There is a carb vacuum port that is used for the choke pull down diaphragm and it may be more variable than the manifold vacuum, could T off that and see what happens. Thanks for the suggestion. I will drive it around for while and see what kind of fine tuning it may need.

 

When I read 0 degrees timing I was wondering if that was a static timing. But you also reported 10 degrees. At what rpm are these timings?

Glad you got it running. Let us know about your mpg when you get a chance to check it. That will tell the whole story.
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I do believe it is static but yes the RPM can mess with timing and think why I asked.
The 10* BTDC would be after the static of 0* at RPM?

That is also why I asked of RPM and the timing jumping.
If it is just at that point of the springs / weights moving that could cause it to jump.
Dave ----

 

0 degs. was static timing, and the 10 degs was at a bit of high idle due to my missing that one big port on the 5 port vacuum line manifold open to the air making it run fast. After doing some more research, found out that as Fuzzface mentioned, there is quite a bit of difference of opinion on using a ported vacuum or a manifold vacuum to operate the advance bellows on the dist. Something else to play around with as I see how it is doing overall. It is advancing past an idle 10 degs as I run up the RPM, so that looks good. Now, after reading comments on Chinese made HEI units, remains to be seen if this one will last. Not sure if it makes any difference, but did get it from a speed shop. I bought this truck new in 1985, and over the years, the TFI module failed many times, so I always kept a spare in the glove box. I even had a cut down nut driver to get to the TFI mounting screws, as the fuel pump was in the way of a normal size one. When I bought this HEI unit, I also purchased the module that goes in it, just in case. Timing adjustment in the Haynes manual is pretty lame as it only refers to Durapark II. One other thing I did while I was rebuilding the carb, was remove the tamper proof cap off the idle screw just in case. In the whole project, that was the most difficult. I thought it might be a push down and turn type of lock, apparently not. I tried drilling it to put in a sheet metal screw to pull it off, as prying did not work. A sharp drill did not even scratch it...what is it, carbon steel? I finally resorted to a Dremel tool with a cut off wheel to get it open, but still had to use pliers to peel the rest off like opening a can of ham. You have to remove the idle screw to remove the base of it.

 

If you have a automatic transmission,, you will want to use ported vacuum. Problem is, you usually do not have ported vacuum on that computer style carb. Too bad you went to all that effort and money to rebuild it. With the computer carb you might be better off leaving the distributor vacuum disconnected.

 

Being you cant try ported vacuum, your carb dose not have that port, and you are already on manifold vacuum you can try as Dave said, remove manifold vacuum and plug it.
Now when you do this the timing will go back to 0* at idle RPM so what you will need to do it bump the timing up to 10* BTDC and see how it runs.
If you dont have pinging or kick back when starting when hot then maybe bump it up to 12* BTDC.

If you find the truck runs better with manifold vacuum then run it. If better with out manifold vacuum then run it without vacuum.
As much as motors are all alike, be it a 4 up to 8's they are also different even with in the same motor family.
That is why some like ported vacuum others manifold vacuum and yet others none at all.
So test each one and see what works fro your motor.
Dave ----