Small Engines (Lawn Mowers, etc.): 8hp Briggs hard to start in cold weather, old briggs, synthetic 5w

Question
QUESTION: Hi,
I have a 8hp Briggs engine in a Simplicity 728 garden tractor. Model: 191700. It is a shortblock which is an I/C model. The problem I am having is that when the temperature is below 20 degrees it is very difficult to start. Above 2o degrees it takes a bit but it will start. What I have done so far is, bought a different carb (throttle shaft wore into the body on the old one), Changed the oil to synthetic 5W-30, checked the flywheel key, new spark plug (NGK B2-LM) gapped at .30, cleaned the carb twice, drained the fuel and refilled with fresh, cleaned the air filter, cleaned the carbon out of the cylinder and around the valves, new head gasket, check valve clearences which are in spec, and has strong compression. The problem is when I give it a pull with the choke on it fires then open the choke and pull again and it fires and does 2-3 revolutions but that's it and then it does that 3 more times then needs the be choked again. When the temp is above 20 degrees I have to take off the air filter to start it but put it back on to get it to run nice. Once it has been running it will start up on 1 pull and runs like a swiss watch.

ANSWER: Those old Briggs engines have always been difficult to start when cold.  Good call on the oil, 25 years ago when I was a kid synthetic didn't exist...Dad just had up keep pulling the starter rope until the engine warmed up enough to keep running.

Briggs sells a couple of block heater for late model engines but I don't believe you engine can accept the heaters but take a look for yourself at the link below:

http://www4.briggsandstratton.com/miscpdfs/RNT/Accessory%20Catalog%20ms3880.pdf

Will the engine run on the second pull with the choke 1/2 open 1/2 closed?

Eric

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QUESTION: I have tried 1/2 choke and just slightly cracking it open but it doesn't make a difference

ANSWER: To help troubleshoot the problem you need to know if the engine is running lean or rich.  Lean conditions are easier to identify because you can richen the fuel mix using several techniques.  You will need to remove the air filter.  With the air filter removed, you can hold you hand over the carburetor throat blocking all the air from entering the carburetor.  This is produce a very rich fuel mix.  You can also use starting fluid but I have read where some folks have experienced engine damage using starting fluid.  A safer priming fluid is just to use gasoline in a small squirt type container like those old diner style ketchup bottles with the tapered tips.

If you think the fuel/air mix is too rich you can lean it by introducing more air into the carb.  The easiest method I have found for introducing more air is to remove the air filter and then use an air compressor to blow more air into the carb throat.

I would think, based on engine theory, the engine is too lean in the cold temps.

I forgot to ask, are you using points or an electronic type ignition system?

Eric

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QUESTION: When it does run I've adjusted it so it is slightly in the rich side but it still runs smooth and accelerates smoothly. This is has a Magnetron solid state

Answer
Try setting the plug gap to .025.  Is the ignition coil gap set at .010?

The Magnetrons are very reliable so the difficult to start when cold is not likely to be an ignition problem.  You stated the valves clearances are in spec.  Do you recall what the intake and exhaust clearances are gapped at?

Eric