Vacuum Advance

[gberkin]

Does anyone know how to check to see if there is a problem with the vacuum advance on an HEI distributor?  Is there some kind of test that one can do to isolate problems with the unit?

Thanks

[Lt.Del]

Sure, hook her up to a timing light.  Keep the vacuum line on the advance.

Idle your engine while seeing where the timing is on your markers.  Have someone, or if your arm is long enough and you have a carb, give it gas.  

Tach her up to about 2k rpms quickly and see if your marks move (advance).  They should look like they jump.  

Hope this helps

SgtDel  

[Lt.Del]

Another thing is kind of common sense, just look inside  your distributor and manually try to see if the guts (springs, weights, etc.) will move freely. They should move just a tad.  You will know if they are frozen. Ensure there is not alot of rust looking powder all around.

Take your vacuum line off and after manually advancing the guts of your distributor, put your finger over the little tube that  the line connects to (trapping the air inside) and see if the diaphram holds--keeping the air inside the diapghram.   When you take your finger off and let the air escape, you will see if the guts move back.

Also, ensure your vacuum line is connected to a good vacuum.  Make sure your line has no leaks in it....spray WD40 around the line while idling.  If the rpms go up while spraying, you found a leak.

SgtDel  

Edited by: SgtDel at: 1/1/06 2:36 pm

[fxjnkmn]

Just be careful with WD40 spraying, it is flamable, trust me I know, I had it flame up on me once, since then I use soap and water in a spray bottle when I'm checking for vaccum leaks. For a long time I used WD40 and had no probelms, but. Don

[dragmine]

With the engine running pull the vacum hose of and see if idle changes. if it does you have it on a full vacum port and it should be on a timed port. Check your timing with advance hose to carb plugged. Note the amount of timing then take the engine to about 2000 rpm and note timing.Hook up vacum adv. and check again you sould see about a 10'to 20' jump in your timing .