I have a 67 with it's original motor 350 hp. I checked my timing, dwell and vacuum today. My dwell was set at 12 and my timing at 5 degrees. My vacuum was 14. The booked showed that timing should be 10 degrees and dwell set to between 28 and 32. I reset the dwell to 30 and the timing to 10 degrees but my vacuum remained the same. I also adjusted the original carb. The car is running better but I would just like for someone to confirm that these setting are correct.

Thanks
Jay

 

Hi jay
Dwell at 30 and timing at 11 BTDC is a lot closer to the factory 350 HP settings so no wonder it's running better. Next step would be to see what vacuum can is on the distributor and go from there. There are some tweaks you can do for the total timing map to improve performance. Search for posts by Lars or our own john hinckley. They have some great stuff on mapping timing.

 

Will do. Thanks John

Jay

 

Jay:

Just be sure your dwell meter and timing light are working correctly. Having a dwell of 12 degrees is almost unheard of. Sometimes the meters can go bad with advanced age. Being 18 degrees low on dwell, means that coil is not getting a full electrical charge, and also 18 degrees of dwell variation from spec can result in timing being increased the same amount (18 degrees). This is if it changes that amount and the timing is not re-adjusted to reflect the change. It sounds like your timing was re-adjusted back to 5 degrees for this very reason.

Lars and a few others (65tripleblack, Mike M and Critter-1 ) (RIP guys) did a dwell vs timing study here on CF back in December 2016 and it was 1 to 1 on dwell change versus timing advance change.

Vacuum needs to include the engine RPM at the point the vacuum is taken. Without RPM, the vacuum number does not mean as much. My 327/350 HP (67) is typically around 17-18 IN HG at 900 RPM (my normal curb idle), but will drop off as I lower the RPM down to 700-750 RPM. But I can't tell you what that number is at this time.........but probably around 14-15 IN HG at the lower RPM.

Make sure initial timing is set at 500-550 RPM (or so) and that you do not have centrifugal advance kicking in. Also no vacuum advance. The engine will not like this low RPM, so set the timing and then quickly increase it back up to above 700 RPM. Between 550 RPM and 900 RPM, my distributor will add about 5-6 degrees of centrifugal advance. I know this, so I adjust/compensate for it when setting initial timing.

Larry

 

look at these threads:

​​​​​​https://www.corvetteforum.com/forums...-overhaul.html

https://www.corvetteforum.com/forums...l-economy.html

Duke​​​​​​

 

Thanks guys for all of this very useful help. I think that I am on the right track as it seems to be running better. This Forum Rocks.

Jay