Vacuum Advance

144-250 cid Inline Six Performance

Vacuum Advance

Postby Adams » Thu Feb 18, 2016 10:49 pm

Hello--I hope everyone is well--I'd like to see some discussion of vacuum advance...in particular, how it needs to be used on a 144 six. My car has a Holley 1940 1V that was a dealer replacement for the original carb. However, it does not have the spark control valve. When I check the timing, it advances as the rpm's increase, as I think the vacuum is coming from above the throttle plate. However, there is no advance at idle, and spark does not retard when the throttle is opened quickly (load on engine). What should the advance characteristics look like? Should vacuum be acting on the dist. while at idle? Should spark retard when throttle is suddenly opened? I've read so much online which is contradictory. Some say vacuum from the manifold is the way to go, but wouldn't that advance the spark way too far at idle? Right now the engine idles smoothly at about 8-10 BTDC, and does not knock when accelerating, but am I missing some performance? I can't tell since the motor is so puny to begin with! Thanks
Adams
 
Posts: 136
Joined: Sun Aug 02, 2015 11:01 pm

Re: Vacuum Advance

Postby Adams » Mon Mar 14, 2016 12:48 pm

Well, Ive been experimenting...I found a rebuilt carb for my 144 that DOES have a spark control valve. I put it on, and when I checked the timing advance, it seemed to work correctly (advancing during speed and high vacuum, retarding during open throttle). However, in operation, I now had a lag (dead spot) when opening the throttle wide, so I put the old carb back on! Strange how the correct carb with the correct advance profile does not operate as smoothly...it may have given a bit more power, but I'd rather have no hesitation during acceleration. It should all be moot when I put in the 200 I'm rebuilding. (see my 200 Rocker post). Adams
Adams
 
Posts: 136
Joined: Sun Aug 02, 2015 11:01 pm


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