I replace the mechanical advance heavy spring out with a light spring today. I now have a medium and light spring…Maverick runs a whole lot better now. I also figured out why the vacuum advance canister never had any effect when adjusting. I compared the movement to a Duraspark and the Duraspark moves a good 1/4" or better.
yep.. I'd guess bmcdaniel is right about the diaphram being bad in the old one. Just like the old secondary vacuum pots on Holley's.. they crack with age and begin to leak over time. Just keep in mind that there is no max advance limiter in those stockers and that after you speed up the mechanical curve with lighter springs like that.. you'll need to back off the total amount of mechanical advance allowed. A timing light is a must have. Easiest way to do that is to bend the springs mounting tabs to add tension to the spring and keep it from advancing too far when you're at top rpm that the motor will ever see. You can also go light spring in combo with a very heavy one set to have some slack.. which then acts like the limiter once it engages as the light is near fully extended. Or better yet is to braze the advancement slots seat to allow fine tuning. Some folks will make the mistake of backing off initial timing by clocking the disty back to compensate for too much total with lighter springs.. but that is the wrong way to go if you want crisp throttle response and really high idle/off-idle vacuum(which go hand in hand). I usually go as high an initial setting the engine combo will allow(cam and compression make the largest impact here) before hot crank issues creep in to stress the starter too much.. and then go with a more medium'ish weight/spring setup which won't stretch too far and put you way out for a total number. Also best to get an adjustable advance pot if you really want to dial it in for the combo/curve. Some factory pots even have adjustments too so it may be worth checking that one out with an allen wrench. Just be sure to go gentle and feel around for the set screw so you keep from puncturing the diaphram if you get the wrench in really cockeyed. Another tip is to check end clearance for housing/gear. They are often sloppy as hell which results in some spark scatter and slight timing fluctuation as you come in and out of the gas abruptly. Easy way to check for too much slop with the cap off is to just rotate the rotor back and forth to see how much it slides up and down the cam gear. Slight/heavy timing chain slop will also add even more variable to that mess too. Best to use a hardened roll pin when you put it back together too since that will have you tearing your hair out when it shears and jumps out of time. You could also add a thinner pin into the regular one to double up it's thickness too. I can't even count the number of times I've quickly assumed that I popped/bent some valves only to find out(after rolling the motor over to check rotor alignment at TDC) that it just sheared the gears pin.
I replaced my distributor today with a rebuilt unit. I notice when putting the Pertronix back in…the mounting plate was rubbing the vacuum canister arm. Disregarding what the instruction sheet said…I had to do modification to the plate with a bench grinder and file. After a test drive I bent the spring tab toward center to help speed up the advance. I'm still not happy with the out come so I will be changing some springs. Total advance is all in at 3200rpm (70mph)...shooting for around 2200
