Fuel and ignition revamping (solved?)

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MomsDuster

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Did a complete revamping of my fuel and ignition system. Went from a FiTech FI with timing control to an 800cfm Edelbrock ASV2 w/ a MSD streetfire ignition box and a MSD pro billet distributor. So for the particulars:
71 Duster
440 according to the builder 10:1 cr
Comp cams XE275HL with 1.6 rockers
727 2200 stall
3.73 gears
I initially set a base timing of 18* with the 18* bushing and heavy silver and light silver springs. 900 ish rpm at idle in park and 800 in drive. I also put the lightest metering springs in the carb. The car runs well but when the fans come on at idle in gear it just sounds like it’s off a bit. The Rpms fluctuate and just doesn’t sound right to me. It doesn’t flood or die just again doesn’t sound/feel right. I’ve tried to add some advance and that helps, but then my total timing gets way up there and that kinda scares me. I’m pretty new to this tuning thing so any tips, tricks, advice would be appreciated. Cam card attached. I’m sure the gurus here will have plenty of questions and comments and I wii try to answer to the best of my ability. Thanks folks.

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A vacuum advance distributor is in order to correct the street manners. Pro billet distributors are great for racing, but a vacuum advance is hard to live without on the street unless your driving something a whole lot wilder than your build. We need to know which head and what spark plugs you are running, too. If you want to do this simply and effectively as possible, talk to FBBO ignition and order one of their systems. Tell them your combination and they will tell you exactly where to set your advance curve and how much total and static timing you need.
 
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Love that car, BTW. Makes me want to start building a 451 to drop into mine.
 
I initially set a base timing of 18* with the 18* bushing and heavy silver and light silver springs. 900 ish rpm at idle in park and 800 in drive. I also put the lightest metering springs in the carb.
I haven't looked at the AVS2. Are the metering springs controlling rods that gointo the main jets? if so, that shouldn't effect idle.
The car runs well but when the fans come on at idle in gear it just sounds like it’s off a bit. The Rpms fluctuate and just doesn’t sound right to me. It doesn’t flood or die just again doesn’t sound/feel right. I’ve tried to add some advance and that helps, but then my total timing gets way up there and that kinda scares me.
Between that, and the drop of rpm from 900 to 800, it seems like the load with fans on is just borderline too much.
Have you experimented with richer idle mixtures?
I would first turn the idle mix screws in (leaner) to get a sense of how much control they are providing. Then assuming they have some effect, make them richer. If you can make them rich enough the rpms and/or vacuum at idle drops, then we know they have sufficient control over the idle mix. Set them an 1/8 or a 1/4 turn richer than the current setting and see if the engine can handle the loads at idle a little better.

Do all that at 18* initial.

Then you could test again at 20*, reset the throttle position for 900 rpm in neutral and do the whole test procedure over.
See if its better in gear with the fans on at idle.

If 20* works out better, then you can buy different bushings from crackedback or modify as shown here
MSD-Delco Distributor Weight Modification For Less Advance
(don't join tapatalk if they ask, unless you really want to)

I'm assuming here that the fans are drawing enough current that additional load is from the alternator spinning with a strong magnetic field.

If there is no vac advance on this distributor, then use a pair of equal medium or light springs.
 
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I have a similar issue with my Contour fans and big-cam 451. They draw quite a bit of current - haven't directly measured it yet, but I think it's in the neighborhood of 40 amps. Allowing for alternator inefficiency, that's close to 3/4 of a hp. Definitely noticeable at idle when you don't have much torque there!
 
I haven't looked at the AVS2. Are the metering springs controlling rods that gointo the main jets? if so, that shouldn't effect idle.
The AVS2 is pretty much the same as an avs but has annular discharge primary venturies.

Will be looking into the bushings.

as for the rest I am able to lean or richer with the screws and I have tried fattening it up a bit at a few different initial timing settings. It doesn’t help much till you get to 24-30*
 
I have a similar issue with my Contour fans and big-cam 451. They draw quite a bit of current - haven't directly measured it yet, but I think it's in the neighborhood of 40 amps. Allowing for alternator inefficiency, that's close to 3/4 of a hp. Definitely noticeable at idle when you don't have much torque there!
I also have the Contour fans and yeah it’s a heck of a draw. I do have a decent alt and definitely can feel the load.
 
Oh and I changed the springs because I have 9” of vacuum in drive at the 18* so I was just guaranteeing the rods stayed down at idle.
 
The AVS2 is pretty much the same as an avs but has annular discharge primary venturies.

Will be looking into the bushings.

as for the rest I am able to lean or richer with the screws and I have tried fattening it up a bit at a few different initial timing settings. It doesn’t help much till you get to 24-30*
Was it idleing as well or stronger with the FI? If so did you have a map of rpm, MAP/Vac, and timing?

The typical Carter idle system is a bit different than the Holley. The fuel to the idle port is shared sequentially after the trasnfer slot. The Carters usually have two restrictions and a second air jet. I haven't messed with them. Its its a neat system but I can't offer any suggestions on a smart way to test or change for your engine's needs.

If 24* seems to be the minimum it likes, maybe that the baseline and experiment with fueling timing from there.
 
With the FI it would idle well. Had the timing at 18 initial and 36 all in at 3k. It was around 10” in drive at idle. It would bounce the timing around at idle to compensate for cam and other conditions. Definitely a benefit with the FI.
 
With the FI it would idle well. Had the timing at 18 initial and 36 all in at 3k. It was around 10” in drive at idle. It would bounce the timing around at idle to compensate for cam and other conditions. Definitely a benefit with the FI.
OK. Then it does seem like the benefit of additional timing at idle is the effect on the idle circuit. I don't see why else it would run strong with 18* in gear with FI and not so with the carb. Need to find some Carter/Rochester guys that have run them on radical engines. Its done. Just less common.
This is about all I know is the theory.
Operational theory of the Carter idle restricions & air bleeds

Change any links to imperialclub from .org to .com
 
OK. Then it does seem like the benefit of additional timing at idle is the effect on the idle circuit. I don't see why else it would run strong with 18* in gear with FI and not so with the carb. Need to find some Carter/Rochester guys that have run them on radical engines. Its done. Just less common.
This is about all I know is the theory.
Operational theory of the Carter idle restricions & air bleeds

Change any links to imperialclub from .org to .com
Also with the FI it controlled the fans and it would bump up the idle when the fans came on. FWIW the motor doesn’t seem to care where the timing is except for at idle, it runs like a scalded ape when you push on the pedal! LOL
 
Also with the FI it controlled the fans and it would bump up the idle when the fans came on
Then I'm wrong, at least to some extent. If it bumped timing and maybe rpm ? then my assumption that is strong idle doesn't hold up.

Worst case you could install a the idle solenoid like those used on some A/C equiped cars to bump the idle speed up under load.
 
I'd check voltage at your coil with the fans on.

You don't mention if you've made any wiring changes to the charging system. It's possible to have it wired in a way that winds up dropping volts to your coil when the fan comes on.
 
I'd check voltage at your coil with the fans on.

You don't mention if you've made any wiring changes to the charging system. It's possible to have it wired in a way that winds up dropping volts to your coil when the fan comes on.
I will check into that. The coil is powered by the MSD box and the box is wired directly to the battery. I suppose there could be a voltage drop to some degree. Although according to my gauges I haven’t seen anything under 13v. But I will definitely check.
 
I wonder if the MSD is picking up some type of interference from the fans? But I would expect that if there was interference it would happen at any speed when the fans are on.
 
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I will check into that. The coil is powered by the MSD box and the box is wired directly to the battery. I suppose there could be a voltage drop to some degree. Although according to my gauges I haven’t seen anything under 13v. But I will definitely check.

I've seen some strange stuff in the past. A drop from the dash to the battery could be enough.. It's hard to say without knowing how your alternator wiring and voltage gauge is setup, but it's always a good thing to check. Low volts causes so many headaches that can be tough to trace..

Interference can be possible too. It would definitely be there at all revs, but minor changes are most notable at idle, so you just may not feel it elsewhere.

Both are longshots versus simple increased load from the alt, but worth investigating if you can.
 
Well an update, 13+ volts at idle in drive with fans on. Set the timing back to 18* with lighter springs so the advance comes all in at 2500 -2800rpm. Took her for a decent cruise including a short stint on the freeway. Ran real well but again at extended idle in drive at stoplights the idle was odd. Noticed however that it did it even with the fans off. It would happen faster with the fans on but still would happen with them off. Curious...
 
Ok, I believe I have this one licked! As I sat and listened to the car in drive at idle with fans on it just seemed as it was intermittently dropping a hole. Had the wife hold the brake as I just watched and listened.... low and behold I heard a tick then saw an arc! Bingo! Thinking I may need to fatten it up at cruise a smidge, that may drop the cylinder temps a little? Thoughts?

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That stuff would probably work if you had problems with burning the wires... but a lot of headers burn the boot directly. Besides, it's still $60.

On my Hedman 78030 (B-body) headers a straight boot is required on plug #5, so I had to buy an extra single wire. No way an angle boot would work there. The Accel straight one is a long ceramic piece that keeps the wire well away from #5 tube.
 
That stuff would probably work if you had problems with burning the wires... but a lot of headers burn the boot directly. Besides, it's still $60.

On my Hedman 78030 (B-body) headers a straight boot is required on plug #5, so I had to buy an extra single wire. No way an angle boot would work there. The Accel straight one is a long ceramic piece that keeps the wire well away from #5 tube.

Not trying to horn in here , but I caught 2 boots burning before any shorting out and wrapped them w/ some left over header wrap , has worked so far ----------
 
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