1200 Died - No Spark
 

Hell everyone. I need some help with my 1200. I bought it sight unseen from auction last fall. Auction site had a video of it running and driving. Wouldn’t start when I went to pick it up. Got it home and it started after removing the bad air filter. New plug and air filter and changed all the fluids over the winter. Ran fine for an hour then struggled to do anything other than idle. Couldn’t tune the carb to make any improvements. Carb appears new. New coils and condenser and man it ran good! Rode it around the yard for 5 mins to warm it up so I could adjust the carb and just as I was coming back to pull it in - it died and wouldn’t restart. No spark. Put new points in it and still nothing. I have power to the coil and .5 ohms of resistance from coil ground to engine ground. Any ideas on where to go?

https://www.onlycubcadets.net/forum/showthread.php?t=11

Look at the link above for more test points/ procedure on the coil.

Also, Is the .5 ohm reading you have with the points closed? What about with points open? Should be no continuity there.

Yes .5 with the points closed. Points open no continuity.

Per the coil test link - here is what I got.
42.8k ohms resistance between coil + and -
I’m assuming the “tower” is where the plug wire goes - no continuity when points open. 11.38m ohms when points are closed
The last test - coil ground to engine ground is .3 ohms and coil positive to engine ground 43.2k ohms

Bad coil maybe? Odd thing is the old coil yields no spark too. Granted it didn’t run well with the old coil- but still had spark. Thanks for the response. Let me know if I didn’t perform any of those test correctly. Been a long long while since I worked on these old small engine systems, and this is by far the oldest thing i have ever worked on.

Coil test should be performed disconnected......that is..... +,- and spark plug wire removed. We don't want external factors to influence/interfere this test. If the external factors didn't influence your test, the coil is shot. Let's be sure. Tower is where the sparks are hiding.

There are certain factors that can cause coil to go bad.... one common factor is leaving ignition on without tractor running.

Do you have 12vdc at the + side of the coil?

If yes, do you have a spare condenser kicking around that you can try?

Ignition switch could be bad. To eliminate the possibility of a bad switch you can run a jumper wire from battery positive terminal to coil positive terminal while leaving all other wires connected. Then crank engine and check for spark. Sometimes the connections inside ignition switches lose connectivity in certain positions.
You can also try backing off on the switch rotation slightly while cranking. Sometimes if contacts inside switch get worn badly, if you back off on switch rotation that will let the contacts make a connection.

Coil test round 2.
New coil
No continuity between + and - on the coil
No continuity between + and tower on coil.

Old coil
4 ohms between + and -
8350 ohms between + and tower.

Seems the coil is junk.
Installed old coil with new condenser. SPARK!

But, it’s running how it used to. Idles ok but will die if you give it any fuel

Clean the carb?

I pulled the bowel and it was spotless. It looks to be a new carb.
The strange part it ran perfectly with the new coil for about 10 minutes. Throttled up no issues and ran great at high rpm. I will clean it this weekend while waiting on a new coil. The new one I got was a cheap Amazon 35 dollar special. I’ll order a Kohler brand in the mean time

Carbs generally have more than one "circuit" in them. There is almost always a low speed jet or idle jet of some sort. This handles fuel flow at low RPMs. There is often an Intermediate jet or mid range jet, that does just what it sounds like. There is almost always a high speed jet or main jet. Again, this is just what it sounds like.

If it runs at idle, but stumbles and dies when you try to rev up, and the carb adjustments are not out of whack, that is likely a clogged intermediate or high speed jet, depending on the individual carb that you have. It is possible that a needle is stuck. It is possible that a passage that feeds a jet is clogged. It is also possible that the float bowl has a fuel level that is too low. This can be caused by a sticky float valve, or a fuel feed problem. It is possible that you may have water in the float bowl with just a little fuel floating on top.

More complicated carbs may have an accelerator pump that would influence this sort of thing, but I don't expect to see one of those on simple motors.

It is also possible that you have an ignition timing issue or an intermittent wiring problem, but fuel issues have been the cause of this type of problem 95% of the time in the 50 years that I have fooled with small motors.