I have a B&S 16.5 HP engine on a riding lawnmower. I had the engine rebuilt last winter and it runs fine after it starts. The problem I have is that it turns over very slowly when starting. Once it does start, and I stop it (for example to fill it with gas) the battery runs down and it turns over so slowly it will not start again. I then charge the battery (I replaced the battery just a couple of months ago and had it rechecked - it is good) and then it will start up again (albeit cranking slowly). After trying to start it several times I checked the battery cables and they were hot.

I had the repair shop check if compression is building up in the engine due to the exhaust valve not being adjusted correctly - they did a manual check by turning the mower by hand and said it is okay. He found that the base of the engine mount (a steel plate) was loose and suggested that it was not sufficiently grounded. I tightened up all of the bolts and thought that it was solved but still ended up having the same problem.

I am pulling my hair out - any ideas are appreciated.
Thanks.

Hi,
First I would check the charging circuit. Check AC out of the alternator (28-36V) and the DC out of the rectifier (14.5V) to address your problems with the battery. I would not be surprised to learn that the rectifier has shorted and putting AC into your battery, the kiss of death.
I think your cranking slow is the result of a weak starter; probably has some shorted turns on the windings.
Not unusual for battery cables to heat up, though if you see melting that would be a bad sign.
Peace,
Clarke