Hi everyone, New Bee here, my 1st post.  I've read a few of the post here and it looks like someone could answer this for me.  I posted this over on the Dime Quarterly yesterday with no reply yet.  Below I am refering to some info that Jason Gray had posted over on the Dime Quarterly.  Thanks inadvance for the replys....  sorry for the long post,    Randy

I've installed the EI Dizzy and recurved the mechanical advance but am having trouble recurving the vacuum advance. I couldn't have done what I've done with out Jason Gray's article in our Technical Dept. pages. But if Jason is reading this, or if there someone else that knows, when I remove the putty for the end of the vacuum adv canister and turn the outer adj screw counter clockwise to loosen the preload spring on the diaphragm, it still seems to have tooo much preload even with the adj screw all of the way out (literally). Not to be confused with the inter screw for limiting the travel. I'm not concerned about that right now(later). Looking in Jason's list of EI Dizzy's it shows that there are some vacuum adv that function with as little as 2.8" of vacuum to start, that would be great. Question, is this because it is a totally different canister from the factory that if torn down could be adj even to something less than the 2.8" of vacuum to work. In Jason's article it is stated that all of the canisters are the same just set differently from the factory for each application. I've tried this on 2 of my canisters. Any help. Thanks in advance....

Hi Randy, this is Randy, also.

I would like to recurve/reset when and how much the vacumn advance works.  Running a mild cam on my L20, I have a little less vacumn and the advance just barly does start to work.  Vacumn leaks other places mayby, shafts on the SS carbs, intake manifold, I don't know.  I should by a vacuum gage so that I could tell what vacuum that I am pulling.  But in any case I would like to able to adj it to start functioning with no more than 2" to3"and then adj how much at full once it get it to, start it's advance when it should.I thought that recurving/resetting the vacumn advance to start working at my lower vacumn would be in order . Not to adj it all the time, just to set it up for my needs.  Sorry I didn't make myself clear.  Does this help?  Thanks for the reply.       Randy

woops sorry bout that .......

Randy, I reread your post and now see that you were asking why even run a vacuum adv.  Try to bare with me.   It's my under standing that there is no preformance gains for street, from not running a vacuum adv, just less trouble.  With it, better fuel milage and throttle responce, ie low in power.  It's my daily driver.   My L20 I've punched  60 over and running 1st over 280 pistions with a ported U67, duel side ss's, header, cam and springs, just for some back ground.  I'm basicly running with no adv right now also.  I've got the mechanical set at 35 apx degrees full at apx 2900 RPM.  But I sure would like to play with the vac adv. but can't because of the above.   Boy, I should wait and type this at home, alot less type o's,,  Dang aint it a drag when work gets in the way of 510 stuff ???..........

Hi Pakal,  Talking to ya over here also, that's cool.  Like you said this is a very good 510 site.  By the way what engine/cam/carbs and vacuum are you pulling/running, that you still have enough vacuum to move a stock canister at the time that you need?  Below is what I'm trying to do.... hope that this is not tooo much info.

Vacuum Advance

  You should have a functional vacuum advance canister for street driving. The vacuum advance canister alters the ignition timing in response to engine load. The vacuum canister does not produce advance under full throttle operation, manifold vacuum is much too low so canister shouldt effect tendancy for engine to ping under full load.. Under partial throttle operation, on the intake stroke the piston pulls against the blockage of the throttle plate so vacuum is produced in the intake manifold and the cylinder receives less than a full charge of air/fuel and retains more of the burnt exhaust gas in the cylinder. This causes the fresh (partial) intake charge to burn slower when ignited so earlier ignition is needed to extract maximum energy from the fuel. Not using vacuum advance will give you no real increase in performance and will decrease your gas milage and increase emmisions unnecessarily for street driving. The vacuum advance canisters can also be recurved. All the EI dizzys use the same canister that is adjusted at the factory for desired advance characteristics. To re-adjust, remove the putty blob on the end of the canister with a high speed grinder to expose the adjustment screws. Inner coaxial pin limits vacuum advance travel, outer grub screw adjust the spring pre-load on the diaphragm. Turning the outer screw counterclokwise reduces the amount of vacuum necessay to initiate advance. If you are using sidedraft carbs and the vacuum signal is decreased, use a gauge to measure vacuum under cruise conditions and then re-set the advance canister to give full advance at this vacuum level. It may take some trial and error to find the correct amount of vacuum advance, I would think that between 15-20 degrees (crank) at 10-15 in Hg would be a good starting place. Advance beyond the initial + mechanical limit of 36 degrees is needed with under high manifold vacuum (low engine load). For each 1mm of travel of the vacuum canister actuating rod, the timing is changed by 4.24 crankshaft degrees. Once you have finished adjusting canister, you must re-seal the threads of the adjusment screws with paint or hardeing silicon putty or air will leak past the threads.

Above picture shows a vacuum advance canister with the travel adjusment pin and spring preload screw removed. If you need to order a new canister, they cost approximatly $25 new from nissan. Part number 22301-7901 as speced for a 280zx dizzy.

Want another opinion on dizzy recurving? click color=#0000ff here. (chevy info but good).

One of the best things you can do is have some one recurve your dizzy!!!! If you go to a local dizzy shop they will ask things like which size tire what gear and rpm range and block size. All those things go into your curve so just don't leave it at 32 , take it to a shop and at least they can give you some numbers to work with. A buddy of mine did it to his 510 with a lz22 and said it was a huge gain of power and when it can in!! I am goin that route, some things should be left to the pro's. Chris