Well it appears you are OK in the valve area. I doubt it is a fuel mix
problem on a non-turbo. It maybe, but that would be a first in my
experience. The next thing I would recommend is to check timing related
issues. The 1G timing can be set with a light. It should be 5 degrees BTC
when the timing connector is grounded (brown connector behing battery).
There are two possibilities here: you are off time or  the timing belt has
jumped a tooth (and you are really freaking off time). If your belt is old
or you went cheap on the last timing belt change (didn't replace tensioner),
you really could have slipped a tooth.

I would check the timing first. It is somewhat easier. All you need is an
alligator clip to ground the brown/tan connector behind the battery. Do this
with a hot engine. If you ground the right connector (there is a pump tester
back there too...I think) the check engine light should come on. Then
connect a timing gun up to number one (drivers side plug wire). Fire it down
on the drivers side and look for 5 degrees. If you read 15, you may not have
grounded the wrong connect, but you are probably OK regardless. This whole
proceedure is on www.vfaq.com last time I looked.

If timing is off you will need to loosen the cam angle sensor on the
passenger side of the head (12mm nut) and rotate it to adjust. The sensor is
a round bell that is probably green (copper). If it WAY off, you need to
check the belt. This part requires more work as you will have to remove the
timing belt cover (upper and lower) and all the accessory belts. Then you
will need to line up both cam marks and the crank mark to make sure you are
properly timed. If not, you will have to get dirty and do a timing belt. If
not, you are driving a grenade.