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Author Topic: Flat spot with Holley 350 carb  (Read 36457 times)

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Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #30 on: April 25, 2014, 02:45:48 PM »
i thought that was the case but when driving the car around with a vacuum gauge hooked up it still pulls vacuum at a cruise.  drops down to 6-7" until you go past half throttle or so.  im only mentioning this because it may be seeing a lot of advance at a cruise, and this is the same at light cruise whether ported or manifold.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #31 on: April 25, 2014, 05:52:53 PM »
You want vacuum at cruise for more advance that's where the mileage comes in, you can get adjustable vacuum canisters to adjust the amount of advance if it starts to ping at cruise.... Here is an article about vacuum advance that will help understand the purpose/function of vacuum advance..

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
______________ ____
Art
65 Falcon 2DR 200 IL6 with C4.

Offline Clydesdale80

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Re: Flat spot with Holley 350 carb
« Reply #32 on: April 26, 2014, 03:39:05 PM »
I just read this on another forum the other day lol.  There seems to be widespread confusion about this topic.
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Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #33 on: April 26, 2014, 05:53:29 PM »
That article is on just about every automotive related site out there, I snagged it from a Ford site this time, LOL. Don't know what the confusion is though..
Art
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Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #34 on: April 26, 2014, 07:36:51 PM »
Found what I was looking for-the 350 Holley may well be a moot point.

June 1983 Popular Hot Rodding, '2.3 Liter Ford Power Tricks' article by Dave Vizard........ .

The stock 2.3 intake is a bottleneck past about 250-275 cfm carb. He flow tests the stock intake with stock 5200 and then same intake with 350 Holley, both flowed while bolted to a head. The 5200 carb flowed 117 cfm including air filter, the 350 flowed 119.

That's TWO measly cfm for the bigger carb, it doesn't help there at all, the manifold kills it.

The article also shows the Offy plus 390 Holley 4 bbl. does not flow as well as the 2.0 intake with adapter on the 2.3 plus a Holley 2 bbl. Even with the 2.0/2.3 mismatch that occurs there because of different runners.

Offline dick1172762

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Re: Flat spot with Holley 350 carb
« Reply #35 on: April 26, 2014, 11:01:43 PM »
Racer Walsh once told me that the 2.0 intake with a 500 Holley 2 barrel, made with in 5 HP of the best he ever got with weber side drafts. And this was on a dyno. Best stock intake ever???? Sure sounds like it.
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Offline jeremysdad

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Re: Flat spot with Holley 350 carb
« Reply #36 on: April 26, 2014, 11:07:03 PM »
Racer Walsh once told me that the 2.0 intake with a 500 Holley 2 barrel, made with in 5 HP of the best he ever got with weber side drafts. And this was on a dyno. Best stock intake ever???? Sure sounds like it.

IT IS a pretty good stock intake...but the short 2&3 runners...it should be even...the runners need to be even! :)

Offline Srt

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Re: Flat spot with Holley 350 carb
« Reply #37 on: April 27, 2014, 03:37:03 AM »
IT IS a pretty good stock intake...but the short 2&3 runners...it should be even...the runners need to be even! :)


i had a manifold that came over from europe (don't know if it was from the UK or Germany) on my 2.0 that had the #'s 1 & 4 runners meet the plenum at the inside (cylinder head side) and the #'s 2 & 3 runners meet the plenum at the outside (fender well side).


made for a more favorable combination of runner lengths.


it was a Ford OE part but from what i haven't a clue.  in my case it did help with fuel distribution issues concerning #'s 1 & 4 running lean at high boost levels.


the occurrence of melted pistons in those holes was darn near eliminated.  prior to the use off this manifold those two rascals were draining my wallet pretty fast!


 
the only substitute for cubic inches is BOOST!!!

Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #38 on: April 27, 2014, 04:48:21 AM »
While one of the first things you look for is for the runners to be even, it is more about area. Shorter runners can be slightly bigger in size and have the same area as longer ones with smaller diameters. How Edelbrock made millions with the Torker intakes, the runners were all different sizes. They assured you in every set of instructions that if you matched ports to head you just destroyed the manifold. The engine sees the area more than the length since they are all too short anyway, tuned length has them more like EFI manifolds now, or much longer.

I do not know if the 2.0 intake has different areas in runners or not but Vizard swore by the fact the manifold was also very efficient runner to runner. Like 93% or so. So sometimes appearance can be deceiving. Part of it to me is the much better plenum shape, which just blows a 2.3 plenum all to h-ll. The 2.3 has jagged points sticking out and dead flat with no room to turn at all. EGR plate just makes it worse. Worst of the worst there. The 2 & 3 are even worse, half the port is missing inside the plenum so maybe 2 inches long. All hard angles and calculated to not flow smooth. Airflow loves gradual turns, i.e. the 2.0.

Motors can be funny things, sometimes what looks right is not, that article pointed that out about the stock 2.3 intake as far as just viewing it from the outside. It's a real disaster once you look under the carb and there's no fixing it.


Offline dick1172762

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Re: Flat spot with Holley 350 carb
« Reply #39 on: April 27, 2014, 08:57:46 AM »
I did ever thing I could think of to 2.3 intakes and it only made them worse. I welded them, ported them, added dividers, cut-welded-beat-ground and in ever case, it ran the same. Then I talked to a Ford tech who told me that on the dyno it made no difference what carb was used, the 2.3 put out the same HP. Why? Cause that's all the intake would flow. JUNK!!!!
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Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #40 on: April 27, 2014, 10:03:42 AM »
Guess that settles that, LOL..
Art
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Offline Clydesdale80

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Re: Flat spot with Holley 350 carb
« Reply #41 on: April 27, 2014, 01:58:47 PM »
Found what I was looking for-the 350 Holley may well be a moot point.

June 1983 Popular Hot Rodding, '2.3 Liter Ford Power Tricks' article by Dave Vizard........ .

The stock 2.3 intake is a bottleneck past about 250-275 cfm carb. He flow tests the stock intake with stock 5200 and then same intake with 350 Holley, both flowed while bolted to a head. The 5200 carb flowed 117 cfm including air filter, the 350 flowed 119.

That's TWO measly cfm for the bigger carb, it doesn't help there at all, the manifold kills it.

The article also shows the Offy plus 390 Holley 4 bbl. does not flow as well as the 2.0 intake with adapter on the 2.3 plus a Holley 2 bbl. Even with the 2.0/2.3 mismatch that occurs there because of different runners.

Does anyone know where to find this article online? If not, would it be possible for you to scan and upload it?  I'm sure many people on this site would find it interesting.  I searched for it but google didn't turn up anything this old.
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Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #42 on: April 28, 2014, 02:01:38 AM »
How do they feel here about copyrighted material from a company that is still in business? Some places get pretty uptight about it, you can be sued over it. I see this in the onsite registration agreement..... ......they refuse responsibility in the standard disclaimer and put it all on me, don't really wanna go there.

'You also agree not to post any copyrighted material unless you own the copyright or you have written consent from the owner of the copyrighted material.'

I do see some stuff in the onsite articles from Car Craft and Hot Rod. Is Car Craft magazine still around?

Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #43 on: April 28, 2014, 07:00:29 AM »
74 pinto wagon, i have read that article before, straightened me out on where to run the vacuum.  my only reason for thinking ported may work here is because of the very high advance saw at idle. it's most likely fine under load.  i didnt know if there was adjustable vacuum canisters for the ford distributors. ive used the crane adjustable canisters on the gm distributors and they work well.  i still feel as though i may need a bigger range of centrifugal advance.  i only get 21 degrees out of it.  to get 36 total that gives me an initial timing of 15 degrees.  Should i grind the weight or look for a different set?

After reading about some other distributors on the early models, a 1980 2.3 wouldn't have a timing retard port on it would it?  i only see one vacuum port and it definitely advances the distributor.

As far as the intake and carb, i only switched to the holley 350 for ease of use.  Wasn't so much concerned with increasing hp.  The stock weber is an octopus of vacuum lines and it kept sticking throttle position at half to 3/4.  Must have been some fast idle setting issue or something wearing out, but wouldnt go away even when warm.  these little cars can be hard to stop at a stop sign on wet pavement when the throttle doesnt return.  that is one thing i cant stand so we just switched to the holley since i already now them inside and out and all tuning parts are readily available.

A 2.0 intake is the way to go?  What about late model intakes off mustangs and rangers?  Isn't the EFI intake a good swap?  I think those use a 4 barrel throttle body but an adapter could be used for the 2 barrel right?

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #44 on: April 28, 2014, 08:10:47 AM »
You always have vacuum at at idle that's ok, it idles a lot smoother and the throttle can be closed a lot further exposing less transfer slot. You can get aftermarket canisters that have an adjusting screw and some have a shorter slot to limit the travel, but if it don't rattle at cruise you're ok. I'm new to these little motors so I'm learning this stuff, but just looking at these intakes the lower EFI gotta be way better, already have the intake and header for mine just need the carb, the Autolite I want seems petty hard to find but as soon as I find one I'll be doing the switch, adapter don't look hard to make, already found a chunk in the scrap, er, I mean material bin to make one.
Art
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Offline Clydesdale80

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Re: Flat spot with Holley 350 carb
« Reply #45 on: April 28, 2014, 10:16:28 AM »
How do they feel here about copyrighted material from a company that is still in business? Some places get pretty uptight about it, you can be sued over it. I see this in the onsite registration agreement..... ......they refuse responsibility in the standard disclaimer and put it all on me, don't really wanna go there.

'You also agree not to post any copyrighted material unless you own the copyright or you have written consent from the owner of the copyrighted material.'

I do see some stuff in the onsite articles from Car Craft and Hot Rod. Is Car Craft magazine still around?

ok, I hadn't thought about that.  I sure don't want to get anyone in trouble.
Bought a 1978 hatchback to be my first car.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #46 on: April 28, 2014, 10:28:41 AM »
How do they feel here about copyrighted material from a company that is still in business? Some places get pretty uptight about it, you can be sued over it. I see this in the onsite registration agreement..... ......they refuse responsibility in the standard disclaimer and put it all on me, don't really wanna go there.

'You also agree not to post any copyrighted material unless you own the copyright or you have written consent from the owner of the copyrighted material.'

I do see some stuff in the onsite articles from Car Craft and Hot Rod. Is Car Craft magazine still around?
Yep they're still around, if articles are on the net and you can copy/paste than it's not copyrighted anymore, you see articles pasted on every board around, every time I run across something copyrighted it won't let me copy it, so far I haven't been able to anyhow...

http://www.carcraft.com
Art
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Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #47 on: April 28, 2014, 02:26:10 PM »
74 pintowagon which intake are you going to use?

i do have what i think is a slight ping rattle at light cruise, especially up a small grade so i think i may need to either limit vacuum advance or increase my centrifugal range higher than 21 degrees.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #48 on: April 28, 2014, 02:56:16 PM »
I got the lower EFI intake seems like the one to use. Changing the centrifugal will not change the vacuum advance, you need to limit the travel of the vacuum unit that's why you get adjustable ones, or one that has less travel, if it's pinging very little you could back it off a degree and try it don't take much sometimes.
Art
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Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #49 on: April 28, 2014, 03:11:48 PM »
it is pinging very little.  just frustrated that my total is only at 32 and initial is at 11.  i figured if a lower static centrifugal number could be achieved, when combined with vacuum it might not ping then but still advance to 34-36 range which ive been told is optimum with these motors.  i can bump the timing back to 8 or so initial and probably be all set but then my total is back to 29 or so.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #50 on: April 28, 2014, 05:37:37 PM »
You should be at 36 get yourself an adjustable canister or one with a shorter slot. BTW, what rpm does your total come in?? it should be all in by 2700-2800...
Art
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Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #51 on: April 28, 2014, 08:42:32 PM »
Alter the vacuum slot yourself.

Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #52 on: April 28, 2014, 09:48:17 PM »
i'll try and find a tach and see when im getting total in.  if i need to change can you use the different color springs like crane sells for the chevys?  not sure if the ford is a different size,  already have some if the chevy springs fit.

im all for altering what i have.  im sure i can limit the vacuum easy enough.  if i set this thing at 36 total, what is an acceptable range for initial?  i was told 10 earlier in this thread.  i just can't do that without modification. that's 26 degrees centrifugal advance. i'll alter the weights/stop if i have to, just curious if its even necessary if some of you are running a very high initial without issue.

Offline dick1172762

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Re: Flat spot with Holley 350 carb
« Reply #53 on: April 28, 2014, 10:59:48 PM »
AT this point, you would be better off going back to the stock 36/32 carb unless you just want all these problems.
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Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #54 on: April 29, 2014, 07:33:17 AM »
i'll try and find a tach and see when im getting total in.  if i need to change can you use the different color springs like crane sells for the chevys?  not sure if the ford is a different size,  already have some if the chevy springs fit.

im all for altering what i have.  im sure i can limit the vacuum easy enough.  if i set this thing at 36 total, what is an acceptable range for initial?  i was told 10 earlier in this thread.  i just can't do that without modification. that's 26 degrees centrifugal advance. i'll alter the weights/stop if i have to, just curious if its even necessary if some of you are running a very high initial without issue.
Check the advance slot if you're on the narrow one rotate it to the wide one, if you're on the wide one grind a little don't take much though to make a difference. Don't remember about the springs just take one off and compare them. I just bought a reman Duraspark for mine and it's out to lunch, my initial is 18 and all I get is 32, gotta dig into that soon..
Art
65 Falcon 2DR 200 IL6 with C4.

Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #55 on: April 29, 2014, 06:33:39 PM »
IIRC used to be Ford and GM used different advance springs. Mr. Gasket made a set of earlier curve ones for each. We used the GM ones on AMCs since the distributor was a GM Delco-Remy one.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #56 on: April 29, 2014, 09:50:25 PM »
Art
65 Falcon 2DR 200 IL6 with C4.

Offline kerryann

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Re: Flat spot with Holley 350 carb
« Reply #57 on: April 30, 2014, 09:46:40 AM »
hey thanks for those links, thats exactly what i needed.  going to fine tune the centrifugal advance next chance i get.  should solve my timing problem.  the car must be set on 10L right now, or have a problem there thats not allowing it to fully advance.  i'll worry about the speed that it all comes in at after.  the pinging should go away if i can limit the initial.

im never going back to that 36/32 carb. still have it sitting in the basement if someone is interested in one.  car was undriveable with it.  i know they can be fixed.  just don't want to learn those carbs, don't care for the dozens of vacuum lines everywhere either.  holleys are all pretty much the same and the easiest to work with.  flat spot is just about gone.  i'll get back on that issue as soon as im happy with my timing curve.  might be on the hunt for a better intake soon as well.  thanks for all the help so far.

Offline 74 PintoWagon

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Re: Flat spot with Holley 350 carb
« Reply #58 on: April 30, 2014, 09:59:04 AM »
The initial won't help the pinging, if it only pings at cruise you need to limit the vacuum advance. First thing you need to do is set the centrifugal vacuum is last, get the right curve and set the total where you want it, drive it without vacuum hooked up, it shouldn't rattle through the rpm range if it does you'll have to back it down some, after it's right then set your vacuum advance.
Art
65 Falcon 2DR 200 IL6 with C4.

Offline amc49

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Re: Flat spot with Holley 350 carb
« Reply #59 on: April 30, 2014, 10:10:34 AM »
X2..........

'holleys are all pretty much the same and the easiest to work with.......... ..'

I for one do not agree, if you truly understand how a Holley works then you already understand how others work as well, it becomes simply a take-it-apart-and-see-how-they-do-it exercise after that. The 32/36 is mucho more adjustable than the Holley and dead reliable. It will get better mileage too. The flat spot here may well be Holley induced, or the difference between calling one booster online vs two, four cylinders will initiate flow faster at a single venturi than two of them.

Start simply switching metering blocks out on Holleys and quickly find out about how they are 'all pretty much the same'.............. ..taint so. I've certainly straightened out enough of them that were butchered by so-called 'experts'. Correct metering block on carb is check #1, you'd be amazed how many mess up a block and swap wrong one to have the carb go to crap, then they cannot figure out what's wrong. Or piece one carb together from five then want $150 for junk. If numbers don't match I don't touch them, a waste of time. Having a Holley on it is much more likely to run into trouble later, they always want to screw with it. The other brands highly likely to have a virgin carb, they are scared of them. You have no idea how many Holley sales I stifled back in the day by simply changing or fixing a $20 issue on a carb the person was afraid of. They always wanted to 'put a Holley on it' (sound familiar?), much of the time they realized later it was a mistake. Holleys never get as good mileage as OEM carbs, they are metered rich for performance and utterly destroy emissions levels. When they insisted I always added 'keep the old carb!', often it went back on the car.

Holleys are great for power but almost nothing can repeat the driveability of an OEM carb in proper working order on almost every vehicle out there. They don't spend millions in carb/engine research for nothing there.