On tuning my new motor yesterday, I was trying to set the timing. I pulled and capped the vac. advance, and idled the car as low as possible, and the initial timing was about 20 degrees. the way it is tuned now it does not like idling below about 1000-1100 rpm. The problem is that at this speed, it is already advanced to about30 degrees, and that is with no vac. yet. It tops out at about 44 degrees with vac. Could my problem with the low advance speed be the wrong weights and springs in the distributor? Which weights would work best for my application?
I am currently running a Pertonix dist with an msd-6al box, demon 750 speed demon, victor jr, comp 290 xtreme cams, AFR 195 heads.

How much vacuum does it take to actuate your vacuum advance fully?

Do you have the correct timing chain cover with the tab in the correct location for your harmonic balancer?

Sounds like maybe you need to adjust the carb.Or does that pertronix dist have bushings as well as weights to control the amount of mechanical advance.If it has bushings, you may need to put in different ones to limit the amount of advance...

your curve is to fast! your weight and spring combo is wrong at the moment.and it looks like maybe your mechanical advance is going to be more then 16*

at this time do nothing with the vacuum can............leave it alone until you get your base setting(initial) and your total timming set.

right now it sounds like you have to light of springs in there. stiffen them up and get your base setting stable........if you use to light of a spring your timming jumps up and down...causes problems with idle..........

you should be able to idle from about 600 rpms to about 1000 rpms with no advance.( a few degrees would be ok but the less the better) if your motor starts advancing in this range it causes alot of headaches to try and get your car to idle in gear.think about this....with your car in gear at 600 rpms it has 20* and say you put it in park then your idle goes to 1000 rpms and it has 26*............why do you think your idle goes way up? because you gave the engine more timming.........take that extra 6* out and the car will run at 850 rpms........so now you have a 250 rpm drop between park and in gear instead of 400.......and your timming is solid at 20* from 600 to about 1000 rpms.............

so get this part taken care of. once you got that part under control then you can start to take a look at you total timming.......which you may need some bushing to limit your mechanical advance to about 36*.........

once you get this far most of the time the timming curve isnt to bad and it comes in fairly good about 3000 rpms........you can go back and fine tune it but just keep your eye on the timming advance for idle and in park rpms.....so your not messing that up.

after you got your intital timming set...a nice smooth curve that runs from about 1000 rpms to 3000 rpms and have the total timming set say 36*
then you are ready for that vacuum can..........

boy do i have to go thru that one to.....

this is a tunning device it has no value to hp.........this is purely to help the motor get better gas milage , help run cooler at idle or cruising down the highway.

if the engine is way low vacuum most adjustable vacuum cans are no good for the motors.......because it causes i high swing in rpm from park to idle.........the stock unit can work better with lower vacuum motors......but you have to find one with either 10* or 14* or 18* degree mark on them........one that is marked with 10* will allow for 10 more degrees over the idle timming..........

so if yours is set at 20* then with the can hooked up to full vacumm you will have 30* at idle...........with 46* total

in all honesty you should fine the 10* stock can because with 20 initial adding 10 making 30* is more then enough for any motor..and running down the road with 46* isnt bad at all

..some stock cans are rated much higher and these will send a motor like yours into high speed miss.......and end up with your timming in the 50's and higher......

the adjustable units ........they are not bad.........but they dont work worth the crap in a low vacuum motor.........say 5.5" 6.0" at idle.............but if your motor has some good vacuum it should be ok.........get it set to give ya about 10 extra degree and go from there and hook it up to full vacuum so that way when you hit the gas for going fast it is void..........you then will be running off purely your weights and springs.......

is this over yet im done typing.........lets see how many agree and disagree about my ways of doing things........

Ddeennis, the info you provided is exactly what I was looking for, that is what I expected, so to hear it from someone knowledgeable is great. The motor does only make about 5-6 lbs of vac. at idle, so I will look either for a lower adjustable or a stock int the 10 degree range. Thanks everyone for your help, now I just have to find that little bag of weights and springs again and go to town tuning!

Did you ever do any jetting on that carb?

with tuning, especially the carb I bet you'll end up with more than the 5-6 inches of vacume you have now. Get the spark curve dialed in then tune your idle circuit-a vacume guage can be handy for this. You may end up cracking the secondary throttle blades open alittle for more air at idle or drilling .060 holes in the primary blades. These mods are ususally a requirement with cams having alot of overlap/reversion in the intake at idle.

No I have not yet rejetted the carb, the Demon style is not what I am used to, so I am a little scared to start ripping into it. I bought a demon book about tuning, but it is farely advanced, so I have some serious reading to do before I start drilling stuff out, or I will probably drill the wrong thing out!