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Old 03-02-2011, 02:32 PM
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using vacuum gauge to set timing

I just finished setting timing on sd 220 six. As there are no correct marks to go off of on rear of engine other tdc. Once vacuum gauge set into intake manifold below carb, engine now runs much better on todays gas. Set to max vacuum adjusted carb and now ready to run vacuum advance direct unported. has anyone opionions on this procedure?

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Old 03-04-2011, 12:38 AM
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Vacuum gauge used for timing

I have done exactly what you did but the particular engine I was working on actually ran better if I adjusted the distributor to maximum vacuum, and then turned it back the other way to read one less than maximum. The engine I was working on was a 327 Chevy small block. This may or may not work for you but you might try it. I did a lot of experimenting and the one less than maximum setting worked the best for me.
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Old 03-04-2011, 09:32 AM
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i dont doubt you optimized the engines running but you didnt set the timing.....why not verfiy TDC by mesuring it in the cylinder using or making a tool for this and then use a dial back timing light?
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Old 03-04-2011, 12:20 PM
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The method sounds good to me. The timing was set, just used a different method to measure it.
Really, on old engines, I see no problem with advancing the engine until it knocks, and then retarding the timing a little bit, to be safe.
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Old 03-04-2011, 12:48 PM
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timing

Ok, I got out trusty ol timing light and checked timing w/o ported advanced hooked up. Flywheel mark to left (retarded) of tdc mark in eng. Just noticed a circle on timing opening. Timing mark is in middle of circle. Timing recommended at 2 deg btdc. Good idle about 750 rpm. Reconnected ported vacuum and noted no change in idle. vacuum gauge reads 17. took for ride and noted performance. Switched over to manifold vacuum and idle now at 1000. I did not lower at this time. I took for ride and noticed better throttle response but no increase in vacuum gauge readings at speed, 4th gear 50mph about 10,11 on gauge. Does this sound correct? Or should engine vacuum readings reach closer to 15 at max tune.
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Old 03-04-2011, 01:42 PM
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When the throttle is opened, ported vacuum should be about the same as manifold vacuum. The port for ported vacuum is located just above the throttle plate, at idle, and when the throttle plate moves, the port is now below the throttle plate.
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Old 03-04-2011, 01:43 PM
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not sure of the specs on your engine ......but generally speaking set timing and then pick either of the two vacuum ports that the car likes the most, drive it to tell.....then go back and set idle speed and fuel air ratio tweaking it as you go. use the vacuum gauge to fine tune fuel air ratio go for the highest vacuum reading you can get
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