my '48 Cub

Postby ktroutman » Sun May 28, 2017 11:15 am

I did the tune up with the magneto on the tractor. I have never removed a magneto so any helpful hints would be appreciated.

staninlowerAL
10+ Years
10+ Years
Posts: 4975
Joined: Fri Oct 29, 2010 11:34 pm
Zip Code: 36558
Tractors Owned: Cubs: (3)'49's, (1 is for parts), (1)'57 IH Cub LoBoy w/FH, (2)154 Number Series Loboys, (1 is for parts), '76 Longstripe w/FH, Mowers: C-22, Bush Hog 412, Pennington 59, Woods RM42CF, Woods 42, assorted FCub plows, planters, discs, etc. OTHERS: '49 AC B & Ind. Sickle mower, '61 AC D12 Ser 2, '52 8N, '56 Ferguson 35 Deluxe, '47 & '49 Avery V, '53 MM BG (offset), '51 JD M (regular), '56 JD 420C, with Blade and fire plow, '85 JD 850 (Yanmar) w/72" belly mower, '76? Yanmar 2TR15 1500 & Bush Hog SQ42S-2 mower, '78? FORD Dexta, '86 FORD LGT14D & 48" Mower, (2)Cub Cadets & Mowers (MTD), (4) Sears Surburban's, other MTD mowers, Jeeps & other misc. "treasures"
Circle of Safety: Y
Location: AL (Southwest)

Re: Erratic spark on my '48 Cub

Postby staninlowerAL » Sun May 28, 2017 2:59 pm

Did you remove the rotor and pinion gear? If so, check to see if they are in time (timing marks aligned). If you want to remove the mag for maint or repair, follow the instructions in service manual GSS 1012 ELECTRICAL EQUIPMENT, "QUICK LINKS" at the top of this page. Pages 1-6 is for magneto.
Stan in LA (lower AL)
USAF & Reserves, Reg ARMY, ARMY NG (AL)


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