Leak valves - what do you think?

Hi guys,
I've read a few places that to test your valve's seal to put some mineral spirits in it overnight and make sure it doesn't weep out.

A guy that builds drag racers at work also told me that head shops usually vacuum test them.

Here's my issue. I had a bike eat a toothpick sized pin (from the darn choke flaper). The valves are straight and we just lapped the valves. Everything looks fine. I decided today to take a rag and wrap it around my air gun on my compressor, set at 100 psi. I shoved the gun in the intake and exhaust ports. The two valves that I worked on both leak...a tiny bit. The other cylinder was running fine, but figured I'd take a peek. The exhaust was tight, but the intake leaked worse than the two I worked on.

So...will this get any better with time (like does the valve wear into the seat a bit?) or will this improve when the motor is warm? If the drag race guy only does vacuum test, thats only 14.7 psi "pushing" into the cylinder. I was using 100 psi, sure with some leaks, so say 50 to be safe...

Thoughts?

If you were pushing 100 psi of air pressure on the back of the valves rather than the face it is possible the pressure was just pushing the valve open a tiny bit and letting the pressure leak through. Ed

Was air applied through the spark plug hole or intake trac?

Intake. Head was off and on the bench

put head upside down, fill combustion chambers by ATF and check every 5-10 min.
Good valves will hold ATF for at least 1 hour.

I know your tight on money, but the head really needs to go to a machine shop. Unless you know someone in your town with the correct tools, who knows how to use them. Look in your manual, and see what dimensions it calls for for your valve seat Face width, valve face width, valve margin, etc. Look close at the pitting on the seat and the face of the valve. You need to check the valve Guides, then re-cut the valve seats 3 angles, grind maybe replace the valves, and get the correct installed height for the shim range and spring pressure. Don't forget New good quality stem seals. Any bolt hole threads or other damage can be repaired then when its apart.

No need to go to machine shop, if you can check cracks/flatness/valves/valve seats yourself.
I do it every time. Probably 95% of heads don't need to be sent to machine shop.

I was taught to coat the port around the valve seat with an acetylene torch with the O2 shut off, then position the head level with the combustion chamber facing up, then fill the ports with kerosene and let it sit overnight. The slightest leakage causes the carbon coating to turn shiny black, and the only acceptable condition was zero leakage after 16 hours.