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  • beekiller
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  • Krew Krawlers, Mountain Division
How to defeat vacuum advance and upgrade the mechanical
First, I cannot take credit at all for this idea.   It came from several posts by dwrlhc who suggested this as a good way to deal with the vacuum advance issues related to performing motorcycle carb swaps.  Dude, I hope you don't mind!   ;)  I'm simply giving it a whirl here, happened to take some pix, and hope to learn more.  dwrlhc, if you have anything to add please do so.   8)


This mod will allow more ignition advance from the mechanical adv. to offset and eliminate the vacuum adv.  It also allows for faster adv. at lower RPMs.


Begin with the dizzy out, cap and rotor removed.  Carefully peel off the cap gasket.






Remove these two screws so you can remove Exhibit A.  It will still be attached by two wires but there is enough to lay it outside the housing so you can work in the meantime.





Remove the C-clip from the vacuum advance arm.  Using a small screwdriver while holding one finger on the other side is not only easy, but helps alleviate eye damage from flying clips.   ;)






Take out the screw holding the vac. advance can.  Next you can gently pry up on the arm and give the can a twist so the arm clears the nipple.  The can will now pull straight out of the dizzy.





Remove the two screws which hold down the pickup plate.  Leave the pickup on the plate as this requires adjustment if it is loosened.  






Note the location of the slots where the plate clips go.  When you reassemble it is important the clips line up with these slots.  Gently wiggle the plate to get it out of the dizzy.  Also, make sure the clips don't come off the plate.  If that happens, a hundred little balls will spill out of the bottom.   :o






This is the area you want to grind to gain more mechanical advance.  This demonstrates trimming if needed.  Read this post before trimming:

Clicky here

Clean out metal shavings.






These are the springs to be replaced.  Here is one suggestion for replacement springs:   Click here for more info








Reassembly is mainly reverse of disassembly.  Remember to line the plate clips back up with the slots in the housing.  The plate has the ability to spin, hence the ball bearings.  This is how the vac. adv. worked before.  I replaced the vac. can for a couple of reasons.  One, it clocks the plate back where it should go.  Two, it prevents the plate from possibly turning in the dizzy which would throw off timing.  Just leave it unhooked and plug the other end of the vac. source.  

I'm still playing around with initial timing, but it does advance quick now!!   :)  This mod took about 1.5 hours from dizzy removal back to running truck.   ;)
  • Last Edit: Thursday, Jun 02, 2016, 09:58 PM by beekiller
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  • samurota
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  • Krew Krawlers
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #1
 What did total advance end up being?
I have done Ford distributors The have a stem with different limiters and each Dist stem has 2 limiters built on it. I had a 351 that liked a lot of timing and I think I had 42 degrees of total advance. It had  a 21 degree mechanical advance with a 8 degree vacuum advance

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #2


What did total advance end up being?




That I do not know.  I don't have one of those "good" lights.   :-[  I'm shooting for mid 30s.
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • X-jeeper
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #3
i would love to do this but i have a hard enough time with the distributor as it is haha
Irish people dont say "have a nice day" we say "GOOD LUCK!"

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #4


How much of a difference does it make? Any significant change in performance? Thanks.




Decent drivability improvement (so far, just did this last night and drove it to work this morning).  But that's with a Harley carb.  The stock carb has a ported vac. for the timing adv. whereas the Harley carb doesn't.  I don't know how much it would help a stocker.   :D
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • ZukiJon
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #5


Decent drivability improvement (so far, just did this last night and drove it to work this morning).  But that's with a Harley carb.  The stock carb has a ported vac. for the timing adv. whereas the Harley carb doesn't.  I don't know how much it would help a stocker.   :D


It won't be on a stocker....Why new springs? I've got everything done but springs, guess I gotta go pick some up. Got a part # for them or does it matter. Thanks.

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #6


It won't be on a stocker....Why new springs? I've got everything done but springs, guess I gotta go pick some up. Got a part # for them or does it matter. Thanks.




Gotcha.   ;)  The new springs (small block Chevy) are a lighter spring, which allows for faster timing advance.  The stock Zuk ones are waaayyy stiff.  Probably never get all the advance from them.   :)  Nah, I was lucky and walked into a parts store with a guy at the counter who managed not to slobber on himself without the computer.  He went in the back and came back with a pair of SBC springs.   :D
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • ZukiJon
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #7


Gotcha.   ;)  The new springs (small block Chevy) are a lighter spring, which allows for faster timing advance.  The stock Zuk ones are waaayyy stiff.  Probably never get all the advance from them.   :)  Nah, I was lucky and walked into a parts store with a guy at the counter who managed not to slobber on himself without the computer.  He went in the back and came back with a pair of SBC springs.   :D


Thanks man.




Oh, and the Hitachi will be used....just not with this project.....thanks. I've got two down in the driveway with carb issues. One I think might be because of the vac. advance not working right as well as some tuning issues. We'll see.......

Re: How to defeat vacuum advance and upgrade the mechanical
Reply #8
i got a 32 36 webber on my 1.3 zuks would i feel or should i say noticed the diffrance  in performance?
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  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #9


i got a 32 36 webber on my 1.3 zuks would i feel or should i say noticed the diffrance  in performance?





You may gain a little.  I wouldn't say it's huge at all, but it does help.  This is really targeting the use of the Harley carb, but I don't see where it would hurt to do this with a Weber.  You might PM Sarge and get his thoughts on it.   ;)
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • kelcrist
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #10
i did this mod today in about 30 mins  thanks mostly in part to the nice tutorial here.      i dont know if i feel a real difference but i run the mikuni carbs and now i know i am at least getting some advance.        

  • ScotY
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #11
Are these the Chevy springs to use?
http://www.summitracing.com/parts/MRG-928G/

Any chance anyone knows a part number I can give the guy at the parts store to look up?  Or is this something you probably can't find at Napa?

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #12


Are these the Chevy springs to use?
http://www.summitracing.com/parts/MRG-928G/

Any chance anyone knows a part number I can give the guy at the parts store to look up?  Or is this something you probably can't find at Napa?



Can't see any problem using them.  Since that pack has three pairs of springs, each pair at a different advance rate, remember you can mix and match to achieve the advance curve you want.  For instance, ya could use a silver one and a gold one, or whatever gives you the advance you want.   ;)
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • Bigrob26
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #13
would this work on a stock 1.6 TBI?? im not getting enough advance mostly because its dirty in the dizzy, but would the modifying work for EFI??
-bobby

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #14
With TBI I believe you're now talking all computer control.  Someone correct me if this is wrong, but I don't think the 1.6 dizzy has mech. adv.   :-\\\\
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • Bigrob26
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #15
i know it has vac. advance, and i beleive mech. too because many people do the gsxr swap and few of the setups ive seen have conected the vac. advance, they just unplug and rely on the mechanical..
maybe im wrong...
-bobby

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #16

i know it has vac. advance, and i beleive mech. too because many people do the gsxr swap and few of the setups ive seen have conected the vac. advance, they just unplug and rely on the mechanical..
maybe im wrong...



Yeah, and that's the point for doing this mod.  But most who have done a 1.6 swap still use a 1.3 dizzy.   ;)

Just looked at a 1.6 dizzy I happen to have.  It does NOT have a mech adv.   :)
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.

  • Surly
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #17

i know it has vac. advance, and i beleive mech. too because many people do the gsxr swap and few of the setups ive seen have conected the vac. advance, they just unplug and rely on the mechanical..
maybe im wrong...


I'm pretty sure that only the 1989 Sidekick/Tracker 1.6 EFI distributors had vacuum advance mechanisms. 1990 may have been a crossover year, but this mod would NOT be appropriate for EFI distributors without vacuum advance.

  • Bigrob26
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Re: How to defeat vacuum advance and upgrade the mechanical
Reply #18
i have a 1990 so ill just have to tear it apart and find out
-bobby

  • beekiller
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  • Krew Krawlers, Mountain Division
Re: How to defeat vacuum advance and upgrade the mechanical
Reply #19
It just dawned on me what Surly is referring to.  The early models had a carb.  The point being if your's is EFI there won't be a mech adv, but if it's carbed go for it.   8)
All I want from tomorrow is to get it better than today.

Claiming you are offended is essentially saying you are incapable of controlling and managing your emotions, so everyone else should do it for you.