My 110 Blowby Problem Saga
The first thing one needs to check on this engine is the small orifice in the bottom of the cam box that connects to the vacuum hoses that connect to the intake manifold. This is easily clogged. I use a small drill bit to make sure it's complete cleaned out. You can clean it, you think, with a small wire only to have it clog again almost immediately if there's some sludge in your cam box. I plug the vacuum hose coming off the bottom of the cam box with a rubber stopper and look to see blowby coming out of the bottom of the cam box before I'm convinced I've got it cleared out.
In my case, this was not the problem. I had paid a reputable shop to do a ring and valve job on my engine, so I thought the rings would have been fine. I checked the compression, and found it roughly equal, albeit low (~110-120 psi) on all cylinders. I thought my gage might not be calibrated, but since the cylinders were within 10 psi that seemed OK. I ultimately diagnosed the problem by checking the level of intake manifold vacuum. I could not exceed 15" of vacuum at idle, no matter what amount of ignition timing advance I dialled in. This is a sign that I did not have good compression. The old rings were actually sealing better than the new ones, I think. All the cylinders had about the same amount of wear in the same place.
I removed the cylinder head and borrowed an ID micrometer from a machine shop. Low and behold, just honing the cylinder walls could not compensate for the 0.008" of wear in the cylinder walls. The maximum wear, as you might expect, was just below TDC where compression is highest.
My car is a grey market car that undoubtably had seen service as a taxi! I searched and found pistons that could handle 0.005" over, but not 0.008". When you look at the head gasket, you can see the bores are much to close together to bore them out more than 0.005". I then searched for another block that could use either my existing stock pistons, or the oversized ones I found.
I finally found a good used long block for $1500 and had that installed intact. Now everything is fine. The original rebuilder, who hadn't checked the bores for wear when they tore the engine down, did the right thing. I agreed to pay an additional $300 for their labor and consumables (oil, gaskets, antifreeze). They paid for the used engine. I'm running Castrol 5W50 100% Synthetic in the used engine for the past 20K miles. It uses about 1 quart in 3000 miles. It runs stronger and no oil in the air filter. I couldn't be more pleased.
I hope you find your vacuum hole clogged up, and not low intake manifold vacuum in neutral. Otherwise, you may be up for another motor.