360 surging

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moparmucelli

moparmucelli

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hi guys I’m just giving an update I had a surging problem a while back and I was messing around with the vacuum advance and I had it plugged into the manifold vacuum and I took it off and plugged it into the portal vacuum and it seemed to run better why did it affect it so much?
 
Sounds like you have a touchier than normal carb or distributor...at least that is my guess. maybe one of the carb experts can tell you more.
 
Surging under a light load with a steady pedal is usually caused by a lean condition. Switching from manifold vacuum to ported vacuum will typically reduce the amount of your total advance across the RPM range.
It never hurts to put a timing light on and see where your total advance is and at what the RPM. You would want to do this with and without the vacuum advance hooked up.
Of course this will require a timing tape on your balancer or a timing light with advance features.
 
Plus the vacuum advance may be the cause of it, as a change in advance will cause a change in rpm, at light throttle openings.Plus it will change the manifold vacuum in so doing, and that will definitely cause carburetor fueling changes.
 
There are already 2 other topics about the subject, this makes the 3rd.
I appreciate the followup, but can we just keep/merge this into one topic please, maybe have the other ones locked and pointed to this one?
 
AJ/FormS said:
Plus the vacuum advance may be the cause of it, as a change in advance will cause a change in rpm, at light throttle openings.Plus it will change the manifold vacuum in so doing, and that will definitely cause carburetor fueling changes.
Click to expand...
Oh ok I see yea it seems like it changed it for sure
 
On the sparkport, the vacuum supply to the can is varied in accordance with the throttle position, and often it can take 1400 rpm or more at very small throttle openings, to activate the can at all. This can be good or bad depending on the rest of the engine and it's tune.
To see it in action just Tee a gauge into the line and and take it for a ride, watching the gauge.
 
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