Machine Gun Full Throttle?
 

I got my 1250 back up and running for about 30 mins after pulling the engine, replacing the oil pan with one that didn't have bolts sheered off in it, replacing the flex coupler and centering bearing, setting valve clearance (3 times now), replacing the plug wire, coil, points (used from my "parts" 1200), solid mounting the engine, and swapping on the carb and regulator from my 1200.

Ok, bear with me...

1250 K301 with the carb from a 1200 K301, standard 12V automotive ignition coil, runs 30 mins, coil stops working (tested good this morning). Repaved ignition coil with brand new of the same type, but added a resistor inline on the positive side of the coil. This new coil died 30 mins later. Found the old Diamond LB-85 coil and has been working just fine without the external resistor...however...

It seemed like the valve timing was off or the 1200's carb running wasn't up to snuff for the hydro transaxle. I put the original carb from the 1250 back on it, adjusted the valves for the 3rd time thinking maybe I'd done it incorrectly. I swapped in a new NGK spark plug.

The new problem I'm having today is that when the K301 is opened to WOT, it shoots blue from the exhaust (no muffler) and stumbles. When engaging the PTO, it trips over itself and sometimes never recovers. I cut some grass with it and it starts to fall on its face after a minute or two like it's going to die, so I stop and it comes back from the brink. It will idle much better than it ever has before now, but WOT is something it just can't do. It behaves the same way with both carbs, both spark plugs, before and after the last valve adjustment.

So what am I doing wrong here? Anyone have any insight to shed some light on this situation? Thanks!

Cub Cadet used the same engine in both the 1200 & 1250, that being K301AQS-47541.

Would that be Blue Flame or Blue Smoke..??:bigthink:

I have no clue why you keep adjusting the valves. Timing is achieved by adjusting the "point gap". It should be .020" or less.

You might one to try to correct Ignition Coil.

Currently running a Diamond LB-85 that was on the 1200's K301 for over a decade with no problems. I can't afford an $80 Kohler coil. In reality, I can't afford much at all right now.

That blue from the exhaust would be blue flame (backfire from exhaust).

I keep readjusting the valves because I kept thinking I did it incorrectly, as stated above.

Points gap has been set at .020"

Timing didn't seem to be off until I switched back to using the internal resistor ignition coil.

What Roland said..... plus look into a lean running condition. Your description sounds like fuel starvation.

My 1450 runs better at .018" point gap.

See above recommendation.

Static time the engine.
Use the correct coil, condensor and plug.
Head bolts properly torqued?
Plug wire good?
Carb adjusted correctly.
Good fuel flow to the carb?

I adjusted the carb every which way because that was my first thought as well. Low idle is spot on with both carbs. I went back to the original carb for the 1250 because I had it tuned a bit rich on the top end, but nothing changed in running results, so I can only assume it's not the tune.

Could it be the coil not keeping up at full boogy? The standard automotive coils kept up for the whole 30 minutes that they worked. Found out that they are about 1.8 ohm resistance and the ballast I ended up with isn't a high enough resistance to make up the difference to get into that 3-5 ohm range. But even then, with the 12V - no resistor coils, it would pull hard at WOT and occasionally sounds like it was coasting downhill for a second. Think of driving a vehicle with a manual transmission downhill, in high gear with your foot off the pedals (compression braking in way to high of a gear).

Replied in red

There is one other thing I'd like to add....

Condenser..... Is it good? And is it attached to negative side of coil?

It's a big deal at higher rpms.....