Tune Up

TOM-WA-

Ok I purchased a vacuum gauge and am going to give it a try



1. should the car be at operating temp first

2. should the vacuum advance be disconnected?



Keep jacking the timing up until you get all the vacuum you can get, then back off 1". Use the direct manifold vacuum for your gauge if you can, the line going from the intake to the vacuum pump instead of the one going to the wipers. The line going from the carb to the vacuum advance is ported and won't give you the right reading either. This almost always puts a stock Hudson distributor with the vacuum advance unhooked at 8* BTDC @ 1000' elevation.



When you get done with that, use the vacuum gauge to set your idle mixture. Turn the screws in lean until you notice the vacuum drop a bit, then richen it up until you get max vacuum again. Do that for each idle mixture screw on your carb. When you think you have them right, check the idle mixture screw again. Repeat until a 1/4 turn range causes a vacuum drop and recover. Now you are at lean best idle, the throttle response of your Hudson should be a tad crisper.



I love vacuum gauges.

RL Chilton

Tom-

Yes and No.

[Deleted User]

RL Chilton wrote:

Tom-



Yes and No.

Tom,



sorry I got busy and forgot to respond to your earlier question. Go with Russell's answer.



On #2, if the vacuum advance is connected in its stock location at the carb - its ported vacuum anyway. This means the throttle blade inside the carb has the vacuum cut off and is acting like its unhooked.



Not a bad little test to see if you are pulling a vacuum at idle through the advance canister line. If so, your throttle blade / throttle speed setting is too far. Its not uncommon to find an overly rich idle mixture screw setting being compensated by additional air being tuned in by cranking the idle speed screw too far. When the idle speed screw is turned too far, it will bleed a tiny bit of vacuum to the advance canister line.



A combination of low timing and overly richened idle fuel mixture can cause the idle speed screw to be adjusted too far and open up the vacuum port in the carb.



In this thread:

http://classiccar.com/index.php?option=com_jfusion&Itemid=62&jfile=showthread.php&t=18994&highlight=spark+timing



I have my own Hudson running off direct manifold vacuum with a quicker mechanical advance curve. In that instance, I don't disconnect the vacuum advance canister when I adjust it and go for maximum vacuum on the gauge. The reason you back off 1" with ported vacuum is because as soon as you crack the throttle blade - you're getting 7* of additional timing by the canister being brought in via the ported vacuum from the carb.



Happy tuning, keep those Hudsons rolling



Mark