I have a Briggs 18hp on a Craftsman Lawn Tractor that runs great except for one thing. When starting when cold, it almost seems like the battery is weak. It has been like this since new and is much worse in cold weather. When you turn the key, the engine seems to be under compression and won't hardly turn over. Several times, I have had to jump with a full sized car battery and even then, it seems to turn over hard. Once it's started, it starts just fine. My question is this... Is there some kind of compression release that might be sticking? Kind of like a compressor so you won't start under a load. Any other ideas. One more thing. Sometimes when it does start, after several tries, I get a loud backfire.

I have a Briggs 18hp on a Craftsman Lawn Tractor that runs great except for one thing. When starting when cold, it almost seems like the battery is weak. It has been like this since new and is much worse in cold weather. When you turn the key, the engine seems to be under compression and won't hardly turn over. Several times, i have had to jump with a full sized car battery and even then, it seems to turn over hard. Once it's started, it starts just fine. My question is this...Is there some kind of compression release that might be sticking? Kind of like a compressor so you won't start under a load. Any other ideas. One more thing. Sometimes when it does start, after several trys, I get a loud backfire.
When its cold the oil gets really think so it turns over hard, or is it in your garage? If its in our garage I don't know. The backfire is just from ranking it so much there is a lot of gas in the head.

It even did it during the summer, except it is worse now that it is getting colder. I would agree with you that the oil is the cause for getting worse when cold.

I'm going to say, check the oil breather assembly. This is especially worth looking at if there is any oil film in the air cleaner.

This engine has a paper filter cartridge for air cleaner and I have already installed a new filter when I was servicing. If there is another oil filter assembly let me know.

It's not a "filter" per see, but if there was oil in the air cleaner, then the oil breather is suspect.

Look for a rubber tube that hangs down from the crankcase that's open. It's usually on the carb side of the engine. This allows the crankcase to breathe and normally has a non-replaceable filter in it similar to what might be found on a window AC unit. The plate that's attached to the engine and the tube can be removed and cleaned.

Since this is a Briggs engine, posting the data from the plate or even the Craftman model number will allow us/me to identify the part. Go to Welcome to the Parts Store (http://www3.sears.com). Look up the model #. Then look up the engine number. Then look up the engine. Look at the parts list for the word "breather". Alternatively you can use www.briggsandstratton.com.

Hmm, I would check the valves. And the compression release is on the camshaft. But I would suspect the valves are out of whack.