distributor vac advance-HELP!!!

[JOHN G]

i have a duraspark 2 with gm module. at idle, the vac advance is in full advance position-this can't be right, can it?the vac advance unit has no adjustment that i can see so can i limit the amount of vac going to it with a valve of some sort? Also, does anyone know what the base timing is supposed to be with the cam i've got?12 degrees is stock-so is it more advance or less with the bigger bumpstick?

 

[Anonymous]

Full vacuum advance at idle is normal assuming you have the vacuum source connected to a manifold vacuum source. At idle is when you have maximum vacuum, therefore maximum advance. At idle, you have little to no centrifugal advance contributing to the total ignition advance. If the engine is pinging etc, then you might try to connect the vacuum advance to a ported vacuum source on the carb.

If the vacuum motor on the distributor has a straight nipple, it may be adjustable. Try sticking a small hex key wrench inside the nipple. There is often an adjustable screw that adjust the tension on the diaphram.

Typically a bigger bumpstick will allow you to run additional ignition advance (assuming the pistons and the stock compression ratio were not changed). The bigger bumpsticks usually have more overlap, which reduces dynamic compression ratio.

 

[JOHN G]

OKAY, THE VAC IS BEING DERIVED FROM THE CARB ALREADY-DOES THE BASE TIMING GET SET WITH THE VAC LINE PLUGGED THEN AS MOST CARS WOULD OR AM I MISSING SOMETHING HERE? SO THE STORIES OF PEOPLE RUNNING 15 DEGREES OF BASE TIMING SHOULD BE TRUE?I DO HAVE A MINIMAL AMOUNT TAKEN OFF THE HEAD AND DECK-DON'T REMEMBER HOW MUCH THOUGH.IT SEEMS THAT WHEN I ADVANCE THE TIMING INTO THE 12 DEGREE AREA, THE ENGINE DOES NOT WANT TO IDLE IN GEAR-I DO THINK THAT I HAVE TO RE-JET THE CENTER CARB THOUGH AS IT IS PROBABLY RUNNIN LEAN.

 

[addo]

Yes, base timing is set with the vacuum disconnected and plugged, and the car in "P" (if auto), electricals switched on to create alternator loading on the motor.

Regards, Adam.

 

[JOHN G]

DID THAT AND CAR RUNS GOOD AT IDLE-UNDER LIGHT ACCEL,STUMBLES-OPEN IT UP AND IT RUNS GOOD, BUT NOT ALL THERE YET. AM STILL BEING TOLD THAT DISTRIBUTOR IS NOT CAPABLE OF ADVANCING FAR ENOUGH FOR THIS APPLICATION.

 

[Anonymous]

I see your running triple Webbers on an Offy intake. Do you have a vacuum gage? If so what readings do you get on the ported vacuum source verses the manifold vacuum source? go with the higest vacuum reading you have. If you don't have enough vacuum to pull the advance you may need to either adjust the tension on the diaphragm (as described above) or recurve the dizzy with softer springs. This was covered in another post recently, I'll see if I can find the link. It had some great information on recurving the DS II yourself.

EDIT Her's the web-site for recurving the DS II:
http://www.reincarnation-automotive.com ... index.html
I couldn't find the post, maybe someone else will referance it for you.

 

[JOHN G]

THANKS FOR THE LINK-LOOKS LIKE IT MIGHT BE THE SOLUTION.I ACTUALLY HAVE NO PROBLEM PULLING THE ADVANCE OPEN AT IDLE IN GEAR-THE MAJOR PROBLEM IS THE CAR STUMBLES UNTIL I BUILD SOME RPM AND OPEN IT UP. AT THIS POINT, THE CAR RUNS WELL, BUT DOESN'T SEEM TO HAVE THE POWER THAT EVERYONE SAYS IT SHOULD. CLIFFORD IS INSISTENT THAT THE DS II CANNOT ADVANCE ENOUGH TO PERFORM TO IT'S PEAK, YET I SEE PEOPLE RUNNIN THEM WITH VERY GOOD RESULTS. EVERYONE ON THE FORUM SAYS I CAN MAKE THIS HAPPEN AND I TEND TO BELIEVE THE MAJORITY!

 

[addo]

Tweaking a distributor is not that hard. Here, amateur racers have done this for years. I would venture a guess your circle trackers may have, too. Most common mods are changing advance limit slots. Either the start of your advance limit slot is TIG-welded up and the finish extended, or the finish alone can be extended. The effect is different to spring swaps, and may be considered complimentary to the practice.

The DS-II is a pretty simple unit. Don't be afraid to pull it apart and start modding. Braze probably works as well (as TIG) if you have a good eye and small torch tip. You should be able to get performance all but equal (at realistic small six operation speeds) to an MSD, out of a properly modded DS.

 

[Anonymous]

i pulled the cap off my distributer to actually look for the springs...i didnt see any, do i need to unscrew a few things to expose the springs? what kind of recurve is good for the distributer? or is it just the vac advance that your talking about?

 

[Anonymous]

i pulled the cap off my distributer to actually look for the springs...i didnt see any, do i need to unscrew a few things to expose the springs? what kind of recurve is good for the distributer? or is it just the vac advance that your talking about?

Go to the web page posted above. The springs are under the breaker plate and shown in step 4.

 

[JOHN G]

TALKED TO THE GUYS THAT MADE THAT WEB SITE-THE MATERIAL ON THAT SITE IS MORE SUITED TO A DS II FOR A V-8. THEY DID HOWEVER SAY THAT THEY CAN RECURVE THE L6 PIECE, BUT IT REQUIRES SOME TRIAL AND ERROR AND TUNING ON THEIR MACHINE.