Hey guys,
Im running an s4 13b on a 1st gen dizzy with dellorto sidedrafts. I've been tuning and tuning and tuning and I have it running pretty nice. It takes off easy with decent power down low and pulls all the way to redline, however I know its still not quit right. I'm not sure where the dizzy should be sitting for timing? I was told not to use the vacuum advance. Should the timing be left in the factory position that te cas was mounted at putting the leading timing on the front mark on the pulley when using a timing light? I've searched and every one says it should be adjusted but I'm not sure where to? If anyone with a properly tuned carb'd 13b could post a pic of their dizzy timing mark it would be muchly appreciated.I'm trying to get a good street tune till I can pick up a wideband and have it tuned. I don't understand timing degrees so please post a pic. Thanks in advance

 

Most ppl Time to 27 degrees advanced at 4000RPM. Since ur not running vacume, You need to either get ahold of a adjustable timing light or take the front pulley off and mark it every few degrees. There is a few wright ups about that. And most run the vacume advance for low end torque. And u run that on a ported source.

 

one thing I can tell you is be careful of over advancing timing. As I had done this on one of my 12As and I believe this to be the cause of a broken apex seal and destroyed rear rotor housing and rotor. as far as I could tell during the time I was running it set to high I didn't hear any knocking or pinging, that one would expect from a piston engine

 

the dizzy would be set the same as the cas would. with the #1 rotor at TDC, line up the marks on the dizzy and drop it in.

 

Like I said, I'm looking for a nice street tune. How far from the leading notch on the pulley is 27 degrees? Or even 24 degrees? Should I time it with rpm at 4k? Can anyone show me a pic of a dizzy mark at say somewhere between 22-27 degrees? Thanks guys

 

1) Measure outside rim diameter of pulley with piece of string (don't stretch it), then measure that string with ruler.
2) Divide measurement by 360. You now have the distance on the circumference equal to 1 degree.
3) Multiply by number of degrees desired.
4) Measure that distance on pulley & mark.

Done.

Alternate version:

1) Look up in tech manual for your engine model year the difference in standard timing between leading and trailing timing marks. (Example: on 80 12A difference between lead and trail is 20 degrees per FSM, so distance between marks on pulley equals 20 degrees rotation)
2) Measure the distance on the pulley between the two stock marks.
3) Divide measurement by number of degrees. You now have distance per degree.
4) Multiply by desired number of degrees.
5) Measure and mark.

Done.

 

https://www.rx7club.com/1st-generation-specific-1979-1985-18/yet-another-side-draft-question-931901/. The leading timing mark on the stock 6p engine is I believe at 5 degrees after top dead center(atdc). The trailing mark is 10 degrees before top dead center(btdc). Don't quote me on that but for my example those marks are 15 degrees apart from each other. Use a dial caliper to measure the distance and divide it by 3. Measure that distance which is 5 degrees from the leading mark towards the trailing mark, this will give you reference to top dead center. If you multiply 5x4 its 20 degrees. measure that distance from tdc toward the leading mark and it will be at 20 degrees btdc. I would get a wide band o2 sensor on the car to check your afr's before advancing your ignition very far. Engines make best power when the the spark ignites the air/fuel mixture before the rotor has reached tdc, having your timing set at the stock mark on the stock 13b 6p pulley will leave the engine down on power

 

Sorry, 350, but that's not right.

With a caliper, you are measuring a chord (straight line between two points on diameter), not an arc (a distance on the diameter).

A chord from point A to B on a circle is shorter than the distance fom A to B following the diameter. The more degrees crossed by the chord, the larger the error becomes. And a chord of length 4(AB) is not equal in degrees crossed to (AB)+(AB+(AB)+(AB), four similar chords.


If you multiply that chord, then again use calipers to mark it off in one whack, you will induce circular error, equal to IIRC something like 1/2pi times the number of degrees crossed divided into 180.

Measuring the distance on the perimeter is the accurate way to do it, unless you take the pulley off and use a protractor.

Will draw you a diagram if you want to see why.

Granted the difference is small; but on a 100mm circle, the difference between four sequential chords and one chord 4 times the length is noticable.

 

Timing marks on the S4 NA are: Leading: 5* ATDC, Trailing: 20* ATDC. Fortunately for us the timing pulleys for the 1st and 2nd gens have a 360 mm circumference, so on the pulley, 1* of timing is 1mm, simple. Set timing at 24* L. 16* trailing at 4k rpm.

 

A 13B should do better with a split of 10°. Set L to 0° and T to 10°ATDC.

Since this is an S4 pulley, make your new L mark 5mm to the right of your original L mark (when viewed front to back), then 10mm to the left for your new T mark. Verify accuracy by measuring from your new marks to the stock ones to make sure they're within the +/-1 degree width of stock marks, and positioned correctly, before filing (or dremeling like glazedham did) and paint.

 

If trailing is already at 20° then when I adjust the dizzy to get leading up to 24° won't trailing be further advanced? How would I get trailing down to 16°? Later as it gets dark ill use the timing light and see what I can learn

 

With our dizzy designs, we have to always set leading first.

Leading is set with the hold-down nut, trailing is set by adjusting the trailing vacuum advance on it's mount.

Too bad our pulleys are too narrow on the front to use a full-on timing tape. Easy enough to make at 1mm/deg.

 

True about the error, sorry it's been a while since I actually did mine and forgot about that fact. I marked my pulley using the dial caliper from one point to another I subtracted 1/3 of the total distance between the two marks for reference to TDC to equal 10*. Then marked 10*BTDC then measured from that line to reference 20*BTDC. I did realize that they further you move away from the original referance mark by opening the caliper the real distance in degrees would be skewed so i tried to minimize the amount by using the same distance twice instead of lengthening the caliper. Again sorry about the miss information.

 

FYI

The preignition, if you induce it with excessive advance will sound like pop corn popping. At least mine did, and if you ignore it will break the apex seal.

 

i never heard anything, but then again i was running straight through fart can, with no cat, and 2 1/2" pipe, as well as the induction noise from the weber. probably covered it up pretty good. but definitely had it set way to high, it was somewhere around 15 deg BTDC base timing when i finally checked it. i messed with the dizzy setting and then thought i got it set back. i was wrong cause when i finally checked it, i had it way too high and shortly after i had an apex seal in my rear housing go. that seal was totally missing when i tore it down and all the rest were obviously cracked and damaged. needless to say i won't be making that mistake again.

 

So the vacuum ports on the dizzy is for trailing? Racingbeats instructions for installing the dell'ortos said not to use them vacuum advance....? Where should i run those? (The 2 vacuum ports off the lim that stick up right next to each other?). So I didn't make it to use the timing light last night. ill get to it tonight, However earlier retarded the dizzy just a notch and lost quite a bit of low end and gas mileage...I adjusted back after an hour drive (both directions) but I think I may have moved it a hair more advance than it was because it seems to be pulling a lot harder. Its still holding back tho lol. I'm horrible with math by the way so please bare with me. I have to change my brothers car back to fuel injection tonight bc the holley we got with his jaytech manifold is garbage and wont tune ( after we rebuilt it) so after that ill actualy start testing my timing and try to get it right. Thanks for all the advice and help guys. It is muchly appreciated.

 

those vac ports will be one each for leading and trailing. never used a dell so can't be of any help on hooking them up to it.

 

Vacuum diaphragms are one for leading, one for trailing. The trailing one is the one with the adjustible position.

In the below picture, trailing is the one toward the bottom.



From the factory, the trailing diaphragms had a round silver and blue "T" sticker on them, but they can fall off over the years.

 

^80

 

In your original post you mentioned that you know that it is not quite right,

Just exactly what is it doing that is not quite right?

 

When I changed from a cas to the dizzy I had started with the dizzy sitting where the cas used to be. Then I started advancing after a couple of days like I would if I was advancing the cas (adjusting it on the slide nut that holds it on). I know its supposed to be advanced. It isn't making the power it should be until around 6500rpm then jumps to 7000rpm and still wants to go. But if I richen the a/f mixtures any at all it bogs down like crazy as u go to take off, however if I lean it out any at all then it stops pulling around 4500 like it doesn't have enough fuel. Credit I don't have a wideband yet so I'm guesing a/f ratios but either way I adjust the mixtures it has less power. This is a stock port engine so there is no reason to for it to a power band that high in the rpm.

Divindriver, ur saying that adjusting the swing nut is for the vacuum diaphram for trailing? If that's correct then how do you adjust the leading timing?

Again sorry I sound like such a noob here, I have been running fuel injection on my fc since 05 so the dizzy set up seems to be different than I expected lol. Searching never finds all the answers.

 

The leading timing is adjusted via loosening the nut that holds down the dizzy, & rotating the entire dizzy.

When you change leading timing in this way, trailing also shifts - - that's why you MUST establish proper leading timing first.

Once leading timing is set properly, the trailing timing is then adusted by sliding the trailing timing diaphragm inward/outward on the mount, after loosening the hold-down screws.