1957 shooting plugs

[Lionel]

Hi, I’m running a Holley 465 cfm on the 312 in our 57. It has 57 jets which appear to be to much as the plugs tend to get a bit sooty after slow round town driving. The motor does not use any oil. The carb has been rebuilt with new power valve 6.5, gaskets etc. and the float level set. The inlet gaskets have been renewed and the heater passage under the carb. blocked and the butterfly valve in the r/h exhaust has been remove. I have fitted an MSD drop in distributor and the timing is 14* advance at idle ( no vacuum) Has anyone had similar issues ?

 

[Douglemmo]

Hi,
Slow around town driving is not an acceptable way to judge carburetor jet size. Run the car at higher speeds (ideally full load), shut the engine off and inspect the plugs to determine if they are properly sized. 14 degrees at idle sounds to advanced to me, I believe the recommended advance is 6 degrees. If you have a question about what size jets you are suppose to have in your Holley, the appropriate timing and spark plugs, the best way to get all of this running together properly is to have the car dyno tuned where they can measure horsepower and air-fuel ratio, at load. The only problem is that most of the dyno shops that I found do not want to work on older carbureted cars. But I did finally find one and had my Mustang dyno tuned. They confirmed the distributor advance curve, initial timing and found that I was off many jet sizes.

Good luck

 

[55blacktie]

How does your car run otherwise? Before changing timing, jets, etc., try spark plugs with a higher heat range. At what elevation do you normally operate your car?

 

[Ward 57]

The CFM size sounds about right. If you have the shop manual I was surprised at how many different recommendations there were for the proper jets whether you were at sea level or up in the Colorado Mountains. I'm no carburetor expert but that's where I would look also. Many shops jet them for the most power but there are many threads on here about over carbureted engines.

 

[paul5456]

14 degrees initial advance is ball park for a 312 Y block. The factory setting is much lower, but the Y's seem to run better between 10 and 14 degrees.