My '71 bus (1600 DP) is getting reduced mileage lately. Seems like it began
after I had a whole bunch of work done, including replacing the intake boots
and the engine seal (i.e. the engine was dropped), plus valve adjustment and
oil change. Runs cooler for sure, but mileage is definitely less. It had a
tune-up about 1200 miles ago. Compression is good all around. No smell of
fuel at any time.

One other symptom, also new: on cold starting, it turns over reluctantly and
then doesn't start firing on all cylinders until ~5-10 seconds have passed.
Runs fine when warmed up. 

Yes, I'm in California with its new "cleaner"  lower-mileage gas, but I was
running that gas before this problem developed. I use either mid-grade or
high-octane.

What should I check? What to look for? Muir doesn't say anything about this one.

Thanks.

Steve Tokar