Small Engines (Lawn Mowers, etc.): Briggs Vanguard 9hp VERY Hard to Start, mikuni carb, woodruff key

Question
Hi,
I picked up for free a BCS tractor (like a Gravely, takes attachments) with a snow thrower attachment. Its pretty new but had some issues with the engine which I thought I fixed. The engine is a 9HP B&S Vanguard horizontal shaft, single cylinder with a Mikuni carb. The issues were:
- woodruff key sheared off on crank, caused bad timing.
I put a new key in and got the flywheel back to where it should be for proper timing.

- sparkplug wire had corroded end and was not giving spark.
I replaced the wire and now there is lots of spark.

- cleaned out the carb with a long soak in cleaner.

- New sparkplug and new gasoline

Now, I can sometimes get it to start, sometimes it only chugs and coughs once or so. It acks like it wants to start but won't quite get going. When it starts, it just starts right up and runs very smooth with plenty of power...i run it on full choke for 15 sec then shift to no choke and its runs smooth.
To try and get it to start, if I squirt a few drops of gas in the cylinder that doesn't work. It has 90psi compression. I can't figure out what it wants.
>spark yes
>compression, yes
>fuel, yes

I am missing something. Any ideas?

Thanks!

Tim  

Answer
Tim
you might be loosing compression as the engine heats, you could try some heavy oil, but that is only a duct tape fix. Another possibility is your coil is loosing spark when it gets warm. Check for spark as soon as it conks out on you (use gloves, the engine will be hot!)