How far should timing actually be advanced?

[200ci66]

Alright, instead of starting another thread I figured I would go ahead and ask something on here since it's closely related.

I don't BELIEVE my vacuum advance is working. Whenever I plug the vacuum line, the timing mark doesn't move. It doesn't seem to make a difference as to whether it's on the line on the distributor or not. It DID work on the old distributor (moved the timing mark by 2-3 degrees). I was thinking maybe my advance unit is either out of adjustment or no good. Is there any way to adjust the vacuum advance, or is there anyway I can use the advance unit from my old 66 distributor?

I'm getting a hesitation when hard accelerating from a dead stop, this might be carb related, but since I'm noticing it a lot more lately I figured I start with something that I've recently changed.

 

[Explorer]

68 distributor and non-SCV carb: Using ported vacuum for distributor will not affect timing at idle. Only when throttle is opened that it draws vacuum.

 

[66 E100 Pickup]

I don't BELIEVE my vacuum advance is working.

Very easy to check it, get a 3-4 foot length of vacuum hose, connect it to the canister, remove the top of the distributor, and suck on the hose. The rotor/plate should move, and you should get a solid resistance while sucking (no blow through).

It seems that vacuum canisters do not last very long anymore. The rebuilt duraspark unit I run lasted about 5 years. Others have said they only get 1-2 years from a new canister.

A hole in the vacuum canister will definitely give you a big stumble off idle, and low power. Dying in an intersection, etc.

John/Fresno

 

[200ci66]

Hmm.. well it doesn't seem that's the problem. It DOES move. Looks like it's time to move on to the fuel system and look into rejetting the carb.

 

[FalconSedanDelivery]

Vacuum advance contrary to many long winded stories on the internet , do not contribute to better acceleration or part throttle response , UNLESS the mechanical curve is WRONG,In the early days of performance up till the mid 70's a Dual Point Dist ( NO VACUUM ADVANCE ) was used on many of the performance engines from the factory , Vacuum advance was invented for 2 reasons , First to get a bit better fuel economy , and later to reduce emissions, NOT for drivability or performance , when tuning a combo do it with the Vac disconnected , just like setting initial timing , afterwards hook it up and see if it helps , there are many different Vac canisters and they come in at different inches of Vac and allow different totals , all of this is part of a Dist Recurve , just picking one part and saying its moving proves nothing , when you by a reman unit it is NOT optimized for anything , it will function , and many times on a OK level , BUT never a Optimum level. I cant teach Dist recurving , by typing a few paragraphs , that would only be a 3rd of the equation , how , plus why , plus experience is needed along with the proper equipment , adding a spring , bending a tab , welding up a slot , is part of how , not all of it

 

[200ci66]

^ All good to know. Thanks a lot for the info FSD.