Basic tuning - timing and carb settings

Dave-R · Post by **Dave-R** » Mon May 30, 11 3:42 pm

If you read my instructions carefully I mention how to reduce the amount of timing in the distributor.

18 degrees is probably going to be pretty ballpark for a fairly stock or mild small block to be honest. So you just need to limit the total timing to suit and you should be good to go.

You know you have enough initial when you adjust the idle mixture to max manifold vacuum and your exhaust does not smell rich any more.

Anonymous · Post by **Anonymous** » Mon May 30, 11 4:49 pm

thanx Dave, mine is a 470 Stroker (400) with a 600 lift cam, the msd dizzy has a advance of 17deg min, had car on dyno and the guy turned the initial right down low to get the total advance, this resulted i believe in low hp figures and a smelly setup, reading your instructions again it seems that the more advance on the initial with as low as possible on the mechanical advance is wots best , ta Al

Dave-R · Post by **Dave-R** » Mon May 30, 11 7:21 pm

Oh then you are looking at probably 25 initial and 35 total for your combo so you only need 10 degrees in the dizzy.

Of indeed you might be able to just lock it out at 34 degrees. But check it will start OK at that without killing the starter motor.

yabadaba · Post by **yabadaba** » Mon Mar 12, 12 6:30 pm

Okay, I know this thread is one I started ages ago, but having just fitted a Mopar Electronic Ignition kit with the orange box I've now got a renewed interest in getting the timing right.

By the time I'd finished fitting it all yesterday it was getting dark so I just set the initial advance at 12° without checking what it was at a higher RPM's and went for a quick test drive. Felt noticeably nippier especially when accelerating from a standstill or slow speeds. This afternoon I tried increasing the initial to 16° and then checked the total advance (seemed to reach that at about 2200 rpm) and it was pretty much bang on 30°. Took it for a test drive and it felt great...definitely more responsive and no pinging (pinking?) that I could notice.

So, am I right in thinking that I should now try increasing the initial to 20°, which should give a total advance of 34°?

Also, these readings were taken with the vacuum advance disconnected and plugged, so as I get near the max recommended total advance will reconnecting the vacuum pipe not Bananarama! too far?

Final question, does bumping up the timing have any affect on the mixture? I've never messed with that before, but I guess I'll need to check it after I've finished tweaking the timing?

Dave999 · Post by **Dave999** » Mon Mar 19, 12 10:15 am

i'd just set it to 34 and see how it goes

go back and chack initial with the vaccum off and plugged after you've done yer test drive.

if 34 at 2500+ brings in too much initial...which it probably won't
the motor will kickback when you try to start it

unless you are going all out with modificatiosn to the dizzy to limit max machanical advance there is not a lot else you can do....

Dave

yabadaba · Post by **yabadaba** » Mon Mar 19, 12 9:26 pm

Thanks for the advice...now sorted I think.

I've ended up with 17° initial, giving 34° total and that is reached at nearer 3000 rpm (not around 2.2k as I had thought earlier). With the vacuum attached it bumps it up to about 52-54° total. The car drives great...no kick-back on the starter and no pinking. Could be me, but I did seem to need to crank it longer than before when starting it from hot.

Getting that extra oomph has now made me think maybe I should go for a new manifold and 4bbl carb....or is that starting to lead down a dangerous road

John · Post by **John** » Mon Mar 19, 12 9:35 pm

52 -54 Total

WOW

yabadaba · Post by **yabadaba** » Mon Mar 19, 12 10:05 pm

JohnS wrote:52 -54 Total WOW

That was measured with the vacuum plugged back in and at about 3k rpm. Was 34° with the hose disconnected and plugged and I think that is how most total advance figures are quoted. Drives great, so I guess it must be okay.

Adrian Worman · Post by **Adrian Worman** » Mon Mar 19, 12 11:24 pm

Pretty good figures, the port is only giving all that extra advance at low load high vac like idle, light part throttle and overrun, WOT and heavy part throttle are giving very low vac. The motor will burn very clean

Get that four barrel on there and enjoy the extra power.......... and fuel bills

db · Post by db » Thu Mar 22, 12 9:17 pm

If anyone can find Dave's original posts on timing and carb set-up can it be stickied please?
Or can Dave please come to my house for a week?

Dave-R · Post by **Dave-R** » Thu Mar 22, 12 9:49 pm

Not sure if you have to register to see these. I think I decided you have to for most of my forums. I can't remember now as it was before i was ill.

http://challenger.mpoli.fi/board/viewto ... 7b69578fe7

http://challenger.mpoli.fi/board/viewto ... f=13&t=828

To find a good initial timing setting these days I just turn the distributor advanced with the engine at idle and feel for when the engine rpm rise is just leveling off. Then check the engine still starts OK. Then use a timing light to see what initial I have. Then I deduct enough timing from the dizzy to give me that initial with 35 degrees total all in by 3000rpm. I check the timing at 2000rpm and change the springs to get half the timing in by then so I get a fairly linear timing "curve" from idle to 3000rpm.

If you want to get fancy you would have to push the timing up at every 500rpm increment to see how much timing the engine will take at each rpm step. That is the only way to get the "perfect" timing curve.

db · Post by db » Thu Mar 22, 12 10:08 pm

I can see those links fine thanks Dave.
Got 'em bookmarked for future reference