Backfiring when tring to start

[Tomreen1]

I have a z225 johndeer with a 18.5 Briggs and Stratton engine it was smoking and blowing oil at the end of last summer so before i used it this year i got into it found a blown head gasket we replaced it and put it back together ran great no smoking only ran it for about 20 minutes and parked in garage overnight it leaked gas over foor it only had about 1.5 gallons in it but it was all on floor put on a new carb now it back fires when i try to start could i have accidentally changed the gap between the flywheel and the mag(i guess that's what it is)if so how do you reset the gap i can get feeler gauge if that's what it takes

 

[able43]

Old trick I learned from an elder... average business card is fine to gap the magneto with. Also worth noting, double check the flywheel has it's key weigh and is aligned properly to ensure ignition timing. As for the carb sounds like you might have it squared away but here is some food for thought if it isn't. Install an in-line fuel shut off valve between carb and fuel tank. Shutoff after each use.

 

[Tomreen1]

Old trick I learned from an elder... average business card is fine to gap the magneto with. Also worth noting, double check the flywheel has it's key weigh and is aligned properly to ensure ignition timing. As for the carb sounds like you might have it squared away but here is some food for thought if it isn't. Install an in-line fuel shut off valve between carb and fuel tank. Shutoff after each use.

We used a business card (well ok my grandson did the work) whenwe put it back together the first time i thought i was a little thick but it did run so maybe it just got knocked lose i will look tomorrow thanks for the reply

 

[bertsmobile1]

If you took the flywheel off, then remove the bolt & check that the key has not fractured, actually, check the key regardless as a decient backfire can shear it.
Was there a lot of crud around the barrel because overheating can casue the valve guides and or the valve seat to shift & that will cause backfireing during cranking.
Where was it backfiring from, the carb or the muffler
Where was the ful coming from that you found on the floor ?