Backfiring??

[Mainemann77]

Hey there Cub Crew! I have what seems like a dumb question, but here we go. My '75 Cub 1000 way running fine until I spun the PTO. So, I changed out the PTO, assembled everything back together, gapped the assembly with feeler gauges, started her up and engaged the deck. It bogs briefly sends out a huge backfire then runs. I'm aware of the usual suspects of backfiring and I'll check them accordingly, I also tensioned the belt according to specs, but I suppose my question is, why is she backfiring now and not before the PTO change?? She has never backfired for me, not ever. Why now??
Thanks y'all
Scott

[ol'George]

Originally Posted by Mainemann77

Hey there Cub Crew! I have what seems like a dumb question, but here we go. My '75 Cub 1000 way running fine until I spun the PTO. So, I changed out the PTO, assembled everything back together, gapped the assembly with feeler gauges, started her up and engaged the deck. It bogs briefly sends out a huge backfire then runs. I'm aware of the usual suspects of backfiring and I'll check them accordingly, I also tensioned the belt according to specs, but I suppose my question is, why is she backfiring now and not before the PTO change?? She has never backfired for me, not ever. Why now??
Thanks y'all
Scott

Try adjusting the main jet 1/2 turn to the rich side (CCW)
report back

[Mainemann77]

Hey there ol'George thanks for the reply. I tried a 1/2 turn on the main jet, the backfiring seems to have gone away, however, she doesn't seem to be running top notch, and eventually surges and dies down under load (with pto engaged). I tried dialing in the air mixture, attempting to find the "middle" between rich and lean but there did not seem to be much difference there; I was listening for idle deflection on both the rich and lean sides. I suppose this carb got gunked up?? Because really, most of this came on out of nowhere. So, how do I go about disassembling the carb for a clean out? And is cleaning it out recommended?? Please help! Thanks y'all
Scott

[ol'George]

Set the main jet first.
Then at idle, set the air mixture.
Then go back and see if you need to tweak the main jet again.

if no joy, count the turns of the main jet as you gently seat it, so you know where you are at.
do the same to the air jet.
Then
remove both (don't loose the springs on the needles)
Blow into the holes where you removed the needles, with your air hose.
Then return the main needle and air jet back to the settings you had, and see how it runs.
Sometimes that trick works, saving you removing the carb to clean it.

[Mainemann77]

Thank you so much George, I will give that a try. Also, I should be setting the carb at low idle, correct?

[ol'George]

No,
Set the main jet at wide open governed rpm.
The air bleed is set at idle.

[Mike McKown]

I had a single cylinder Kohler do that to me one time. Took me a season and a half to figure out the breaker arm tension on the points had given way and was too weak. Changed the points and problem went away.