Moparts
Spark curve
Posted By: RoyceFlo73
Spark curve - 02/08/09 01:53 AM
So i have bought a wysco HEI. Ran it lightly so far and everything was okay, I've been working on the car, i've never really driven it to see how she goes. Until today at least, and its kinda a pig at first, then it wakes up.
I checked my timing, and I have 10degrees btdc with the vacuum plugged. The engine is pulling vacuum at idle, and idling a little high. So when I plug the distributor advance in it jumps 14 degrees. It goes from 10btdc to 24-25. My thoughts are that the idle was too high, and therefore too much vacuum. but i can't drop it any lower without stalling. Its at around 850-900rpm. The carb was entirely cleaned and rebuilt and in tip top shape via Kurt upton from Carbs R us in CT. (good guy to deal with btw.)
Other idea was that i need to adjust the vacuum advane, but there isnt any allen key to adjust it with. It appears that I can remove the pot entirely, but seems kinda stupid to have to do that to change the advance doesn't it.
ANY ideas are welcome.
Posted By: jbc426
Re: Spark curve - 02/08/09 02:43 AM
Are you hooking the vacumn advance to a manifold vacumn source or to the spark port vacumn source?
There are a lot of variables that come into play when determining the best curve to use for a given application, but in general, some would say to skip the vacumn advance, run more initial, less advance and limit your total timing to 38 or less.
It all depends on what your engine/car combination is. More information would help. There are a lot of knowledgable people on this site, but they need more info to help you get started towards sorting this out.
Posted By: RoyceFlo73
Re: Spark curve - 02/08/09 07:19 AM
Its a 73 dart with a stock 273. i am seeking an medium between performance (almost an oxymoron with stock 273) and MPG. I am running the vacuum advance right to the vacuum port in a stromberg carb. I have 10 degrees btdc initial timing, and apparently the vacuum advance pulls the timing an extra 14 degrees btdc. At idle right now, with vacuum advanced attached and all my timing is 24 degrees btdc at idle.
With the vacuum advanced plugged into the carb I'd have expected maybe 14 degrees btdc. But given that the vacuum advance should only give an extra 14 degrees advanced at WOT (from what I understand) it appears that I am pulling to much vacuum or that the vacuum advance isn't tuned right.
I am just wondering if anyone has had any similar problems and what they did.
Posted By: RapidRobert
Re: Spark curve - 02/08/09 12:08 PM
Why is the idle speed so high? Wild cam? The vac adv amount is OK. You want your initial ~10 btdc with or without vac adv(whichever your eng/cam runs best with). You need enough(initial) adv so it will idle right with that cam but yet not go over 35(checked w vac adv disconnected) & since you have had it at 10 & it ran I'd put it back there & work on lowering your idle speed & each time resetting your initial to 10. 24 initial is way too much
Posted By: Dodgem
Re: Spark curve - 02/08/09 03:43 PM
If your vacuum advance is affecting idle it's on the wrong port.
recurve the distributor and using the many time posted method to power tune your engine then the vacuum advance which should only work a light cruising conditions and in MHO has no place on a performance engine!
Try moving the vac advance to the ported port, rather than full manifold vacuum. My truck was just like you describe, stuttery from a stop, then woke up. Once I went to ported vacuum (and reset timing, etc), it was great off the line.
-Dave
Posted By: RoyceFlo73
Re: Spark curve - 02/08/09 10:50 PM
My vacuum advanced is attached to the nipple on the back side of the carburetor (stromberg WW). I don't see any other option to plug into. I think im missing something here.
Posted By: Dodgem
Re: Spark curve - 02/11/09 06:49 AM
Is it like this??
(68 273/318)
Posted By: RoyceFlo73
Re: Spark curve - 02/11/09 07:27 AM
No, I wish it were a BBD. I have a stromberg WW. Have no idea how that found its way onto the motor, i thought all were stock with BBDs and i bought the engine from a guy who did nothing but restorations, seems like a carb is an obvious thing to get wrong in an all original resto.
Anyways, I'm pretty sure i have the vacuum advance in the right spot. I have a stromberg WW. The vacuum advance is plugged into a port on the back of the carb right above where the PCV is plugged into. The V.A. port is not below the throttle plate, its half way up.
My ideas from here are to frig with the mixture as much as possible to allow the idle to drop until I don't get any vacuum from that port. As of right now, if i unscrew the idle screw any more, the engine wants to stall. So i figure I'll lean it a little bit and keep dropping it. I have to get a vacuum gauge maybe, that could probably help get best mixture. Then, i'll play around with the timing until i can get it right.
I set the intitial (with V.A. plugged) at 10btdc. With the V.A. to the carb i shouldnt see any more than 14btdc right?(at idle).
Because right now I have 24btdc once i attach the V.A.
Posted By: Dodgem
Re: Spark curve - 02/11/09 03:57 PM
All my Chysler books show the BBD but I'm not sure the strom is different a lot of searches showed them as the same???? Some carbs were marine and maybe even some military have no ported vacuum for advance as they don't use it!!!!
Anyway plug that vacuum port for now. Now start advancing distributor till you get a light ping under acceleration. probably around 34 to 35 deg total mechanical and initial. reset your idle and see if the vacuum is gone from that port.
real initial is set not running. i think you are giving me idle advance which is initual and some mechanical in??
Posted By: Dodgem
Re: Spark curve - 02/12/09 12:32 AM
Of course if you advance with vacuum plugged till light ping back up till it goes away and lock distributor. Then making sure if it has two idle mixture screws you equalize them. 1.5 turn both or 2 turns 1 turn both and so on.
Posted By: RoyceFlo73
Re: Spark curve - 02/12/09 12:49 AM
I advanced the timing to about 14btdc. I adjusted mixture screws and got it to idle low, i still have some vacuum at idle, but not a lot. When I plug the V.A. in i adjusted it where i have a few degrees of advance, but it seems to run a little better.
The WW is close to a carter BBD, slightly different. I will make due with this setup for a little while. I have a M1 manifold, TQ, and 340 cam that is going in next month when its a little warmer to work on it. I'm gonna get a new distributor too, this wysco kinda sucks. When playing with it today, i noticed the cap doesn't even stay clamped down perfectly, it shifts a little. Plus, i can't get any tech help from them, they refer me to dealers and such, who help as much as they can but can't seem to answer all my questions. I'll get my old points back in with the petronix Electric ignition.
RIght now, it drives. It's slow, but then again everyone said the 273 would be. Especially since i think i only have 2.94s or something like that for the rear end. The engine seems to wanna work to rev up, as soon as i find some leaf springs i want i am going to fix up the rear end with 3.55s as well.
As it is now, from a dead stop if i snot it, i can get the tires to spin for about 20-30 feet. Yet, if i'm even slighly moving at maybe 5mph or so and snot it, it won't spin em, it'll kinda just plod along.
Posted By: Dodgem
Re: Spark curve - 02/12/09 02:18 AM
I'd try 18 deg but your on the right track then adjust everything before hooking up the vacuum.
Short test drive reset idle and try vacuum again.
Posted By: RoyceFlo73
Re: Spark curve - 02/12/09 02:34 AM
Thanks a lot man, you've been a big help. Sometimes its hard to tell if your coming or going when doing this.
Posted By: GTX MATT
Re: Spark curve - 02/12/09 02:40 AM
Quote:
I advanced the timing to about 14btdc. I adjusted mixture screws and got it to idle low, i still have some vacuum at idle, but not a lot. When I plug the V.A. in i adjusted it where i have a few degrees of advance, but it seems to run a little better.
The WW is close to a carter BBD, slightly different. I will make due with this setup for a little while. I have a M1 manifold, TQ, and 340 cam that is going in next month when its a little warmer to work on it. I'm gonna get a new distributor too, this wysco kinda sucks. When playing with it today, i noticed the cap doesn't even stay clamped down perfectly, it shifts a little. Plus, i can't get any tech help from them, they refer me to dealers and such, who help as much as they can but can't seem to answer all my questions. I'll get my old points back in with the petronix Electric ignition.
RIght now, it drives. It's slow, but then again everyone said the 273 would be. Especially since i think i only have 2.94s or something like that for the rear end. The engine seems to wanna work to rev up, as soon as i find some leaf springs i want i am going to fix up the rear end with 3.55s as well.
As it is now, from a dead stop if i snot it, i can get the tires to spin for about 20-30 feet. Yet, if i'm even slighly moving at maybe 5mph or so and snot it, it won't spin em, it'll kinda just plod along.
Thats how my 273 is. Where in CT are you? Ive got a 340 cam in mine as well.
Posted By: RoyceFlo73
Re: Spark curve - 02/12/09 03:31 AM
I am in southington, about 15 minutes south of Hartford.
I'll be caming the motor and doing everything else to it this coming march, when its a little warmer.
Posted By: Dodgem
Re: Spark curve - 02/12/09 01:08 PM
Then you have to start all over! LOL!
Probably need a lighter spring kit for whatever distributor you use?
Posted By: RoyceFlo73
Re: Spark curve - 02/12/09 07:15 PM
Haha, I don't think so, I'm getting a MSD or something else. I really can't stand this one...
Posted By: Dodgem
Re: Spark curve - 02/13/09 02:25 AM
Well i definatly find advance springs in MSD to stiff otherwise good distributors!
Posted By: Magnum
Re: Spark curve - 02/13/09 05:43 AM
Quote:
its kinda a pig at first, then it wakes up.
Which vacuum port is connected has nothing to do with your power problem. Either port will have ZERO vacuum at wide open throttle so save the port vs manifold vacuum for another thread. Oh, we did that 100 times.
How much of a pig is it? It's a 273, that's pretty much how they are until you spin them a bit.
Do not remove the vacuum pot completely. If you chose not to run it, just leave it disconnected.
Report back with your total timing and what rpm it comes in at. Also need more info on the engine and drivetrain.
I would try more initial timing. Whatever your starter will handle is probably barely enough.
Posted By: RoyceFlo73
Re: Spark curve - 02/13/09 06:58 AM
I have 15 btdc initial. It's plugged into ported vacuum (above the throttle plate)
This stupid vacuum pot when plugged in was pulling 10, so a total at idle of 25 btdc. Backed off the pots timing with the allen head adjuster, got it to about 20 btdc at idle with the vacuum pot in.
I haven't messed with any mechanical advance because, these guys at Wysco don't wanna talk to me at all. They send me to their dealers, who don't seem to care now that I already paid for the damn thing. So i don't know where to get weights/springs for it.
Its a 73 dart, a stock 1967 273, 904 trans, on 2.96 gears. Dual exhaust, no power brakes.
When i had my /6, which had a carter BBD, i idled the thing down until my ported vacuum didn't pull any vacuum. Then i set my initial timing, when i pluged my V.A. in, my timing didn't change at all. It wasn't until I was at partial throttle.
Posted By: Magnum
Re: Spark curve - 02/13/09 01:46 PM
Two things odd about your results.
The 3/32 hex key in the vacuum pot should only adjust the amount of vacuum it takes to move the pot. The number of degree it moves with vacuum, compared to without vacuum is a fixed into a stop on the arm. Not adjustable (unless you modify it).
If you are using ported. You should not have vacuum at idle. So your timing should not change at idle with or without the connection plugged in at idle.
15 initial is pretty good. A 2.96 geared 273 is not going to do too much off the line.
Switching the vacuum connection to manifold vacuum will give you a slight increase in torque at partial throttle because you will have more timing but deep throttle will be the same.
Posted By: RapidRobert
Re: Spark curve - 02/13/09 01:53 PM
15 initial(checked with vac plugged) sounds good, ported(in this case) vac adv sounds good, If your total is 35(or close to it) checked w vac plugged you're good. I think if you could get your idle speed down to where you have no vac(to the vac adv) that would fix most of this issue. The mechanical curve(springs/slot length) & the vac pot amt of adv could fine tuned later. I think you need to get those throttle plates closed further rather than backing off the amt of vac adv.
Posted By: RoyceFlo73
Re: Spark curve - 02/13/09 08:33 PM
Yea i think you're right about closing the throttle plates.
In regards to the vacuum pot, when i adjusted the diaphram via allen key, i think thought it made it where more vacuum was required, since the vacuum rate at idle has been constant, that would change how much advance right?
I think part of my issue, is the weather has been going from like 20-55 degrees within a day and it makes it almost impossible to get the air/fuel mixture set to adjust idle.
Posted By: RapidRobert
Re: Spark curve - 02/14/09 12:29 AM
Quote:
In regards to the vacuum pot, when i adjusted the diaphram via allen key, i think thought it made it where more vacuum was required, since the vacuum rate at idle has been constant, that would change how much advance right?
correct
Posted By: dgc333
Re: Spark curve - 02/14/09 01:14 PM
Adjusting the allen key in the vacuum pot changes the preload on the spring that wants to force the arm back to the zero advance position.
Once the vacuum level is above the preload the rate (degrees per "Hg) remains the same.
So, increasing the preload will increase the amount of vacuum required to get the advance to start moving and ultimately the amount of vacuum required to get full stroke from the pot.