NEED VACUUUUUUUM LINE HELP

[BigPapaRoss]

*need help with vacuum lines*

I have a Festy 88', stock carb had to gooooo. I had a punch in piston 3 and backfill to the carb.... you know how that goes. I got a new CARB (p0hoto 4) and it has only 4-5 vacuum plugs, I just don't know how to hook it up, what I should do and what to do with all theese lines still in the car. Any help is good help. ty.

[WmWatt]

I notice in the first two photos that the EGR valve by the pasenger side strut tower is missing as are the three plastic solenoids on a missing bracket on the firewall in the centre. I do see the black charcoal cannister by the driver's side strut tower which stores gasloline fumes for burnning when the engine is started and doesn't let them leak out into the atmosphere. There are also two vacuum lines which feed the standard distributor. One of those is a vacuum advance which works in conjunction with the mechanical advance. The old carb will have a silver coloured cutoff valve on it's the top front with four vacuum hoses which might not appear on your replacement carb. If you search this webiste on vacuum hoses (lines?) you'll find more information as the topic has come up before. Have fun. That's a nice clean looking engine compartment.

PS Do you think that carb will work? It says 1983 1.6L when the Festiva is 1988 1.3L. The original carb is Japanese made for Mazda 1.3L B3 engine. I think people usually substiturte a Weber or Ford Escort carb and disconnect most of the emissions devices. Sorry I can' be of more help.

[BigPapaRoss]

I did some R&D on how carbs works and asked around before I went slapping this one on there. I will post my results in this thread. thanks you for the help

[zoe60]

It looks just like my Escort carb. If you look at the fuel cut solenoid, there is a vacuum port just to the right side of it. Plug a vacuum line in there, and run it to the vacuum advance on the distributor. Split it and feed it to both ports. Block off the other ports. Any where else you need vacuum needs to be hooked to the intake manifold. If you get it running right, you will love your new carb. Good choice!

[ricko1966]

I'm running the same carb.hooked everything to manifold vacuum, no egr. Hooked advance side of distributor can to manifold vacuum left the other distributor port open. People will argue that manifold vacuum to distributor vacuum advance is wrong, but it's not. Ported vacuum came about as an emissions control, the timing retards at idle letting the air fuel burn later cleaning up exhaust emissions at Idle.Ported vacuum and manifold vacuum match except for at idle.Distributor hooked to manifold vacuum gives maximum advance at minimum throttle opening for mpg. At increased throttle opening manifold vacuum decreases so advance decreases so less chance of detonation.Applying equal vacuum to both sides of the advance cannister makes absolutely no sense to me because they advance and retard would have equal pressure so they would cancel each other. If I'm wrong someone please explain it.

[zoe60]

Well, I tested the two ports on the distributor a long time ago. I just sucked on a piece of vacuum hose hooked up to each port while looking at the crank with a timing light. What I found is that both ports advance vacuum. If I wyed them the vacuum advanced even more. I hooked my Escort carb's vacuum port next to the idle mixture adjuster screw to a tee and to both distributor ports. I set the timing to about 8 degrees advanced at idle. I may have it all wrong, but my car runs great. No complaints whatsoever. Peppy. Been like that for about five years now and I wouldn't be afraid to drive it a thousand miles. Easy to test for yourself if you have a timing light and a hose to fit.

[theastronaut]

I'm running the same carb.hooked everything to manifold vacuum, no egr. Hooked advance side of distributor can to manifold vacuum left the other distributor port open. People will argue that manifold vacuum to distributor vacuum advance is wrong, but it's not. Ported vacuum came about as an emissions control, the timing retards at idle letting the air fuel burn later cleaning up exhaust emissions at Idle.Ported vacuum and manifold vacuum match except for at idle.Distributor hooked to manifold vacuum gives maximum advance at minimum throttle opening for mpg. At increased throttle opening manifold vacuum decreases so advance decreases so less chance of detonation.Applying equal vacuum to both sides of the advance cannister makes absolutely no sense to me because they advance and retard would have equal pressure so they would cancel each other. If I'm wrong someone please explain it.

The main chamber goes to ported vacuum which is only active at part throttle- less than 1/4 throttle. This gives you extra advance on top of the centrifugal advance at low load/part throttle cruising for extra mileage when detonation is unlikely with lower cylinder temps. The leaner mixture you should be tuned for on the primary barrel idle jet for part throttle/low load conditions needs extra timing since lean mixtures burn slower. This is how you get the most mileage and throttle response.

The smaller top chamber is hooked to manifold vacuum and pulls back against the ported vacuum chamber to limit vacuum advance under certain conditions. Neither have much vacuum at WOT so advance decreases for less chance of detonation and since richer mixtures need less timing to burn completely.

So, both ported and manifold chambers are needed.

[ricko1966]

Damnit guys I'm so sorry. Was posting from memory something I did 8 years ago. I'm not running a festiva vacuum advance. I'm running a single chamber off a mazda on manifold vacuum.

[ricko1966]

Damnit guys I'm so sorry. Was posting from memory something I did 8 years ago. I'm not running a festiva vacuum advance. I'm running a single chamber off a mazda on manifold vacuum. So I'm running 36 degrees total and pulling in another 12 degrees at light load cruise.

[ricko1966]

Please read this. I've been using this as my guideline for years. Give me your take on this please. Seems like I might need to break out a vacuum pump and some gauges and do some investigating. Not trying to start a war, trying to figure out if I've been misinformed.Thanks

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 "whiz-bang" 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, drivability, 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.

Courtesy John Hinckley
Retired GM/Chrysler Engineer

[theastronaut]

It's not wrong, there is more than one way to make vacuum advance work. The stock carb'd Festiva distributor uses two chambers- ported and manifold to vary timing using both signals, although the main chamber is ported. It is important to have vacuum advance along with centrifugal as that article states. Idle mixture shouldn't be all that lean, and WOT shouldn't be rich enough that the burn rate becomes lazy (requiring even more advance). B3's have such a small and efficient chamber that they don't need a lot of advance anyway, so as long as the A/F mixtures are reasonable I don't think we'll gain anything over getting away from the stock vacuum advance setup.

Throwing an Escort or Weber carb on requires tuning the jets and idle mixture, it'll run excessively rich with an Escort carb.

70's aircooled VW's ran ported vacuum on models with centrifugal/vacuum advance Bosch 034 distributors, and those ran great and got great mileage. The initial timing was set to around 7-10 degrees, total timing was 28-30ish, and off idle the ported signal at low speeds/low load kicked in around 10 extra degrees of advance for more mileage when on the leaner idle jet circuit. The added vacuum advance would drop out with more throttle for the richer mixed on the main jet circuit.

American V8's go about it backwards from that- adding advance with high manifild vacuum at idle, then dropping vacuum advance as manifold vacuum drops with more load/increased throttle. If you lose vacuum advance for any reason your car won't idle and will be sluggish at low loads. With the VW ported setup idle won't change if you lose vacuum advance, and WOT power will stay the same, which is where you spend most of your time in a 50 hp car anyway lol.

[ricko1966]

Thanks for the explanation. Now the VW carb wasn't using ported vacuum it was pulling vacuum from the venturi and using manifold vacuum. Most carbs that I've dealt with are using ported vacuum and manifold vacuum with the only difference being that manifold vacuum is below the throttle plate and ported vacuum is above the throttle plate and they match after the throttle is open.So in my mind I'm still thinking that unless you have venturi vacuum available, a single advance chamber on manifold vacuum would be the way to go. My thinking being the only time you would get any advance if you have equal vacuum on each side of the chamber would be when the throttle plates were closed and so no there is no vacuum on the ported port and full vacuum on the manifold port.