Low idle vacuum on a freshly built engine

[70bigblockdodge]

You want .040 of the transfer slot showing under the throttle blade. Old trick on a holley was to crack rear blades open with the stop or drill a hole in the primary blades across from transfer slot.

 

[superfragl]

What does drilling a hole do? And where exactly do drill?
Would drilling a hole allow more air through and therefore reduce the vacuum? Sorry for all these questions - just trying to understand.

 

[70bigblockdodge]

Allows more air so that the throttles are in better position on transfer slot. In your case I would not do this to a really fresh engine as you stated above. Drilling a hole in the throttle blade is a commitment and I do not think your cam is big enough to jump at this yet. Go put some miles on it, see if it settles in, 10" is not bad just don't pump to pedal as you come to a stop, you will use up your vacuum.

 

[superfragl]

Maybe that`s the way to go..
I will also try advancing ignition at idle to 20-25* to see if that improves vacuum reading. Some folks say their engines are happy with that much initial advance.
I did try 16-18* previously with no success though.

 

[superfragl]

Update. Tweaked ignition last night. Ended up with 22* advance at idle and reading 14" of vacuum at 750RPM. The vacuum will drop to 11" when in gear. Starts fine with no kickback. If I bring RPM up by 150 I gain another 1" of vacuum and if I advance ignition to 26* I gain one more inch, but for now I will leave it the way it is.
Now I have to weld the distributor slots to limit the total advance. Anyone has an idea how much to weld? I have to remove 10* from the slots.

 

[65sporty]

How much advance does it have now? If it's 20 and you close the slot by half it might get you 10 but I think it will be a lot of trial and error. Are you going to mig it or braze it? The brazing will be easier to remove because it's softer.

 

[superfragl]

It is 26 now. I have to consider the diameter of the pin as well. So if I have .44 slot length, taking half of it out will leave me with .22 which almost equals to pin diameter, therefore this will not be correct. I will tig it. I have a small milling machine so cleaning up the slot is not a problem.

 

[70bigblockdodge]

Weld too much then grind/mill since you have it, to make final adjust.

BTW did you have any stumble when timing was only at 15. My Challenger has a stumble and sometimes a stall since new engine I believe it is in Carb just asking.

 

[superfragl]

Tough to say if it had any stumble. I did not road test it yet. Just put registration on her yesterday.